- Email: [email protected]
Diagnostic significance of autoantibodies in autoimmune chronic active hepatitis
CLINICAL
Diagnostic Significance of Autoantibodies in A u t o l m m u n e Chronic Active Hepatitis Robert M. Nakamura Department of Pathology, Scripps Clinic and Research Foundation, California at San Diego School of Medicine, La Jolla, California
David J. Bylund Section of Transplantation Immunology, Department of Pathology, Scripps Clinic and Research Foundation, La Jolla, California
here is significant evidence for the existence of autoimmune liver disorders.lS'3S'4° These diseases are characterized by organ-specific and many non-organ-specific autoantibody markers. The autoimmune liver diseases may be broadly placed into three groups:
T
1. Primary biliary cirrhosis (PBC). 2. Autoimmune chronic active hepatitis (ACAH). 3. "Certain cases of cryptogenic cirrhosis. The autoimmune liver diseases are often associated with certain histocompati-
bility antigens [human leucocyte antigen (HLA)], such as HLA-A1, HLA-B8, and HLA-DR3, which suggest a genetic predisposition. 3° In many of the autoimmune liver disorders, the exact etiology and nature of primary insult on the parenchymal hepatic cells is unknown. The mechanism of injury may be due to cytotoxic lymphocytes which attack antigens exposed on the hepatocyte membrane. Lymphocytes recognize a, membrane antigen only if it is associated with the HLA determinants on the host membrane. 18,38,4o This report will discuss the various associated organ-specific and non-organ-
specific antibodies associated with autoimmune chronic active hepatitis. The emphasis will be placed on the diagnostic value of the various autoantibodies as well as their usefulness in prognosis.
Autoantibodies: General Overview Characteristic autoantibodies are seen in autoimmune liver diseases. The specific role of the autoantibodies in the pathogenesis and course of the diseases remains unknown, but they are of diagnostic significance. 1 In ACAH, anti-smooth muscle antibodies (SMA) and antinuclear antibodies continued on page 162
Striational Autoantibodies: Paraneoplastic Antibodies Associated w i t h Thymoma and Myasthenia Gravis Carol L. Williams and Vanda A. Lennon Neuroimmunology Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota
S
triational autoantibodies (StrAb), which bind to the contractile elements of striated muscle, were first discovered in the serum of patients with myasthenia gravis (MG) over 3 decades ago. 22 This provided the first serological evidence that MG is an autoimmune disease, and generated speculation that CIMNDC I1(I I)161-176,1991
Elsevier
antibodies might cause the muscle weakness that is characteristic of MG. Further interest in StrAb was stimulated by the observation that these antibodies also bind to epithelial and myoid cells in the thymus, s'16'23'26'27'30 indicating common antigens in muscle and thymus. After the continued on page 167 0197-1859/91/$0.00 + 2.20
162 C L I N I C A L I M M U N O L O G Y
TABLE 1.
Newsletter
Vol
AUTOANTIBODIES IN ACAH ~ (I) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
Antismooth muscle antibodies Anticytoskeletal antibodies Anti-liver-kidney microsomal antibodies Anti-liver cytosol antibodies (LC-I) Anti-soluble liver antigen antibodies Antimitochondrial antibodies Anti-liver membrane antibodies Antinuclear antibodies Antibodies to nuclear lamin Liver-specific antibody Asialoglycoprotein receptor antibody Other
From references 18, 38, and 40. (ANA) are commonly found. The l i v e r kidney microsomal (LKM) antibody characterizes a type-II subgroup o f A C A H 38 diagnosed mainly in children who are often negative for all other autoantibodies. Another subgroup of A C A H is characterized by antibodies against a soluble liver antigen (SLA). 32 There are many mitochondrial antibodies associated with various liver and other diseases. 4 Primary biliary cirrhosis (PBC) is almost always associated with specific antimitochondrial antibodies. Mitochondrial antibodies are occasionally observed in A C A H . However, A C A H is characteristically associated with a variety of autoantibodies, listed in Table 1, The autoantibodies associated with the subgroups of A C A H are shown in Table 2. The S M A , A N A , L K M , and A M A antibodies can be diagnosed by an indirect immunofluorescent method. HowTABLE 2.
ever, anti-SLA is detected by an immunoblotting or radioimmunoassay method. ~,38
General Diagnostic Value of Autoantibodies The predictive value of the various tests for autoantibodies is dependent upon the prevalence of the disease, t 1 The predictive value of a test with a sensitivity of 100% and a specificity of 99% is only 0.1% if the disease has a prevalence of 1 in 100,000.1 In one European study, the incidence o f classical A C A H and A C A H type 2 with L K M antibodies was 2.2 and 0.5 per 100,000, respectively. 13
Chronic Active Hepatitis ( C M t ) and Autoimmune Chronic Active Hepatitis Autoimmune hepatitis was described during the 1950s as an entity called chronic active hepatitis. 28 Chronic active hepati-
1 1, No. 1 1, 199 1
tis is diagnosed by clinical and histological findings. The characteristic "~hallmark" lesion of CAH is piecemeal necrosis (PN), which is characterized by a prominent lymphohistiocytic infiltrate causing liver cell necrosis at periportal and/or paraseptal mesenchymal/parenchymal junctions. -~'5° PN, although characteristic of A C A H , is not pathognomic, being seen also in viral and drug-associated chronic hepatitis, primary biliary cirrhosis, alcohol-induced liver disease, W i l s o n ' s disease, and alpha-l-anti-trypsin deficiency. 29'41"5° PN may progress to bridging necrosis with fibrosis and eventually irreversible cirrhosis. Lymphocytic piecemeal necrosis is best explained as an immune attack against the periportal and paraseptal hepatocytes. The most likely target antigen would be in the surface membranes of hepatocytes. Direct immunofluorescence studies have shown that IgG is detected in a linear pattern on the hepatocyte surface membrane, z9 Classification of C A H Mackay has classified C A H into several groups of different or unknown etiologies. 18,29,38,40 1. CAH-A: autoimmune. 2. CAH-B: hepatitis B virus (HBV) and hepatitis D (HDV) virus. 3. CAH-C: cryptogenic (autoantibody negative), hepatitis B surface antigen (HBsAg) negative. 4. CAH-D: drug induced, that is, oxyphenisatin and methyldopa.
AUTOIMMUNE CHRONIC ACTIVE HEPATITIS SUBGROUPS a
Antibody
Classic "Lupoid"
SMA Antibody Positive
LKM Antibody Positive
SLA Antibody Positive
ANA SMA SLA AMA LKM LMA
+ + +
+ +/-
+ -
+ /+ +/+ /-
a Fromreferences18.38, and 40.
5. CAH-E: ethanol induced. 6. CAH-N: unknown virus other than hepatitis A, B, or C. CAH-B cases usually have H B s A G in the blood. Hepatitis D virus (delta agent) is associated with hepatitis B as a coinfection. Many of the cases of the cryptogenic group can now be attributed to infection with hepatitis C virus (HCV).
CLINICAL IMMUNOLOGY NEWSLE'ITER (ISSN 0197-1859) is issued monthly in one indexed volume per year by Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010. Subscription price per year: $125.00. For surface airlift add $37.00. Second-class postage paid at New York, NY, and at additional mailing offices. P U l m u t ~ : Send address changes to Clinical Immunology Newsletter, Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010. NOTE: No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use of operation of any methods, products, inst~ctions for ideas contained in the material herein. No suggested test or procedure should be carried out unless, in the reader's judgment, its risk is justified. Because of rapid advances in the medical sciences, we recommend that the independent verification of diagnoses and drug dosages should be made. Discussions, views and recommendations as to medical procedures, choice of drugs and drug dosages are the responsibility of the authors.
0197-1859/91/$0.00 + 2.20
© 1991 Elsevier Science Publishing Co., Inc.
C L I N I C A L I M M U N O L O G Y Newsletter 163
Vol. 11, No. 11, 1991
Classic ACAH or "Lupoid Autoimmune Hepatitis" The CAH-A group, or classic autoimmune chronic active hepatitis, is a clinical syndrome which is diagnosed by certain clinical laboratory and histologic features compatible with the diagnosis and unexplained by a specific etiologic agent. 8 The specific features of ACAH and serological findings will be further discussed. The early typical cases were called lupoid autoimmune hepatitis because positive lupus erythematosus (LE) cells were observed with serum antinuclear antibodies and multisystem disease. 3l Classic ACAH has certain characteristics that distinguish this entity from other diseases in the CAH group. The following features are characteristic of ACAH. 27 1. Absence of markers of HBV infection. 2. High incidence in females with female/male ratio of 8:1. 3. Clinical and serological overlap within related family members. 4. Histologic lesions in liver characteristic of CAH with "piecemeal necrosis." 5. High levels of serum liver transaminase enzyme(s). 6. Very high levels of serum IgG (may be as high as 30 g/L). 7. Serum autoantibody profile that includes positive antinuclear antibody and positive smooth muscle antibody with actin specificity. Other autoantibodies as described below are observed. 8. In the variant subtype of ACAH, type 2, the autoantibody is liverkidney microsomal antibody. 9. Expression of human leucocyte antigen alleles B8 and DR3. 10. Dependency of disease remission on corticosteroid treatment.
antimitochondrial antibodies (AMA), liver-kidney microsomal antibodies, and liver membrane antibodies (LMA) are relevant diagnostic markers for diagnosis of the various autoimmune liver diseases.l'18'38'40 Autoantibodies against a liver cell membrane antigen complex (anti-LSP) have been detected in virus and non-virus-induced liver diseases. 42'43 Anti-LSP is useful to differentiate the subgroups of autoimmune liver diseases, although anti-LSP is usually absent in non-A non-B hepatitis.
rect fluorescent test. 19 In Hep-2 cells and fibroblasts, the actin cables are stained by the SMA. 2. The second type of SMA is seen in sera of almost one-third of patients with viral hepatitis. The SMA stains the intermediate filaments of fibroblasts. 3. The third type of SMA is not usually associated with liver diseases. The SMA is only positive on muscular fibers and shows a negative staining pattern using fibroblasts.
Antismooth muscle antibodies
Anticytoskeleton antibodies
Antismooth muscle antibody was identified as a specific marker for ACAH in 1965.17 SMA are found predominantly in association with classic "lupoid" ACAH and often in association with ANA. 31 The SMA in liver disease is reactive with F-actin, a constituent of the liver cell cytoskeleton in close association with the plasma membrane of the liver cell. 1° About 51)% of patients with HBsAg-negative chronic active hepatitis show high titers at anti-SMA. 1,18,38,40 Smooth muscle antibody can be detected with indirect immunofluorescence (IF) studies in stomach sections. The SMA produces a cytoplasmic fluorescent pattern on muscle fibers of the stomach and vessel walls. Low titers of SMA may be found in normal individuals and in other diseases. 55 However, an indirect IF test titer of SMA >/1:80 has diagnostic significance in lupoid ACAH.I With SMA titers of i> 1:80, the incidence of lupoid ACAH is 70%-90%. SMA titers of 1:80 have a predictive value of 30% for ACAH. 1 Heterogeneity among SMA and crossreactivity was first observed by Whittingham et a1.,59 who noted, by the indirect IF test, positive staining of renal glomerular cells, striated cells, and thymus medulla. Abuaf et a1.1 have classified three types of SMA:
Smooth muscle contains several contractible proteins in the cytoskeleton. 1'19'z°'47 The different filaments are 1) microfilaments, which include actin, myosin, troponin, tropomyosin, calmodulin, etc.; 2) intermediate filaments, which are vimentin, desmin, keratins, neurofilaments, and glial filaments; and 3) microtubules (tubulin). Anti-actin cables are present in fibroblasts and Hep-2 cells. The antiactin antibodies are seen in ACAH, primary biliary cirrhosis, and drug-induced hepatic disease. 1,15 Antibodies to the intermediate filaments vimentin, desmin, and keratin are found in viral hepatitis A-, B-, and D-induced liver diseases. 1.46,49,56 Abuaf et a1.1 concluded that the typical ACAH smooth muscle antibody has antiactin specificity that may show crossreactivity with renal glomeruli, brush border of proximal renal tubular cells, gastric parietal cells, or liver cells. This characteristic immunofluorescent pattern is best observed by routinely using three serum dilutions (1:10, 1:40, 1:160) that improve the predictive value for lupoid ACAH to 92%.1
Subgroups of ACAH Autoimmune-type chronic active hepatitis is heterogeneous. At least four different subgroups can be distinguished by serologic markers (Table 2). Antinuclear antibodies, smooth muscle antibodies, autoantibodies to soluble liver antigen,
| . The first SMA is associated with "lupoid" ACAH. The antibody reacts with renal glomeruli, brush border of the proximal renal tubule, gastric parietal cells, and liver cells with a polygonal staining pattern in the indi© 1991 Elsevier Science Publishing Co., Inc.
Anti-liver-kidney microsome antibody Anti-LKM was differentiated from antimitochondrial antibody (AMA) by Rizzetto et al. 51'52 who noted the immunofluorescent staining pattern on a liverkidney stomach block. The anti-LKM stained principally the microsome of hepatocytes and proximal renal tubules. The anti-M2 mitochondrial antibody stains the distal renal tubules where typical anti-LKM is negative. Abuaf et a1.1 reported that 10% of anti-LKM may show weak positive staining in the distal renal 0197-1859/91/$0.00 + 2.20
164 C L I N I C A L I M M U N O L O G Y Newsletter
tubules; also, some sera contain both antiM2 mitochondrial antibody and anti-LKM resulting in an intermediate immunofluorescent pattern. Confirmation of the anti-LKM may be demonstrated by 1) absorption of the positive serum with liver subcellular fraction; 2) immunodiffusion studies showing a line of identity when reacted with known positive reference sera, and 3) immunoblotting studies with specific antigen preparations. Although the anti-LKM patterns of fluorescence may be seen in a small minority of patients with other nonliver autoimmune diseases, 5 anti-LKM antibodies are generally considered highly specific for a subgroup of ACAH. 18.38.4o The LKM antibodies are seen mostly in children 1'38"45'59 and have been termed LKM-113 to distinguish them from LKM-2 antibodies, which are found in tienilic acid drug-induced hepatitis. 14 Subsequently, LKM-3 was observed in patients with chronic hepatitis delta (D) virus infection. 7 The biochemical structure of LKM-1 is cytochrome P450 dbl which is known to metabolize several drugs 34 and is expressed on the hepatoceilular membrane surface. Antibody to liver cytosol (Anti-LC-1) A new autoantibody that reacted against a soluble cytosolic antigen in liver tissue was detected by immunoprecipitation in the neurons of 21 patients with chronic active hepatitis. 39 The antibody was organ specific but not species specific and was called liver cytosol antibody type 1 (anti-LC-1). In 7 of 21 cases, no other antibody was found, and the remaining 14 cases had LKM-1. 39 With indirect immunofluorescence studies, the LC-I antibody stained the cytoplasm of hepatocytes from various animal species and spared the cellular layer around the central veins (juxtavenous hepatocytes). The distinctive immunofluorescence pattern of LC-1 antibody was observed in the seven patients who were negative for LKM-1 antibody. 39 Anti LC-1 antibody was observed in patients with chronic active hepatitis of unknown cause. Anti LC-I antibody was not present in 100 patients 0197-1859/91/$0.00 + 2.20
with ACAH with anti-actin antibody, and in patients with primary biliary cirrhosis, and drug-induced hepatitis. The LC-I antibody may be a second marker of type-2 ACAH associated with anti-LKM1. 39 One study has reported antibody incidence of 90% for anti-LKM-l (130 of 144 cases) and 25% for anti-LC-1 (36 of 144 cases). 1 Autoantibodies to soluble liver antigen Autoantibodies against SLA were demonstrated by radioimmunoassay procedure and are characteristic of a third subgroup of ACAH. 32 The SLA antibody is an important diagnostic marker since 25% of these patients lack other autoantibody markers. 32'38 The SLA antigen is found in both liver and kidney tissue and is not organ or disease specific. The SLA antigen is probably associated with liver cytokeratins 8 and 18.1'35 Mitochondrial subtype antibodies with specificity for primary biliary cirrhosis have been observed in some patients with ACAH with SLA. 35 These patients may represent an overlap syndrome between ACAH and primary biliary cirrhosis. Antimitochondrial antibodies AMA was detected by tissue immunofluorescence in the sera of primary biliary cirrhosis patients in 1965. 57 The pattern of fluorescence was a coarse granular cytoplasmic staining most prominently seen in the distal tubules of the kidney section. With the use of more sophisticated biochemical and immunoassay methods, two different target antigen subtypes of AMA have been identified in PBC. 35'38 The PBC-specific subtypes of mitochondrial antibodies are 1) against the E-2 component of the pyruvate dehydrogenase complex or 2) against the branched-chain alpha-keto acid dehydrogenase. 33"35 Nine different mitochondrial antibodies have been identified.3'4 Many of the mitochondrial antibodies are found in diseases other than autoimmune liver diseases. Liver membrane antibodies Several investigators have reported the binding of serum antibodies in liver disease patients to the surface of isolated in © 1991 Elsevier Science Publishing Co., Inc.
Vol. 11, No. I I, 1991
vitro cultured liver cells. ~5 With the u.~c of a radioimmunoassay procedure, lgG binding to the surface of isolated liver cells was observed to be due to different antigen-antibody systems. 37 Gerken et al. ~2 reported that the target of LMA is not expressed on the membranes of intact and viable hepatocytes. The LMA most likely reacts with cytoskeletal components that lie directly underneath the cell surface. The LMA probably does not have any pathogenetic significance and is related to the group of antibodies to cytoskeletal components. However, Gerken et al. ~2 concluded that LMA may be useful in the diagnosis of autoimmune diseases. Antinuclear antibodies The frequency of ANAs may be as high as 81% in ACAH, 58% in primary biliary cirrhosis, 47% in alcoholic liver disease, 37% in hepatitis B virus-associated chronic active hepatitis, 25% in liverkidney microsomal antibody-positive chronic active hepatitis, and 25% in cryptogenic cirrhosis. 6"48 The indirect immunofluorescence test generally shows a high titer of >11:80 with a homogeneous or speckled pattern. ANA with speckled patterns are usually seen in autoimmune liver disease (53%) and primary biliary cirrhosis (34%), and up to one-third of all other types of liver disease, t.54 The anticentromere was observed in 10% of cases with primary biliary cirrhosis. 5 Also, a specific-speckled multiple nuclear dot staining pattern on Hep-2 cells by indirect immunofluorescence studies was detected in sera from 17% of patients with primary biliary cirrhosis. 5 Antibodies to nuclear lamins Lamins A, B, and C, are the major proteins of the nuclear lamins which are a filamentous coating of the inner nuclear membrane. The nuclear lamins may be involved in regulation of DNA replication and gene expression. 24'58 Autoantibodies to nuclear lamins were observed in 12 of 16 cases of active "lupoid" ACAH, but not in 35 patients with the disease in remission. 58 Also, only three of 37 patients with primary biliary cirrhosis had anti-lamin antibodies.
Vol. 1 1, No. 11, 1991
Autoantibodies to nuclear lamin (limiting membrane of the nucleus) have been described in SLE, scleroderma, thrombocytopenia, neutropenia, and liver disease. 24 By I F - A N A test, the anti-lamin antibodies react with the nuclear envelope in a "rim- or ring-like" and linear staining pattern. This staining disappears during mitosis, which differentiates the anti-lamin antibodies from antibodies to DNA, or histone, which stains the chromosomes in mitotic cells. Immunoblotting studies have shown autoantibodies to lamins A, B, and C.
Autoantibodies to 200 kDa nuclear envelope protein Lozano et al. 25 reported one-half of patients with primary biliary cirrhosis had serum antibodies directed to nuclear envelope-associated proteins and this "nuclear ring-like" fluorescent pattern was highly specific for PBC. The antibody responsible for the above pattern reacted with a 200 kDa nuclear envelope polypeptide. 25 The "rim-like or ring-like" pattern of immunofluorescent sera on the indirect immunofluorescent ANA test is similar to the pattern observed with antibodies to nuclear lamins. However, the "rim-like" pattern in PBC was observed when the antibodies reacted against a 200 kDa nuclear envelope protein different from lamin proteins. 23'25 Lassoued et al. 22 have reported the nuclear ring fluorescent pattern in 25% of 180 patients with PBC, and this prevalence was similar to the 29% reported by Ruffatti et al. 53 The general agreement today is that the ring-like fluorescent pattern is not specific for PBC. However, Lozano et al. 26 showed that the ring-like fluorescence pattern in the A N A test in the absence of native anti-DNA antibodies is specific for PBC. Further, the 52.6% incidence reported by Lozano et al. 25 of ring-like fluorescence in PBC was observed when sera were tested at a high dilution of 1:400 as compared to the 1:100 screening dilution used by Lassoued et al. 22
Liver specific antibody (LSP) Antibodies to a macromolecular fraction of liver homogenate called the liver-specific proteins have been detected in a
CLINICAL IMMUNOLOGY
high percentage of patients with autoimmune liver disease. 43 However, LSP antibodies can also be seen in almost half of the patients with viral hepatitis and other liver diseases. 16.36
3.
Asialoglycoprotein receptor (ASGPR ) antibody The complex liver-specific protein antigen is one of the components in the asialoglycoprotein receptor. 4° When the asialoglycoprotein receptor was used as an antigen for antibody detection, high antibody titers were predominantly detected in sera from patients with A C A H and primary biliary cirrhosis. 44
4.
5.
6.
Acetylcholine receptor antibodies Acetylcholine receptor antibodies have been reported in significant groups of patients with primary biliary cirrhosis. El
7.
Other antibodies A significant number of patients with autoimmune liver disease have antibodies to other organ tissues such as thyroid microsomal antigens, thyroglobulin, and parietal cell antibodies. 9 Thus, there is some putative inteiTelationship of autoimmune liver disorders to the other human autoimmune diseases. These observations support the hypothesis of familial and genetic susceptibility to a generalized disorder. 3°
8.
9.
10.
Summary The significance in etiology and pathogenesis of A C A H of the many circulating autoantibodies is largely unknown. Many of the autoantibodies are useful for diagnosis and subclassification of the diseases. At the present time the predictive value of certain autoantibody markers for ACAH may be 90%. Classic " l u p o i d " ACAH is best identified by antismooth muscle antibody of the actin type. AntiLKM-1 and anti-LC-1 appear to be specific for A C A H type 2. cIN
11.
12.
13.
References 1. Abuaf N, Johanet C, Homberg JC: Autoantibodies in autoimmune chronic active hepatitis. In: Krawitt EL, Wiesner RH (eds): Autoimmune Liver Diseases, New York, Raven Press, pp. 93-109, 1991. 2. Baggenstoss AH, Soloway RD, Summerskill WHJ, et al.: Chronic active liver © 1991 Elsevier Science Publishing Co., Inc.
14.
Newsletter 165
disease--the range of histologic lesions, their response to treatment and evolution. Human Pathol 3:183-198, 1972. Berg PA, Klein R: Autoantibody patterns in primary biliary cirrhosis. In: Krawitt EL, Wiesner RH (eds.): Autoimmune Liver Diseases, New York, Raven Press, pp. 123-142, 1991. Berg PA, Klein R: Heterogeneity of antimitochondrial antibodies. Sem Liver Dis 9:103-116, 1989. Bernstein RM, Callender ME, Neuberger JM, Hughes GRV, Williams R: Anticentromere antibody in primary biliary cirrhosis. Annals Rheum Dis 41:612-614, 1982. Cassani F, Bianchi FB, Lenzi M, Volta U, Pisi E: Immunomorphological characterization of antinuclear antibodies in chronic liver disease. J Clin Pathol 38:801-805, 1985. Crivelli O, Lavarini C, Chiaberge D, et al.: Microsomal auto-antibodies in chronic infection with the HBsAg associated delta agent. Clin Exp Immunol 54:232-238, 1983. Czaja AJ: Natural history, clinical features, and treatment of autoimmune hepatitis. Sem Liver Dis 4:1-12, 1984. Doniach D, Roitt IM, Walker JG, Sherlock S: Tissue antibodies in primary biliary cirrhosis, active chronic (lupoid) hepatitis, cryptogenic cirrhosis, and other liver diseases and their clinical implications. Clin Exp Immunol 1:237, 1966. Gabbiani G, Ryan GB, Lamelin JP, et al.: Human smooth autoantibody (its identification as antiactin antibody and a study of its binding to "nonmuscular" cells). Am J Pathol 72:473--484, 1973. Galen RS, Gambrins SR (eds.): Beyond Normality: The Predictive Value and Efficiency of Medical Diagnosis. New York, John Wiley & Sons, 1975. Gerken G, Manns M, Ramadori G, Poralla T, Dienes HP, Meyer zum Buschenfelde K-H: Liver membrane autoantibodies in chronic active hepatitis: Studies on mechanically and enzymatically isolated rabbit hepatocytes. J Hepatol 5:65-74, 1987. Homberg JC, Abuaf N, Bernard O, et al.: Chronic active hepatitis associated with antiliver/kidney microsome antibody type h A second type of "autoimmune" hepatitis. Hepatology 7:1333-1339, 1986. Homberg JC, Andre C, Abuaf N: A new anti-liver-kidney microsome antibody (anti-LKM2) in tienilic acid-induced hepatitis. Clin Exp lmmunol 55:561-570, 1984. 0197-1859/91/$0.00 + 2.20
166 C L I N I C A L I M M U N O L O G Y Newsletter
15. Islam S, Mekhloufi F, Paul JM, et al.: Characteristics of clometacin-induced hepatitis with special reference to the presence of antiactin-cable antibodies. Autoimmunity 2:213-221, 1989. 16. Jensen DM, McFarlane IG, Portmann BS: Detection of antibodies directed against a liver-specific membrane lipoprotein in patients with acute and chronic active hepatitis. N Engl J Med 299:1-7, 1978. 17. Johnson GD, Holborow EJ, Glynn LE: Antibody to smooth muscle in patients with liver disease. Lancet 2:878-879, 1965. 18. Krawitt EL, Wiesner RH: Autoimmune Liver Disease. New York, Raven Press, 1991. 19. Kurki P, Miettinen A, Linder E, et al.: Different types of smooth muscle antibodies in chronic active hepatitis and primary biliary cirrhosis: Their diagnostic and prognostic significance. Gut 21:878-884. 1980. 20. Kurki P, Miettinen A, Salaspuro M, Virtanen I, Stenman S: Cytoskeleton antibodies in chronic active hepatitis, primary biliary cirrhosis and alcoholic liver disease. Hepatology 3:297-307, 1983. 21. Kyriatsoulis A, Manns M, Gerken G, et al.: Immunochemical characterization of anti-acetylcholine receptor antibodies in primary biliary cirrhosis. J Hepatol 6:283-290, 1988. 22. Lassoued K, Danon F, Andre C, Courvalin JC, Dhumeaux D: Liver disease associated with autoantibodies directed to nuclear envelope proteins. Hepatology 9:911, 1989. 23. Lassoued F, Guilly MN, Andre C, et al.: Autoantibodies to 200 kD polypeptide(s) of the nuclear envelope: A new serological marker of primary biliary cirrhosis. Clin Exp Immunol 74:283-288, 1988. 24. Lassoued K, Guilly M-N, Danon F, et al.: Antinuclear autoantibodies specific for lamins. Ann Intern Med 108:829-833, 1988. 25. Lozano F, Pares A, Borche L, et al.: Autoantibodies against nuclear envelopeassociated proteins in primary biliary cirrhosis. Hepatology 8:930-938, 1988. 26. Lozano F, Pares A, Borche L, et al.: Response to letter to editor of reference (54). Hepatology 9:912, 1989. 27. Mackay IR: Autoimmune (lupoid) hepatitis: An entity in the spectrum of chronic active liver disease. J Gastroenterol Hepatol 5:352-359, 1990. 28. Mackay IR: Chronic active hepatitis. In: Mackay IR (ed.): Frontiers of Gastrointestinal Research, Vol. l, Basel, Karger, pp. 0197-1859/91/$0.00 + 2.20
142-187, 1975. 29. Mackay IR: Pathogenesis of autoimmune chronic active hepatitis. In: Krawitt EL, Wiesner RH (eds.): Autoimmune Liver Diseases, New York, Raven Press, pp. 21-42, 1991. 30. Mackay IR, O'Brien RM, Whittingham SF, Tait BD: Autoimmune and other diseases of the liver: lmmunogenetic aspects. In: Farid N (ed.): The Immunogenetics of Autoimmune Disease, Boca Raton, FL, CRC Press, 1991. 31. Mackay IR, Taft LT, Cowling DC: Lupoid hepatitis. Lancet ii: 123-126, 1956. 32. Manns M, Gerken G, Kyriatsoulis A, et al.: Characterization of a new subgroup of autoimmune chronic active hepatitis by autoantibodies against a soluble liver antigen. Lancet I:292-294, 1987. 33. Manns M, Gerken G, Kyriatsoulis A, et al.: Two different subtypes of antimitochondrial antibodies are associated with primary biliary cirrhosis: Identification and characterization by radioimmunoassay and immunoblotting. Hepatology 7:893, 1987. 34. Manns M, Kyriatsoulis A, Amelizad Z, et al.: Relationship between the target antigen of liver-kidney microsomal (LKM) autoantibodies and rat isoenzymes of cytochrome P-450. J Clin Lab Anal 2:245248, 1988. 35. Manns M, Meyer zum Buschenfelde K-H: Nature of autoantigens and autoantibodies in autoimmune hepatitis. Springer Sem lmmunopath 12:57-65, 1990. 36. Manns M, Meyer zum Buschenfelde K-H, Hess G: Autoantibodies against LSP in acute and chronic liver diseases: Studies on organ-species- and disease-specificity. Gutt 21:955-961, 1980. 37. Manns M, Meyer zum Buschenfelde K-H, Hutteroth TH, Hess G: Detection and characterization of liver membrane autoantibodies in chronic active hepatitis by a solid-phase immunoassay. Clin Exp Immunol 42:263, 1980. 38. Manns M, Nakamura RM: Autoimmune liver disease. Clinics Lab Med 8:281301, 1988. 39. Martini E, Abuaf N, Cavalli F, Durand V, Johanet C, Homberg J-C: Antibody to liver cytosol (anti-LCl) in patients with autoimmune chronic active hepatitis type 2. Hepatology 8:1662-1666, 1988. 40. Meyer zum Buschenfelde K-H, Lohse AW, Manns M, Porall T: Autoimmunity and liver disease I. Hepatology 12:354362, 1990. 41. Meyer zum Buschenfelde K-H, Manns M: © 1991 Elsevier Science PublishingCo., Inc.
Vol. 1 1, No. 1 1, 1991
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
Immune response to liver membrane anti gens in acute and chronic hepatitis. In: Chisari FV (ed.): Advances in Hepatitis Research, New York, Masson, pp. 152162, 1984. Meyer zum Buschenfelde K-H, Manns M, Hutteroth M, et al.: LM-Ag and LSP-two different target antigens involved in the immunopathogenesis of chronic active hepatitis. Clin Exp Immunol 37:205-212, 1979. Meyer zum Buschenfelde K-H, Miescher PA: Liver specific antigens. Purification and characterization. Clin Exp lmmunol 10:89-102, 1972. McFarlane BM, McSorley CG, Vergani D, McFarlane IG, Williams R: Serum autoantibodies reacting with the hepatic asialoglycoprotein receptor protein (hepatic lectin) in acute and chronic liver disorders. J Hepatol 3:196--205, 1986. Peakman M, Lobo-Yeo A, Mieli-Vergani G, Davies ET, Mowat AP, Vergani D: Characterization of anti-liver kidney microsomal antibody in childhood autoimmune chronic active hepatitis: Evidence for lgGl subclass restriction, polyclonality and non cross-reactivity with hepatocyte surface antigens. Clin Exp Immunol 69:543-544, 1987. Pederson JS, Toh BH, Locarnini SA, Gust ID, Shyamala GNS: Autoantibody to intermediate filaments in viral hepatitis. Clin lmmunol Immunopathol 21:154-161, 1981. Pedersen JS, Toh BH, Mackay IR, et al.: Segregation of autoantibody to cytoskeletal filaments, actin and intermediate filaments with two types of chronic active hepatitis. Clin Exp Immunol 48:527-533, 1982. Penner E, Kindas-Mugge 1, Hitchman E, Sauermann G: Nuclear antigens recognized by antibodies present in liver disease sera. Clin Exp Immunol 63:428-433, 1985. Pisi E, Zauli D, Crespi C: Autoantibodies in chronic hepatitis delta virus infection. In: Rizzetto M e t al.: The Hepatitis Delta Virus and Its Infection, New York, Alan R. Liss, Inc., pp. 249-256, 1987. Popper H, Geller SA: Pathogenetic considerations in the histologic diagnosis of drug-induced injury. In: Fenoglio CM. Wolff M (eds.): Progress in Surgical Pathology, New York, Masson, pp. 233246, 1981. Rizzetto M, Bianchi FB, Doniach D: Characterization of the microsomal antigen related to a sub-class of active chronic hepatitis. Immunology 26:589-
Vol. 11, No. 1 1, 1991
590, 1974. 52. Rizzetto M, Swana G, Doniach D: Microsomal antibodies in active chronic hepatitis and other disorders. Clin Exp Immunol 15:331-334, 1973. 53. Ruffatti A, Arslan P, Floreani A, et al.: Nuclear membrane-staining antinuclear antibody in patients with primary biliary cirrhosis. J Clin Immunol 5:357-361, 1985. 54. Szostecki C, Krippner H, Penner E, Bautz FA: Autoimmune sera recognize a
8tflatlonal
C L I N I C A L I M M U N O L O G Y Newsletter 167
100 kD nuclear protein antigen (sp-100). Clin Exp Immunol 68:108-116, 1987. 55. Toh BH: Smooth muscle autoantibodies and autoantigens. Clin Exp Immunol 38:621-628, 1979. 56. Toh BH, Yildiz A, Sotelo J, et al.: Viral infections and IgM autoantibodies to cytoplasmic intermediate filaments. Clin Exp Immunol 37:76-82, 1979. 57. Walker JG, Doniach D, Roitt LM, Sherlock S: Serological tests in the diagnosis
of primary biliary cirrhosis. Lancet I:827831, 1965. 58. Wesierska-Gadek J, Penner E, Hitchman E, Sauermann G: Antibodies to nuclear lamins in autoimmune liver disease. Clinical Immunol Immunopathol 49:107-115, 1988. 59. Whittingham S, Mackay IR, Irwin J: Autoimmune hepatitis. Immunofluorescence reaction with cytoplasm of smooth muscle and renal glomerular cells. Lancet 1:1333-1335, 1966.
Autoantllmdle0
continued from page 161 nicotinic acetylcholine receptor (nAChR) at the neuromuscular junction was identified as the primary target of pathogenic autoantibodies in MG, 2'3'11A4 the focus of MG research shifted away from StrAb. Nevertheless, StrAb continue to be of clinical and research interest because of their associations with epithelial thymama, 1'4'8A°'13'16'26'32a tumor that occurs in approximately 15% of patients with MG. 2° The application in recent years of more incisive techniques for characterizing the antigenic specificities of StrAb has advanced our understanding of these unique paraneoplastic autoantibodies. StrAb are detectable in 24% of patients who have thymoma without clinical signs of MG, 24 and in 90% of patients who have both MG and thymoma. 23 Overall, approximately 30% of patients with MG have StrAb, 24 but many of these patients may have subclinical thymoma. Lennon and Howard found that the incidence of StrAb was only 12% among patients with MG who were surgically proven not to have thymoma.t° The close association of StrAb with thymoma suggests that these antibodies may arise as part of a paraneoplastic autoimmune response to a thymic tumor. Current research on StrAb is aimed at identifyng the immunogenic stimulu~ for this autoimmune response and determining the role of StrAb in MG and thymoma. An understanding of the biological significance of StrAb depends on identifying the antigens recognized by these antibodies. The location of these antigens in the striations of skeletal muscle offers some clue to their identity. The skeletal mus-
I
I sorcomem
Figure 1. Drawing of a skeletal muscle cell or fiber which contains many myofibrils. Each myofibril is composed of contractile filaments arranged in sarcomeres. The alignment of the sarcomeres in different myofibrils produces the striated appearance of the muscle cell.
cle cell contains many myofibrils, each consisting of contractile filaments arranged in sarcomeres (Figure 1). Different regions of the sarcomere contain different contractile proteins. The region containing myosin is called the A-band (anisotropic) because it appears dark
E
I
when viewed by phase-contrast microscopy. The lighter region of the sarcomere contains actin, and is called the 1-band (isotropic). The Z-disk, containing a-actinin, lies between these two regions (Figure 2). The sarcomeres in different myofibrils are aligned with one
A- Band
I
Z
~I6BmiBIK~
t
J I- Band
I
I Z - Band
Figure 2. Diagram of a sarcomere, which is bounded on each side by Z-disks containing ct-actinin. The I-band is composed of actin filaments that attach to the Z-disk. The A-band contains myosin filaments that slide between the actin filaments during muscle contraction. © 1991 Elsevier Science Publishing Co., Inc.
0197-1859/91/$0.00 + 2.20
Diagnostic Significance of Autoantibodies in A u t o l m m u n e Chronic Active Hepatitis Robert M. Nakamura Department of Pathology, Scripps Clinic and Research Foundation, California at San Diego School of Medicine, La Jolla, California
David J. Bylund Section of Transplantation Immunology, Department of Pathology, Scripps Clinic and Research Foundation, La Jolla, California
here is significant evidence for the existence of autoimmune liver disorders.lS'3S'4° These diseases are characterized by organ-specific and many non-organ-specific autoantibody markers. The autoimmune liver diseases may be broadly placed into three groups:
T
1. Primary biliary cirrhosis (PBC). 2. Autoimmune chronic active hepatitis (ACAH). 3. "Certain cases of cryptogenic cirrhosis. The autoimmune liver diseases are often associated with certain histocompati-
bility antigens [human leucocyte antigen (HLA)], such as HLA-A1, HLA-B8, and HLA-DR3, which suggest a genetic predisposition. 3° In many of the autoimmune liver disorders, the exact etiology and nature of primary insult on the parenchymal hepatic cells is unknown. The mechanism of injury may be due to cytotoxic lymphocytes which attack antigens exposed on the hepatocyte membrane. Lymphocytes recognize a, membrane antigen only if it is associated with the HLA determinants on the host membrane. 18,38,4o This report will discuss the various associated organ-specific and non-organ-
specific antibodies associated with autoimmune chronic active hepatitis. The emphasis will be placed on the diagnostic value of the various autoantibodies as well as their usefulness in prognosis.
Autoantibodies: General Overview Characteristic autoantibodies are seen in autoimmune liver diseases. The specific role of the autoantibodies in the pathogenesis and course of the diseases remains unknown, but they are of diagnostic significance. 1 In ACAH, anti-smooth muscle antibodies (SMA) and antinuclear antibodies continued on page 162
Striational Autoantibodies: Paraneoplastic Antibodies Associated w i t h Thymoma and Myasthenia Gravis Carol L. Williams and Vanda A. Lennon Neuroimmunology Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota
S
triational autoantibodies (StrAb), which bind to the contractile elements of striated muscle, were first discovered in the serum of patients with myasthenia gravis (MG) over 3 decades ago. 22 This provided the first serological evidence that MG is an autoimmune disease, and generated speculation that CIMNDC I1(I I)161-176,1991
Elsevier
antibodies might cause the muscle weakness that is characteristic of MG. Further interest in StrAb was stimulated by the observation that these antibodies also bind to epithelial and myoid cells in the thymus, s'16'23'26'27'30 indicating common antigens in muscle and thymus. After the continued on page 167 0197-1859/91/$0.00 + 2.20
162 C L I N I C A L I M M U N O L O G Y
TABLE 1.
Newsletter
Vol
AUTOANTIBODIES IN ACAH ~ (I) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
Antismooth muscle antibodies Anticytoskeletal antibodies Anti-liver-kidney microsomal antibodies Anti-liver cytosol antibodies (LC-I) Anti-soluble liver antigen antibodies Antimitochondrial antibodies Anti-liver membrane antibodies Antinuclear antibodies Antibodies to nuclear lamin Liver-specific antibody Asialoglycoprotein receptor antibody Other
From references 18, 38, and 40. (ANA) are commonly found. The l i v e r kidney microsomal (LKM) antibody characterizes a type-II subgroup o f A C A H 38 diagnosed mainly in children who are often negative for all other autoantibodies. Another subgroup of A C A H is characterized by antibodies against a soluble liver antigen (SLA). 32 There are many mitochondrial antibodies associated with various liver and other diseases. 4 Primary biliary cirrhosis (PBC) is almost always associated with specific antimitochondrial antibodies. Mitochondrial antibodies are occasionally observed in A C A H . However, A C A H is characteristically associated with a variety of autoantibodies, listed in Table 1, The autoantibodies associated with the subgroups of A C A H are shown in Table 2. The S M A , A N A , L K M , and A M A antibodies can be diagnosed by an indirect immunofluorescent method. HowTABLE 2.
ever, anti-SLA is detected by an immunoblotting or radioimmunoassay method. ~,38
General Diagnostic Value of Autoantibodies The predictive value of the various tests for autoantibodies is dependent upon the prevalence of the disease, t 1 The predictive value of a test with a sensitivity of 100% and a specificity of 99% is only 0.1% if the disease has a prevalence of 1 in 100,000.1 In one European study, the incidence o f classical A C A H and A C A H type 2 with L K M antibodies was 2.2 and 0.5 per 100,000, respectively. 13
Chronic Active Hepatitis ( C M t ) and Autoimmune Chronic Active Hepatitis Autoimmune hepatitis was described during the 1950s as an entity called chronic active hepatitis. 28 Chronic active hepati-
1 1, No. 1 1, 199 1
tis is diagnosed by clinical and histological findings. The characteristic "~hallmark" lesion of CAH is piecemeal necrosis (PN), which is characterized by a prominent lymphohistiocytic infiltrate causing liver cell necrosis at periportal and/or paraseptal mesenchymal/parenchymal junctions. -~'5° PN, although characteristic of A C A H , is not pathognomic, being seen also in viral and drug-associated chronic hepatitis, primary biliary cirrhosis, alcohol-induced liver disease, W i l s o n ' s disease, and alpha-l-anti-trypsin deficiency. 29'41"5° PN may progress to bridging necrosis with fibrosis and eventually irreversible cirrhosis. Lymphocytic piecemeal necrosis is best explained as an immune attack against the periportal and paraseptal hepatocytes. The most likely target antigen would be in the surface membranes of hepatocytes. Direct immunofluorescence studies have shown that IgG is detected in a linear pattern on the hepatocyte surface membrane, z9 Classification of C A H Mackay has classified C A H into several groups of different or unknown etiologies. 18,29,38,40 1. CAH-A: autoimmune. 2. CAH-B: hepatitis B virus (HBV) and hepatitis D (HDV) virus. 3. CAH-C: cryptogenic (autoantibody negative), hepatitis B surface antigen (HBsAg) negative. 4. CAH-D: drug induced, that is, oxyphenisatin and methyldopa.
AUTOIMMUNE CHRONIC ACTIVE HEPATITIS SUBGROUPS a
Antibody
Classic "Lupoid"
SMA Antibody Positive
LKM Antibody Positive
SLA Antibody Positive
ANA SMA SLA AMA LKM LMA
+ + +
+ +/-
+ -
+ /+ +/+ /-
a Fromreferences18.38, and 40.
5. CAH-E: ethanol induced. 6. CAH-N: unknown virus other than hepatitis A, B, or C. CAH-B cases usually have H B s A G in the blood. Hepatitis D virus (delta agent) is associated with hepatitis B as a coinfection. Many of the cases of the cryptogenic group can now be attributed to infection with hepatitis C virus (HCV).
CLINICAL IMMUNOLOGY NEWSLE'ITER (ISSN 0197-1859) is issued monthly in one indexed volume per year by Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010. Subscription price per year: $125.00. For surface airlift add $37.00. Second-class postage paid at New York, NY, and at additional mailing offices. P U l m u t ~ : Send address changes to Clinical Immunology Newsletter, Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010. NOTE: No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use of operation of any methods, products, inst~ctions for ideas contained in the material herein. No suggested test or procedure should be carried out unless, in the reader's judgment, its risk is justified. Because of rapid advances in the medical sciences, we recommend that the independent verification of diagnoses and drug dosages should be made. Discussions, views and recommendations as to medical procedures, choice of drugs and drug dosages are the responsibility of the authors.
0197-1859/91/$0.00 + 2.20
© 1991 Elsevier Science Publishing Co., Inc.
C L I N I C A L I M M U N O L O G Y Newsletter 163
Vol. 11, No. 11, 1991
Classic ACAH or "Lupoid Autoimmune Hepatitis" The CAH-A group, or classic autoimmune chronic active hepatitis, is a clinical syndrome which is diagnosed by certain clinical laboratory and histologic features compatible with the diagnosis and unexplained by a specific etiologic agent. 8 The specific features of ACAH and serological findings will be further discussed. The early typical cases were called lupoid autoimmune hepatitis because positive lupus erythematosus (LE) cells were observed with serum antinuclear antibodies and multisystem disease. 3l Classic ACAH has certain characteristics that distinguish this entity from other diseases in the CAH group. The following features are characteristic of ACAH. 27 1. Absence of markers of HBV infection. 2. High incidence in females with female/male ratio of 8:1. 3. Clinical and serological overlap within related family members. 4. Histologic lesions in liver characteristic of CAH with "piecemeal necrosis." 5. High levels of serum liver transaminase enzyme(s). 6. Very high levels of serum IgG (may be as high as 30 g/L). 7. Serum autoantibody profile that includes positive antinuclear antibody and positive smooth muscle antibody with actin specificity. Other autoantibodies as described below are observed. 8. In the variant subtype of ACAH, type 2, the autoantibody is liverkidney microsomal antibody. 9. Expression of human leucocyte antigen alleles B8 and DR3. 10. Dependency of disease remission on corticosteroid treatment.
antimitochondrial antibodies (AMA), liver-kidney microsomal antibodies, and liver membrane antibodies (LMA) are relevant diagnostic markers for diagnosis of the various autoimmune liver diseases.l'18'38'40 Autoantibodies against a liver cell membrane antigen complex (anti-LSP) have been detected in virus and non-virus-induced liver diseases. 42'43 Anti-LSP is useful to differentiate the subgroups of autoimmune liver diseases, although anti-LSP is usually absent in non-A non-B hepatitis.
rect fluorescent test. 19 In Hep-2 cells and fibroblasts, the actin cables are stained by the SMA. 2. The second type of SMA is seen in sera of almost one-third of patients with viral hepatitis. The SMA stains the intermediate filaments of fibroblasts. 3. The third type of SMA is not usually associated with liver diseases. The SMA is only positive on muscular fibers and shows a negative staining pattern using fibroblasts.
Antismooth muscle antibodies
Anticytoskeleton antibodies
Antismooth muscle antibody was identified as a specific marker for ACAH in 1965.17 SMA are found predominantly in association with classic "lupoid" ACAH and often in association with ANA. 31 The SMA in liver disease is reactive with F-actin, a constituent of the liver cell cytoskeleton in close association with the plasma membrane of the liver cell. 1° About 51)% of patients with HBsAg-negative chronic active hepatitis show high titers at anti-SMA. 1,18,38,40 Smooth muscle antibody can be detected with indirect immunofluorescence (IF) studies in stomach sections. The SMA produces a cytoplasmic fluorescent pattern on muscle fibers of the stomach and vessel walls. Low titers of SMA may be found in normal individuals and in other diseases. 55 However, an indirect IF test titer of SMA >/1:80 has diagnostic significance in lupoid ACAH.I With SMA titers of i> 1:80, the incidence of lupoid ACAH is 70%-90%. SMA titers of 1:80 have a predictive value of 30% for ACAH. 1 Heterogeneity among SMA and crossreactivity was first observed by Whittingham et a1.,59 who noted, by the indirect IF test, positive staining of renal glomerular cells, striated cells, and thymus medulla. Abuaf et a1.1 have classified three types of SMA:
Smooth muscle contains several contractible proteins in the cytoskeleton. 1'19'z°'47 The different filaments are 1) microfilaments, which include actin, myosin, troponin, tropomyosin, calmodulin, etc.; 2) intermediate filaments, which are vimentin, desmin, keratins, neurofilaments, and glial filaments; and 3) microtubules (tubulin). Anti-actin cables are present in fibroblasts and Hep-2 cells. The antiactin antibodies are seen in ACAH, primary biliary cirrhosis, and drug-induced hepatic disease. 1,15 Antibodies to the intermediate filaments vimentin, desmin, and keratin are found in viral hepatitis A-, B-, and D-induced liver diseases. 1.46,49,56 Abuaf et a1.1 concluded that the typical ACAH smooth muscle antibody has antiactin specificity that may show crossreactivity with renal glomeruli, brush border of proximal renal tubular cells, gastric parietal cells, or liver cells. This characteristic immunofluorescent pattern is best observed by routinely using three serum dilutions (1:10, 1:40, 1:160) that improve the predictive value for lupoid ACAH to 92%.1
Subgroups of ACAH Autoimmune-type chronic active hepatitis is heterogeneous. At least four different subgroups can be distinguished by serologic markers (Table 2). Antinuclear antibodies, smooth muscle antibodies, autoantibodies to soluble liver antigen,
| . The first SMA is associated with "lupoid" ACAH. The antibody reacts with renal glomeruli, brush border of the proximal renal tubule, gastric parietal cells, and liver cells with a polygonal staining pattern in the indi© 1991 Elsevier Science Publishing Co., Inc.
Anti-liver-kidney microsome antibody Anti-LKM was differentiated from antimitochondrial antibody (AMA) by Rizzetto et al. 51'52 who noted the immunofluorescent staining pattern on a liverkidney stomach block. The anti-LKM stained principally the microsome of hepatocytes and proximal renal tubules. The anti-M2 mitochondrial antibody stains the distal renal tubules where typical anti-LKM is negative. Abuaf et a1.1 reported that 10% of anti-LKM may show weak positive staining in the distal renal 0197-1859/91/$0.00 + 2.20
164 C L I N I C A L I M M U N O L O G Y Newsletter
tubules; also, some sera contain both antiM2 mitochondrial antibody and anti-LKM resulting in an intermediate immunofluorescent pattern. Confirmation of the anti-LKM may be demonstrated by 1) absorption of the positive serum with liver subcellular fraction; 2) immunodiffusion studies showing a line of identity when reacted with known positive reference sera, and 3) immunoblotting studies with specific antigen preparations. Although the anti-LKM patterns of fluorescence may be seen in a small minority of patients with other nonliver autoimmune diseases, 5 anti-LKM antibodies are generally considered highly specific for a subgroup of ACAH. 18.38.4o The LKM antibodies are seen mostly in children 1'38"45'59 and have been termed LKM-113 to distinguish them from LKM-2 antibodies, which are found in tienilic acid drug-induced hepatitis. 14 Subsequently, LKM-3 was observed in patients with chronic hepatitis delta (D) virus infection. 7 The biochemical structure of LKM-1 is cytochrome P450 dbl which is known to metabolize several drugs 34 and is expressed on the hepatoceilular membrane surface. Antibody to liver cytosol (Anti-LC-1) A new autoantibody that reacted against a soluble cytosolic antigen in liver tissue was detected by immunoprecipitation in the neurons of 21 patients with chronic active hepatitis. 39 The antibody was organ specific but not species specific and was called liver cytosol antibody type 1 (anti-LC-1). In 7 of 21 cases, no other antibody was found, and the remaining 14 cases had LKM-1. 39 With indirect immunofluorescence studies, the LC-I antibody stained the cytoplasm of hepatocytes from various animal species and spared the cellular layer around the central veins (juxtavenous hepatocytes). The distinctive immunofluorescence pattern of LC-1 antibody was observed in the seven patients who were negative for LKM-1 antibody. 39 Anti LC-1 antibody was observed in patients with chronic active hepatitis of unknown cause. Anti LC-I antibody was not present in 100 patients 0197-1859/91/$0.00 + 2.20
with ACAH with anti-actin antibody, and in patients with primary biliary cirrhosis, and drug-induced hepatitis. The LC-I antibody may be a second marker of type-2 ACAH associated with anti-LKM1. 39 One study has reported antibody incidence of 90% for anti-LKM-l (130 of 144 cases) and 25% for anti-LC-1 (36 of 144 cases). 1 Autoantibodies to soluble liver antigen Autoantibodies against SLA were demonstrated by radioimmunoassay procedure and are characteristic of a third subgroup of ACAH. 32 The SLA antibody is an important diagnostic marker since 25% of these patients lack other autoantibody markers. 32'38 The SLA antigen is found in both liver and kidney tissue and is not organ or disease specific. The SLA antigen is probably associated with liver cytokeratins 8 and 18.1'35 Mitochondrial subtype antibodies with specificity for primary biliary cirrhosis have been observed in some patients with ACAH with SLA. 35 These patients may represent an overlap syndrome between ACAH and primary biliary cirrhosis. Antimitochondrial antibodies AMA was detected by tissue immunofluorescence in the sera of primary biliary cirrhosis patients in 1965. 57 The pattern of fluorescence was a coarse granular cytoplasmic staining most prominently seen in the distal tubules of the kidney section. With the use of more sophisticated biochemical and immunoassay methods, two different target antigen subtypes of AMA have been identified in PBC. 35'38 The PBC-specific subtypes of mitochondrial antibodies are 1) against the E-2 component of the pyruvate dehydrogenase complex or 2) against the branched-chain alpha-keto acid dehydrogenase. 33"35 Nine different mitochondrial antibodies have been identified.3'4 Many of the mitochondrial antibodies are found in diseases other than autoimmune liver diseases. Liver membrane antibodies Several investigators have reported the binding of serum antibodies in liver disease patients to the surface of isolated in © 1991 Elsevier Science Publishing Co., Inc.
Vol. 11, No. I I, 1991
vitro cultured liver cells. ~5 With the u.~c of a radioimmunoassay procedure, lgG binding to the surface of isolated liver cells was observed to be due to different antigen-antibody systems. 37 Gerken et al. ~2 reported that the target of LMA is not expressed on the membranes of intact and viable hepatocytes. The LMA most likely reacts with cytoskeletal components that lie directly underneath the cell surface. The LMA probably does not have any pathogenetic significance and is related to the group of antibodies to cytoskeletal components. However, Gerken et al. ~2 concluded that LMA may be useful in the diagnosis of autoimmune diseases. Antinuclear antibodies The frequency of ANAs may be as high as 81% in ACAH, 58% in primary biliary cirrhosis, 47% in alcoholic liver disease, 37% in hepatitis B virus-associated chronic active hepatitis, 25% in liverkidney microsomal antibody-positive chronic active hepatitis, and 25% in cryptogenic cirrhosis. 6"48 The indirect immunofluorescence test generally shows a high titer of >11:80 with a homogeneous or speckled pattern. ANA with speckled patterns are usually seen in autoimmune liver disease (53%) and primary biliary cirrhosis (34%), and up to one-third of all other types of liver disease, t.54 The anticentromere was observed in 10% of cases with primary biliary cirrhosis. 5 Also, a specific-speckled multiple nuclear dot staining pattern on Hep-2 cells by indirect immunofluorescence studies was detected in sera from 17% of patients with primary biliary cirrhosis. 5 Antibodies to nuclear lamins Lamins A, B, and C, are the major proteins of the nuclear lamins which are a filamentous coating of the inner nuclear membrane. The nuclear lamins may be involved in regulation of DNA replication and gene expression. 24'58 Autoantibodies to nuclear lamins were observed in 12 of 16 cases of active "lupoid" ACAH, but not in 35 patients with the disease in remission. 58 Also, only three of 37 patients with primary biliary cirrhosis had anti-lamin antibodies.
Vol. 1 1, No. 11, 1991
Autoantibodies to nuclear lamin (limiting membrane of the nucleus) have been described in SLE, scleroderma, thrombocytopenia, neutropenia, and liver disease. 24 By I F - A N A test, the anti-lamin antibodies react with the nuclear envelope in a "rim- or ring-like" and linear staining pattern. This staining disappears during mitosis, which differentiates the anti-lamin antibodies from antibodies to DNA, or histone, which stains the chromosomes in mitotic cells. Immunoblotting studies have shown autoantibodies to lamins A, B, and C.
Autoantibodies to 200 kDa nuclear envelope protein Lozano et al. 25 reported one-half of patients with primary biliary cirrhosis had serum antibodies directed to nuclear envelope-associated proteins and this "nuclear ring-like" fluorescent pattern was highly specific for PBC. The antibody responsible for the above pattern reacted with a 200 kDa nuclear envelope polypeptide. 25 The "rim-like or ring-like" pattern of immunofluorescent sera on the indirect immunofluorescent ANA test is similar to the pattern observed with antibodies to nuclear lamins. However, the "rim-like" pattern in PBC was observed when the antibodies reacted against a 200 kDa nuclear envelope protein different from lamin proteins. 23'25 Lassoued et al. 22 have reported the nuclear ring fluorescent pattern in 25% of 180 patients with PBC, and this prevalence was similar to the 29% reported by Ruffatti et al. 53 The general agreement today is that the ring-like fluorescent pattern is not specific for PBC. However, Lozano et al. 26 showed that the ring-like fluorescence pattern in the A N A test in the absence of native anti-DNA antibodies is specific for PBC. Further, the 52.6% incidence reported by Lozano et al. 25 of ring-like fluorescence in PBC was observed when sera were tested at a high dilution of 1:400 as compared to the 1:100 screening dilution used by Lassoued et al. 22
Liver specific antibody (LSP) Antibodies to a macromolecular fraction of liver homogenate called the liver-specific proteins have been detected in a
CLINICAL IMMUNOLOGY
high percentage of patients with autoimmune liver disease. 43 However, LSP antibodies can also be seen in almost half of the patients with viral hepatitis and other liver diseases. 16.36
3.
Asialoglycoprotein receptor (ASGPR ) antibody The complex liver-specific protein antigen is one of the components in the asialoglycoprotein receptor. 4° When the asialoglycoprotein receptor was used as an antigen for antibody detection, high antibody titers were predominantly detected in sera from patients with A C A H and primary biliary cirrhosis. 44
4.
5.
6.
Acetylcholine receptor antibodies Acetylcholine receptor antibodies have been reported in significant groups of patients with primary biliary cirrhosis. El
7.
Other antibodies A significant number of patients with autoimmune liver disease have antibodies to other organ tissues such as thyroid microsomal antigens, thyroglobulin, and parietal cell antibodies. 9 Thus, there is some putative inteiTelationship of autoimmune liver disorders to the other human autoimmune diseases. These observations support the hypothesis of familial and genetic susceptibility to a generalized disorder. 3°
8.
9.
10.
Summary The significance in etiology and pathogenesis of A C A H of the many circulating autoantibodies is largely unknown. Many of the autoantibodies are useful for diagnosis and subclassification of the diseases. At the present time the predictive value of certain autoantibody markers for ACAH may be 90%. Classic " l u p o i d " ACAH is best identified by antismooth muscle antibody of the actin type. AntiLKM-1 and anti-LC-1 appear to be specific for A C A H type 2. cIN
11.
12.
13.
References 1. Abuaf N, Johanet C, Homberg JC: Autoantibodies in autoimmune chronic active hepatitis. In: Krawitt EL, Wiesner RH (eds): Autoimmune Liver Diseases, New York, Raven Press, pp. 93-109, 1991. 2. Baggenstoss AH, Soloway RD, Summerskill WHJ, et al.: Chronic active liver © 1991 Elsevier Science Publishing Co., Inc.
14.
Newsletter 165
disease--the range of histologic lesions, their response to treatment and evolution. Human Pathol 3:183-198, 1972. Berg PA, Klein R: Autoantibody patterns in primary biliary cirrhosis. In: Krawitt EL, Wiesner RH (eds.): Autoimmune Liver Diseases, New York, Raven Press, pp. 123-142, 1991. Berg PA, Klein R: Heterogeneity of antimitochondrial antibodies. Sem Liver Dis 9:103-116, 1989. Bernstein RM, Callender ME, Neuberger JM, Hughes GRV, Williams R: Anticentromere antibody in primary biliary cirrhosis. Annals Rheum Dis 41:612-614, 1982. Cassani F, Bianchi FB, Lenzi M, Volta U, Pisi E: Immunomorphological characterization of antinuclear antibodies in chronic liver disease. J Clin Pathol 38:801-805, 1985. Crivelli O, Lavarini C, Chiaberge D, et al.: Microsomal auto-antibodies in chronic infection with the HBsAg associated delta agent. Clin Exp Immunol 54:232-238, 1983. Czaja AJ: Natural history, clinical features, and treatment of autoimmune hepatitis. Sem Liver Dis 4:1-12, 1984. Doniach D, Roitt IM, Walker JG, Sherlock S: Tissue antibodies in primary biliary cirrhosis, active chronic (lupoid) hepatitis, cryptogenic cirrhosis, and other liver diseases and their clinical implications. Clin Exp Immunol 1:237, 1966. Gabbiani G, Ryan GB, Lamelin JP, et al.: Human smooth autoantibody (its identification as antiactin antibody and a study of its binding to "nonmuscular" cells). Am J Pathol 72:473--484, 1973. Galen RS, Gambrins SR (eds.): Beyond Normality: The Predictive Value and Efficiency of Medical Diagnosis. New York, John Wiley & Sons, 1975. Gerken G, Manns M, Ramadori G, Poralla T, Dienes HP, Meyer zum Buschenfelde K-H: Liver membrane autoantibodies in chronic active hepatitis: Studies on mechanically and enzymatically isolated rabbit hepatocytes. J Hepatol 5:65-74, 1987. Homberg JC, Abuaf N, Bernard O, et al.: Chronic active hepatitis associated with antiliver/kidney microsome antibody type h A second type of "autoimmune" hepatitis. Hepatology 7:1333-1339, 1986. Homberg JC, Andre C, Abuaf N: A new anti-liver-kidney microsome antibody (anti-LKM2) in tienilic acid-induced hepatitis. Clin Exp lmmunol 55:561-570, 1984. 0197-1859/91/$0.00 + 2.20
166 C L I N I C A L I M M U N O L O G Y Newsletter
15. Islam S, Mekhloufi F, Paul JM, et al.: Characteristics of clometacin-induced hepatitis with special reference to the presence of antiactin-cable antibodies. Autoimmunity 2:213-221, 1989. 16. Jensen DM, McFarlane IG, Portmann BS: Detection of antibodies directed against a liver-specific membrane lipoprotein in patients with acute and chronic active hepatitis. N Engl J Med 299:1-7, 1978. 17. Johnson GD, Holborow EJ, Glynn LE: Antibody to smooth muscle in patients with liver disease. Lancet 2:878-879, 1965. 18. Krawitt EL, Wiesner RH: Autoimmune Liver Disease. New York, Raven Press, 1991. 19. Kurki P, Miettinen A, Linder E, et al.: Different types of smooth muscle antibodies in chronic active hepatitis and primary biliary cirrhosis: Their diagnostic and prognostic significance. Gut 21:878-884. 1980. 20. Kurki P, Miettinen A, Salaspuro M, Virtanen I, Stenman S: Cytoskeleton antibodies in chronic active hepatitis, primary biliary cirrhosis and alcoholic liver disease. Hepatology 3:297-307, 1983. 21. Kyriatsoulis A, Manns M, Gerken G, et al.: Immunochemical characterization of anti-acetylcholine receptor antibodies in primary biliary cirrhosis. J Hepatol 6:283-290, 1988. 22. Lassoued K, Danon F, Andre C, Courvalin JC, Dhumeaux D: Liver disease associated with autoantibodies directed to nuclear envelope proteins. Hepatology 9:911, 1989. 23. Lassoued F, Guilly MN, Andre C, et al.: Autoantibodies to 200 kD polypeptide(s) of the nuclear envelope: A new serological marker of primary biliary cirrhosis. Clin Exp Immunol 74:283-288, 1988. 24. Lassoued K, Guilly M-N, Danon F, et al.: Antinuclear autoantibodies specific for lamins. Ann Intern Med 108:829-833, 1988. 25. Lozano F, Pares A, Borche L, et al.: Autoantibodies against nuclear envelopeassociated proteins in primary biliary cirrhosis. Hepatology 8:930-938, 1988. 26. Lozano F, Pares A, Borche L, et al.: Response to letter to editor of reference (54). Hepatology 9:912, 1989. 27. Mackay IR: Autoimmune (lupoid) hepatitis: An entity in the spectrum of chronic active liver disease. J Gastroenterol Hepatol 5:352-359, 1990. 28. Mackay IR: Chronic active hepatitis. In: Mackay IR (ed.): Frontiers of Gastrointestinal Research, Vol. l, Basel, Karger, pp. 0197-1859/91/$0.00 + 2.20
142-187, 1975. 29. Mackay IR: Pathogenesis of autoimmune chronic active hepatitis. In: Krawitt EL, Wiesner RH (eds.): Autoimmune Liver Diseases, New York, Raven Press, pp. 21-42, 1991. 30. Mackay IR, O'Brien RM, Whittingham SF, Tait BD: Autoimmune and other diseases of the liver: lmmunogenetic aspects. In: Farid N (ed.): The Immunogenetics of Autoimmune Disease, Boca Raton, FL, CRC Press, 1991. 31. Mackay IR, Taft LT, Cowling DC: Lupoid hepatitis. Lancet ii: 123-126, 1956. 32. Manns M, Gerken G, Kyriatsoulis A, et al.: Characterization of a new subgroup of autoimmune chronic active hepatitis by autoantibodies against a soluble liver antigen. Lancet I:292-294, 1987. 33. Manns M, Gerken G, Kyriatsoulis A, et al.: Two different subtypes of antimitochondrial antibodies are associated with primary biliary cirrhosis: Identification and characterization by radioimmunoassay and immunoblotting. Hepatology 7:893, 1987. 34. Manns M, Kyriatsoulis A, Amelizad Z, et al.: Relationship between the target antigen of liver-kidney microsomal (LKM) autoantibodies and rat isoenzymes of cytochrome P-450. J Clin Lab Anal 2:245248, 1988. 35. Manns M, Meyer zum Buschenfelde K-H: Nature of autoantigens and autoantibodies in autoimmune hepatitis. Springer Sem lmmunopath 12:57-65, 1990. 36. Manns M, Meyer zum Buschenfelde K-H, Hess G: Autoantibodies against LSP in acute and chronic liver diseases: Studies on organ-species- and disease-specificity. Gutt 21:955-961, 1980. 37. Manns M, Meyer zum Buschenfelde K-H, Hutteroth TH, Hess G: Detection and characterization of liver membrane autoantibodies in chronic active hepatitis by a solid-phase immunoassay. Clin Exp Immunol 42:263, 1980. 38. Manns M, Nakamura RM: Autoimmune liver disease. Clinics Lab Med 8:281301, 1988. 39. Martini E, Abuaf N, Cavalli F, Durand V, Johanet C, Homberg J-C: Antibody to liver cytosol (anti-LCl) in patients with autoimmune chronic active hepatitis type 2. Hepatology 8:1662-1666, 1988. 40. Meyer zum Buschenfelde K-H, Lohse AW, Manns M, Porall T: Autoimmunity and liver disease I. Hepatology 12:354362, 1990. 41. Meyer zum Buschenfelde K-H, Manns M: © 1991 Elsevier Science PublishingCo., Inc.
Vol. 1 1, No. 1 1, 1991
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
Immune response to liver membrane anti gens in acute and chronic hepatitis. In: Chisari FV (ed.): Advances in Hepatitis Research, New York, Masson, pp. 152162, 1984. Meyer zum Buschenfelde K-H, Manns M, Hutteroth M, et al.: LM-Ag and LSP-two different target antigens involved in the immunopathogenesis of chronic active hepatitis. Clin Exp Immunol 37:205-212, 1979. Meyer zum Buschenfelde K-H, Miescher PA: Liver specific antigens. Purification and characterization. Clin Exp lmmunol 10:89-102, 1972. McFarlane BM, McSorley CG, Vergani D, McFarlane IG, Williams R: Serum autoantibodies reacting with the hepatic asialoglycoprotein receptor protein (hepatic lectin) in acute and chronic liver disorders. J Hepatol 3:196--205, 1986. Peakman M, Lobo-Yeo A, Mieli-Vergani G, Davies ET, Mowat AP, Vergani D: Characterization of anti-liver kidney microsomal antibody in childhood autoimmune chronic active hepatitis: Evidence for lgGl subclass restriction, polyclonality and non cross-reactivity with hepatocyte surface antigens. Clin Exp Immunol 69:543-544, 1987. Pederson JS, Toh BH, Locarnini SA, Gust ID, Shyamala GNS: Autoantibody to intermediate filaments in viral hepatitis. Clin lmmunol Immunopathol 21:154-161, 1981. Pedersen JS, Toh BH, Mackay IR, et al.: Segregation of autoantibody to cytoskeletal filaments, actin and intermediate filaments with two types of chronic active hepatitis. Clin Exp Immunol 48:527-533, 1982. Penner E, Kindas-Mugge 1, Hitchman E, Sauermann G: Nuclear antigens recognized by antibodies present in liver disease sera. Clin Exp Immunol 63:428-433, 1985. Pisi E, Zauli D, Crespi C: Autoantibodies in chronic hepatitis delta virus infection. In: Rizzetto M e t al.: The Hepatitis Delta Virus and Its Infection, New York, Alan R. Liss, Inc., pp. 249-256, 1987. Popper H, Geller SA: Pathogenetic considerations in the histologic diagnosis of drug-induced injury. In: Fenoglio CM. Wolff M (eds.): Progress in Surgical Pathology, New York, Masson, pp. 233246, 1981. Rizzetto M, Bianchi FB, Doniach D: Characterization of the microsomal antigen related to a sub-class of active chronic hepatitis. Immunology 26:589-
Vol. 11, No. 1 1, 1991
590, 1974. 52. Rizzetto M, Swana G, Doniach D: Microsomal antibodies in active chronic hepatitis and other disorders. Clin Exp Immunol 15:331-334, 1973. 53. Ruffatti A, Arslan P, Floreani A, et al.: Nuclear membrane-staining antinuclear antibody in patients with primary biliary cirrhosis. J Clin Immunol 5:357-361, 1985. 54. Szostecki C, Krippner H, Penner E, Bautz FA: Autoimmune sera recognize a
8tflatlonal
C L I N I C A L I M M U N O L O G Y Newsletter 167
100 kD nuclear protein antigen (sp-100). Clin Exp Immunol 68:108-116, 1987. 55. Toh BH: Smooth muscle autoantibodies and autoantigens. Clin Exp Immunol 38:621-628, 1979. 56. Toh BH, Yildiz A, Sotelo J, et al.: Viral infections and IgM autoantibodies to cytoplasmic intermediate filaments. Clin Exp Immunol 37:76-82, 1979. 57. Walker JG, Doniach D, Roitt LM, Sherlock S: Serological tests in the diagnosis
of primary biliary cirrhosis. Lancet I:827831, 1965. 58. Wesierska-Gadek J, Penner E, Hitchman E, Sauermann G: Antibodies to nuclear lamins in autoimmune liver disease. Clinical Immunol Immunopathol 49:107-115, 1988. 59. Whittingham S, Mackay IR, Irwin J: Autoimmune hepatitis. Immunofluorescence reaction with cytoplasm of smooth muscle and renal glomerular cells. Lancet 1:1333-1335, 1966.
Autoantllmdle0
continued from page 161 nicotinic acetylcholine receptor (nAChR) at the neuromuscular junction was identified as the primary target of pathogenic autoantibodies in MG, 2'3'11A4 the focus of MG research shifted away from StrAb. Nevertheless, StrAb continue to be of clinical and research interest because of their associations with epithelial thymama, 1'4'8A°'13'16'26'32a tumor that occurs in approximately 15% of patients with MG. 2° The application in recent years of more incisive techniques for characterizing the antigenic specificities of StrAb has advanced our understanding of these unique paraneoplastic autoantibodies. StrAb are detectable in 24% of patients who have thymoma without clinical signs of MG, 24 and in 90% of patients who have both MG and thymoma. 23 Overall, approximately 30% of patients with MG have StrAb, 24 but many of these patients may have subclinical thymoma. Lennon and Howard found that the incidence of StrAb was only 12% among patients with MG who were surgically proven not to have thymoma.t° The close association of StrAb with thymoma suggests that these antibodies may arise as part of a paraneoplastic autoimmune response to a thymic tumor. Current research on StrAb is aimed at identifyng the immunogenic stimulu~ for this autoimmune response and determining the role of StrAb in MG and thymoma. An understanding of the biological significance of StrAb depends on identifying the antigens recognized by these antibodies. The location of these antigens in the striations of skeletal muscle offers some clue to their identity. The skeletal mus-
I
I sorcomem
Figure 1. Drawing of a skeletal muscle cell or fiber which contains many myofibrils. Each myofibril is composed of contractile filaments arranged in sarcomeres. The alignment of the sarcomeres in different myofibrils produces the striated appearance of the muscle cell.
cle cell contains many myofibrils, each consisting of contractile filaments arranged in sarcomeres (Figure 1). Different regions of the sarcomere contain different contractile proteins. The region containing myosin is called the A-band (anisotropic) because it appears dark
E
I
when viewed by phase-contrast microscopy. The lighter region of the sarcomere contains actin, and is called the 1-band (isotropic). The Z-disk, containing a-actinin, lies between these two regions (Figure 2). The sarcomeres in different myofibrils are aligned with one
A- Band
I
Z
~I6BmiBIK~
t
J I- Band
I
I Z - Band
Figure 2. Diagram of a sarcomere, which is bounded on each side by Z-disks containing ct-actinin. The I-band is composed of actin filaments that attach to the Z-disk. The A-band contains myosin filaments that slide between the actin filaments during muscle contraction. © 1991 Elsevier Science Publishing Co., Inc.
0197-1859/91/$0.00 + 2.20