Complement and host defense against infection

T H E J O U R N A L OF

PEDIATRICS F E B R U A R Y 1977

Volume 90

Number 2

MEDICAL PROGRESS

Complement and host defense against infection Richard B. Johnston, Jr., M.D.,* and Robert M. Stroud, M.D., Birmingham, Ala.

K N o w LED G E of the biochemistry and physiology of the complement system has grown dramatically in recent years. Understanding of the function of complement and application of this understanding to the care of patients have been greatly improved by the careful evaluation of human beings and animals with disorders of this system. In its essence, this new knowledge clearly indicates that the complement system is one of the principal mediators of the inflammatory response and, thereby, serves an essential function in host defense against infection. After a brief review of the biochemistry and physiology of complement as background, we will attempt to summarize current knowledge that relates to the activity of this system in resistance to infection.

From the Departments of Pediatrics and Microbiology, The Division of Clinical Immunology and Rheumatology, Department of Medicine, and The Comprehensive Cancer Center, University of Alabama Medical Center. Supported by United States Public Health Service grants AI 10286, CA 16673, CA 13148, HL 11310, and pro/ect 8197-01, V.A. Hospital Dr. Johnston was a Josiah Mac):, Jr. Foundation Faculty Scholar at The Rockefeller University, New York, when this manuscript was written. *Reprint address: Department of Pediatrics, University of Alabama Medical Center, Birmingham, A L 35294.

NOMENCLATURE The subject of complement may appear more complex than it actually is because of its cryptic nomenclature. Its terminology is reasonably logical, however, and consists of only a few simple rules: Each component has been assigned a number in the order of its discovery and is preceded by the letter C. Unfortunately, the first four components do not interact in the sequence in which they were discovered, but rather in the order C1423. The

See related article, p. 180.

Abbreviations used CRP: C-reactive protein CoVF: cobra-venom factor SLE: systemic lupus erythematosus LPS: lipopolysaccharide PMN: polymorphonuclear leukocyte remaining components react in the appropriate numerical order, C56789. CI has three s u b c o m p o n e n t s - C l q , Clr, C Is. Fragments of components resulting from cleavage by other components acting as enzymes are assigned small letters (a, b, c, or d); with the exception of C2 fragments, the smaller piece that is released into surrounding fluids is assigned the letter "a," and the major part of the molecule, bound to other components or to some part of the

VoL 90, No. 2, pp. 169-179

17 0

The Journal of Pediatrics February 1977

Johnston and Stroud

THE COMPLEMENT SYSTEM

Alternative

Clossieol

olysocchorides

"C-kinin"

C4o

EA"~l~-*~q~EACT

EACI~,

f

Properdin Foctor D Foctor B

C~

Adherence

C~b ~mplificotion

~ C ~O Anophylotoxin

EACI423b Immune ~,,~o,,~c~ Phogocy/osis Adherence Binding fo B cells (C3b,C3d)

C5o Anophylotomin

EC5~9 c~gECS"-~EACI-Sb

Chemo/oxis

Cyto/ysis C567 Reoetion with 8ystonderCells Chemotoxis

Fig. 1, Sequence of activation of the complement components of the classical pathway and interaction with the properdin system. E = Erythrocyte (could stand for any antigen); A = antibody; C-CRP = C carbohydrate-C-reactive protein; C1 (C3b) Ina = CI (C3b) inactivator; LPS = lipopolysaccharide; CoVF = cobra-venom factor.

immune complex, is assigned "b," e.g., C3a and C3b. When a component is activated (becomes an active enzyme), a bar is placed above it, e.g., (2]. Components of the alternative (properdin) pathway have been assigned letters in the place of former trivial names: B was previously referred to as C3 proactivator (C3PA) or glycine-rich beta glycoprotein (GBG); D was previously termed precursor of C3PA convertase or proGBGase; and P is now used for properdin. All of these have active forms denoted as B, D, and P. BASIC PRECEPTS Certain principles are basic to the understanding of complement function: 1. Complement is a system of interacting proteins. The biologic functions of the system depend upon the interaction of individual components. 2. The components interact in an orderly, sequential fashion. This has been referred to as "cascade," in analogy to the clotting system, in that activation of each component (except the first) depends upon activation of the prior component or components in the sequence. 3. Interaction occurs along two pathways: what is now termed the classical pathway, in which the components interact in the order antigen-antibody-C142356789; and the more recently discovered alternative, or properdin pathway, in the order activator-(antibody)-properdin system-C356789. Whether antibody is required and what

the exact sequence of interaction of components is in the alternative pathway are not clearly understood, as we shall discuss. These pathways interact with each other and with the clotting and kallikrein systems. 4. The interaction of the early-acting components (C14235) is enzymatic in nature, so that "activation" refers to transformation of the component into an active enzyme. In contrast, the interaction between C5b, C6, C7. C8, and C9 is nonenzymatic through noncovalent, probably hydrophobic, bonds. In the case of C 1, activation is a result of its interaction with antibody. Activation of C4, C2, C3, C5, as well as of factor B of the alternative pathway, is secondary to cleavage by a preceding component or components. Thus, activation of early components generates an enzyme which fixes to the antigen-antibodycomplement complex and catalyzes a reaction on the next component, whereas later-acting components (C6 to C9) adsorb to the complex or the underlying cell by an interaction which depends on a change in their configuration. These basic principles can be illustrated by a more detailed analysis of the activation sequence. SEQUENCE

OF ACTIVATION

The sequence in which complement components interact and the chemical and functional by-products of those reactions are schematized in Fig. 1. E stands for erythrocyte and A for antibody to the erythrocyte: this has

Volume 90 Number 2

been the standard in vitro system used to study the classical pathway reaction; but other antigens fixing IgG or lgM antibody could substitute for EA, e.g., soluble and insoluble immune complexes or antibody-sensitized bacteria, viruses, or tumor cells. The classical pathway begins by fixation of C 1, by way of Clq, to the backbone (the Fc, nonantigen-binding part) of the antibody molecule. Recent work indicates that Creactive protein, known for many years to be elevated in certain inflammatory states, may substitute for antibody in the fixation of Clq. That is, CRP that has reacted with "C carbohydrate" from microorganisms can substitute for antigen-antibody and initiate reaction of the entire sequence. ',~ Thus, CRP functions like antibody though it can combine with only a few specific "antigens" and its molecular weight (ca 120,000 daltons compared to 150,000 daltons for IgG) and structure (five or six identical subunits) are quite different? This reaction has the potential of playing the important biologic role of initiating inflammation in the absence of antibody. In the next two steps polypeptide fragments are split from C4 and C2 during their activation and fixation by the enzymatic action of CT It has been thought that one of these may be a kinin-tike peptide that can induce vascular permeability, and thereby edema, through direct action on postcapillary venules.'. ~ Fixation of the major part of the molecule, C4b, to the complex endows it with the capacity to adhere to a variety of mammalian cells, including neutrophils, monocytes, and primate erythrocytes, which is the phenomenon termed "immune adherence.'"; Cleavage of C3 and generation of C3b is the next step in the sequence and the most crucial in terms of biologic activity. C3 cleavage can be achieved through antibodyCI'i~ (the classical pathway "C3 convertase") or through a second system of interacting enzymes, the alternative pathway. C3b is essential to the function of the latter as a subunit or modulator of key enzymes, as discussed below. Once fixed to the complex, C3b permits adherence of the complex to cells with C3b receptors, namely, B lymphocytes, mammalian erythrocytes, and phagocytic cells (neutrophils, monocytes, macrophages). In the last case, phagocytosis occurs. In fact, without C3 bound to the cell (microorganism), phagocytosis, especially by neutrophils, is very inefficient in vitro; and judging from the propensity to severe pyogenic infections in C3-deficient patients, phagocytosis in vivo is also inefficient without C3. (The serum protein C3b inactivator [C3b Ina] has been reported to rapidly cleave bound C3b to a somewhat smaller molecule which has unofficially been termed "C3bC '~ Generation of C3b + appears to be required to promote phagocytosis of at least some particles?) With

Complement and host defense

17 1

time C3b is cleaved by C3b Ina to C3c, which is released, and C3d, which stays bound. Binding to B lymphocytes can occur through bound C3d as well as C3b. 9 The peptide C3a, generated when C3 is acted upon by either pathway, has "anaphylatoxin" activity, in that it reacts with mast cells to release the chemical mediators of immediate hypersensitivity, including histamine. This same peptide, or what may be another product of C3 cleavage with very similar physicochemical properties, serves as a chemical attractant to phagocytic cells. The action of C423 on C5 releases C5a, a second "anaphylatoxin"; this same peptide or a peptide of similar size and chemical structure generated during the same cleavage is the most active of the complement-derived chemotactic factors. The "membrane-attack" sequence leading to cytolysis begins with the attachment of C5b to the C423 -activating enzyme. C6 is bound to C5b without being cleaved, stabilizing the activated C5b fragment. The C5b6 complex then dissociates from C423 and reacts with C7. C5b67 complexes must attach to the cell membrane promptly or lose their activity and remain in the fluid phase, where they are believed to exert chemotactic activity. C8 binds to C5b67, and this allows C9 to bind. The assembled C5b6789 complex is inserted into the cell membrane, and lysis ensues.* Control mechanisms act at several points to prevent the system from consuming itself in unnecessary activity. An alpha-2-globulin, C I inactivator (C1 Ina), inhibits Cls esterolytic activity and, thus, the cleavage of C4 and C2. Activated C2 has a half-life of about eight minutes at 37~ and this relative instability limits the effective life of C42 and C423. The alternative pathway C3 convertase, C3bBb, also has a short half-life, although this can be prolonged by properdin. Serum contains the protein "anaphylatoxin inactivator," an enzyme with carboxypeptidase B activity, that cleaves the carboxy-terminal arginine from both C3a and C5a, thereby eliminating their biologic activities. C3b inactivator cleaves C3b, C4b, and, perhaps, C5b into inactive fragments. Absence of this protein or of C1 inactivator results in severe disease, as described below. ALTERNATIVE

(PROPERDIN)

PATHWAY

Basic aspects of the reaction s e q u e n c e o f the alternative pathway and its interaction with the classical pathway are diagrammed in Fig. 2. More specific details of this reaction have been proposed, but most of these remain to be proved. The current level of understanding of this *A more thorough review of both classical and alternative pathway interactions and more complete bibliographiesof primary work may be

found in references4 to 6.

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Johnston and Stroud

The .Imr

ALTERNATIVE COMPLEMENT PATHWAY Polysocehorides

Igs

o7 ) _

~c3

/P)C3bBb. /

;

I "%/

/

~" C3a anaphylatoKin

AgC5 - 9 ~ A g ( Ab)C5-'b-B-b(P) Cytolysis

CSo EnhancedPhogocylosis Anolphylofoxin Immune odheronce Chemotoxls Bindingto B cells (C3b,C3d)

Fig. 2. Interaction of components of the alternative (properdin) complement pathway. Ab = Antibody. (Other abbreviations are described in the legend for Fig. 1 and the text.)

Table I. Complement activities in host defense against infection Components or fragments

C14, C1423 C3a, C5a C3 and C5 fragments, C567 C3b C3b, C3d C3b

C3b C3 cleavage product C5 C 1~6 (?additional components) C1 ~9

Functional activity

Virus neutralization "Anaphylatoxin" (capillary dilatation) Chemotaxis of PMNs, monocytes, eosinophils Opsonization Enhanced induction of antibody formation Enhancement of antibodydependent cellular cytotoxicity Stimulation of B-cell lymphokine production Induction of granulocytosis Opsonization of fungi Endotoxin inactivation Lysis of viruses, virusinfected cells, tumor cells, mycoplasma, protozoa, spirochetes, and bacteria

of Pediatrics February 1977

pathway, however, is sufficient to emphasize its biologic importance. The pathway is initiated by polysaccharide and lipopolysaccharide antigens or aggregated immunoglobulin (IgA has been best studied in this regard), which interact with factors not yet defined, apparently including a protein termed "initiating factor."'" Antibody (even relatively nonspecific, cross-reacting, "natural" antibody) interacting with the antigen may be required for or may amplify the activation step, at least for some antigens."-'~ A by-pass route requiring C 1 or C Is but not C4 or C2 has also been described. ~..... The result of these interactions appears to be conversion of properdin and D to their active forms,'P and D (Fig. 2). Generation of D is followed by a cleavage activation of B in the presence of Mg* ' and either C3b or cobra-venom factor. (The latter is an altered form of cobra C3, probably C3b. TM A major fragment Bb and a minor fragment Ba are formed. The complex C3bBb (or CoVFBb) becomes an alternative pathway C3 convertase; the active enzymatic site is part of Bb. The proteolytic enzymes plasmin, trypsin, or pronase can substitute for D in this reaction. '~ P or P can bind to C3bBb, and increase the stability and efficiency of the enzyme, 1..... at least in part by protecting C3b from inactivation by C3b Ina.'" It is clear that the properdin system can be activated by C3b that has been generated through classical pathway activity, perhaps through activation of thrombin or plasmin during blood coagulation, through leukocyte proteases released by degranulation, or through trypsin in vitro. Once formed, C3b stimulates the generation of more C3b through an "amplification loop" (Fig. 1). The "loop" is modulated by the removal of bound C3b by C3b inactivator. It is not clear how the system can be activated independently of C3b generation through one of these routes. In any case, significant activation of C3 does occur through this pathway, and the resultant biologic activities are qualitatively the same as those achieved through activation by C142, as illustrated in Fig. 2. ACTIVITIES

IN H O S T

DEFENSE

Specific activities of the complement system in host defense against infection are summarized in Table I. Enhancement of the neutralization of antibody-coated viruses can be achieved with C 1 and C4.='" When antibody concentrations are low, the fixation of C3b through the classical or alternative pathway is needed tbr improved neutralization; C5 and C6 add little to the effectS'-~:: Thus complement may be particularly important in the early phases of a viral infection when antibody is limited. Antibody and fresh serum (presumably complement) can

Volume 90 Number 2

also eliminate infectivity of at least some viruses, with the production of typical "holes" in the virus, as seen by electron microscopys ~ Animal RNA tumor viruses appear to interact directly with human C l q in the absence of antibody with resulting activation of the classical pathway and lysis of the virusS" This may be a natural resistance mechanism that limits the infectivity of these viruses in man. C3a and C5a can bind to mast cells and thereby trigger release of histamine leading to vasodilatation and to the tumor and rubor of inflammation. These same or physicochemically similar fragments from C3 and C5 induce influx of neutrophils (PMNs), monocytes, and eosinophils, all of which can efficiently phagocytize microorganisms coated with C3b. Recent work suggests that the role of C3b in enhancement of phagocytosis (opsonization) may be one primarily of effecting attachment of the particle to the phagocyte, whereas the ingestion event itself may be triggered by binding of the Fc portion of antibody to a complementary chemical structure, the "Fc receptor," on the cell.-'..... Inactivation of cell-bound C3b by cleavage to C3d removes its opsonizing activity, at least for most phagocytic cellss ..... A similar functional relationship between Fc and C3b receptors seems to pertain to the phenomenon (presently identified only in vitro) of antibody-dependent cellular cytotoxicity. In this system lymphoid cells (K, or killer cells) bind to antibody-coated target cells through the K-cell Fc receptor. Such binding is required for target-cell lysis, but cytolysis is enhanced if C3b is also present on the target cell.:"' The complement system may be involved in certain aspects of B- and T-lymphocyte-mediated specific immunity: Binding of C3b- and C3d-coated particles to B lymphocytes can be shown in vitro," and this could relate to experiments showing a requirement for C3 in the generation of antibody to at least certain antigenss :'~ C3b can stimulate B cells to produce a soluble lymphokine which is a chemotactic factor for monocytes# ' Finally, genes regulating serum hemolytic complement activity in mice, C3 levels in mice, and factor B, C2, C4, and C8 levels in human beings are linked to genes located in the major histocompatibility complex, which controls antigens and functions concerned with immune recognition. It is interesting, therefore, that human peripheral blood lymphocytes and lymphoid cells maintained in culture for several years have been reported to bear C4 on their plasma membranesS' Antibody to C4 inhibits the expected replication of these lymphocytes on exposure to "foreign" cells in the mixed lymphocyte reaction, suggesting that membrane C4 plays a role in the recognition phase of the immune responseS'

Complement and host defense

I73

A cleavage product, presently undefined, that is generated from C3 when it is acted upon in vitro by C 1427 ~'or from C3 or C5 by intravascular activation of the properdin pathway with inulin or cobra-venom factor, :.~ has the property of inducing granulocytosis. A preliminary report has appeared indicating that activation of serum C3, in particular through the properdin pathway, generates a factor (or factors) that increases the spreading and phagocytic capacity of macrophages. ~; C5 promotes the phagocytosis of yeast ........ and may further boost the phagocytosis of C3-coated bacteria to a slight extent."" '' Neutralization of endotoxin in vitro and protection from its lethal effects in experimental animals requires later-acting complement components, at least through C67 ..... Finally, activation of the entire complement sequence leads to lysis of virusess virus-infected cells," tumor cells?." mycoplasma, ~" protozoa, '~-''' spirochetes, '; and most strains of bacteria. The importance of complement bactericidal activity to host defense has been questionable,.'" but the occurrence of neisserial infections in patients lacking later-acting components (see below) may indicate some role for bacteriolysis in the elimination of at least certain bacteria. CONGENITAL DEFECTS CLASSICAL PATHWAY

OF THE

Congenital deficiencies of all but the ninth component have been described (Table II). Although not all of these have been associated with increased susceptibility to infection, we feel it important that all be discussed in order that a balanced picture of complement activity be presented. Clq deficiency has occurred in association with severe combined immunodeficiency disease and other hypogammagloublinemic disorders ....... ; serum C l q concentrations were restored to normal in four patients with such disorders who underwent bone marrow transplantation? ~ Deficiency or defective activity of C 1 inactivator, whether hereditary (hereditary angioedema) :'~`or acquired in association with lymphoma,:" leads to uncontrolled C~s activity with breakdown of C4 and C2 and release of a vasoactive peptide (kinin) from one or both of these substrates. The result is episodic, localized edema. Patients with Clr, ~....... C2,:' ...... and C4 ...... ~ deficiency have had a strikingly high incidence of vasculitis syndromes, including typical systemic lupus erythematosus, an SLE-like syndrome, chronic nephritis, dermatomyositis, or Henoch-Sch6nlein purpura. Two patients with hereditary C 1 lna deficiency and SLE also have been reported. ":~ Heterozygous C2 deficiency with approximately half normal serum levels of C2 has been described in nine individuals who had an SLE syndrome or rheu-

! 74

Johnston and Stroud

7+heJournal of Pediatrics February 1977

Table 1I. Genetic complement deficiencies: Classical pathway

Deficient component

I Inheritance* ]

Clq Clr C1 Ina C4 C2

AR, ?XLR ?ACD AD ?ACD ACD

C3

ACD

C5 ACD C5 (dysfunc- ?AD fion) C6 ACD C7

ACD

C8

ACD

Associated clinical findings~f

SCID,hypogammaglobulinemia CGN, SLE syndrome Angioedema, SLE SLE syndrome SLE syndrome, MPGN, H-S purpura, dermatomyositis, infections rarely Pyogenic infections, absence of expected neutrophilia Pyogenic infections, SLE Pyoderma, septicemia, Leiner disease Gonococcal, meningococcal infections Raynaud phenomenon, sclerodactyly Disseminated gonococcal infection, SLE syndrome

*AR = Autosomalrecessive; XLR = X-linked recessive; ACD ~ autosomalc.o-dominant(heterozygoteshaveapproximatelyhalf-normalserum levels); AD = autosomal dominant; ? = mode of inheritance is unproved. ]'SCID = Severe combined immunodeficiencydisease; CGN = chronic glomerulonephritis; SLE = systemic lupus erythematosus; MPGN= membranoproliferativeglomerulonephritis;H-S = Henoch-Sch6nlein.

matoid arthritis.'+...... The reason for the concurrence of complement component deficiencies and these "collagenvascular" diseases is not known; but, if these diseases originate as infections, the association might occur-as a result of absence of one or more of the host defense properties described in ]'able I. Complement activity facilitates elimination of immune complexes ........ ; inefficiency of this process is a possible alternative or additional explanation. Genes directing complement component levels and genes influencing the immune response to specific antigens are probably closely linked on the same chromosome+v; thus it is also possible that a defect in complement could be associated with another defect in immunity that would predispose to an "autoimmune" disease. Whatever its explanation+ the frequency of the association makes it important that total complement activity be studied in patients with such disorders. Two patients with C2 deficiency have had repeated lifethreatening septicemic illnesses:'~. +; but most have not had problems with infections, presumably because of the protective function of the alternative pathway. A depression of factor B levels to about 50% of normal can occur in conjunction with C2 deficiency,;.......... however, and individuals with deficiency of both proteins might be in particular jeopardy.

Since C3 can be activated by C 142 or by the alternative pathway, a defect in the function of either pathway can be compensated to at least some extent. Without C3, however, the chemotactic fragments from C3 and C5 are not generated and opsonization of bacteria is inefficient.+.............. One would expect trouble from organisms that must be well opsonized in order to be cleared, and this has been the case: Congenital absence of C3 has been associated with recurrent, severe pyogenic infections such as pneumococcal pneumonia and meningococcal meningitisY'-~' One patient with C3 deficiency made antibody normally to several types of antigens,+:' which raises doubts as to the necessity for B lymphocyte-C3 binding in the normal antibody response. Two of the three C3deficient patients who have been adequately evaluated had sluggish neutrophilic responses to infectiony'-~' in agreement with the reports cited earlier that a cleavage factor of C3 elicits neutrophilia,:~:~.:''+ perhaps through a direct effect on the marrow.:':, The most recently reported patient with C3 deficiency, a 34-month-old boy, has not yet had problems with infection but had an episode of fever, rash, and arthralgia for two months prior to diagnosis, emphasizing the broad spectrum of clinical presentations shown by complement-deficient patientsS' A girl who has homozygous C5 deficiency has been found. She developed classical SLE in late childhood and has had a lifelong history of recurrent pyogenic infections, presumably because of the absence of the critical chemotactic factor split from C57 ~Generation of chemotaxis by her serum in vitro was markedly depressedY ~ Infants have been described with Leiner disease (generalized seborrheic dermatitis, severe diarrhea, and recurrent local and systemic infections due to enteric bacteria and staphylococci) and dysfunction of C5 manifested by decreased serum opsonization of yeast and generation of chemotactic activity5~. TM Sera from these infants had normal hemolytic complement activity, but purified C5 from one patient was abnormally labile in that hemolytic and chemotactic factor-generating activity declined rapidly on storage at 4~ ~'' An 18-year-old woman with congenital C6 deficiency has not had an unusual history of infections except for two episodes of gonococcal arthritis. ~' A second C6-deficient patient has had meningococcal meningitis that relapsed twice after proper antibiotic therapy, a distinctly unusual occurrence.~-' Each patient's serum generated chemotactic activity normally, raising doubts as to the importance of the C567 complex as a mediator of chemotaxis. Two patients with C7 deficiency have been described: One was a woman with Raynaud phenomenon and sclerodactyly~:~; the second was a healthy 13-year-old boy whose serum contained an inactivator of C7. ~' A woman with C8 deficiency had prolonged disseminated gonococcal infec-

Volume 90 Number 2

tion on two or three occasionsY' A second woman with C8 deficiency developed an SLE syndrome at 37 years of ageY Three more patients with complete C8 deficiency have not had unusual symptoms, although two partially deficient (heterozygous) individuals from their family had xeroderma pigmentosumY The possibility exists that the neisserial infections that have occured in patients with C6 or C8 deficiency could be due to lack of serum bacteriolysis or some undiscovered activity of these components, but detection of more individuals with such deficiencies will be required in order to place this possibility in proper perspective. DEFECTS OF THE ALTERNATIVE PATHWAY The first defect of the properdin pathway to be identified as such was originally reported as a deficiency of C3 secondary to its hypercatabolism."..... The patient had suffered an incredible number of severe pyogenic infections of the sort seen with congenital C3 deficiency or agammaglobulinemia. More recent studies indicate that his primary deficiency is that of C3b inactivator, an essential regulator of the alternative pathway. This deficiency permits prolonged circulation of C3b that results in constant activation of the alternative pathway and cleavage of more C3 to C3b in circular fashion, as illustrated in Fig. 2. Intravenous infusion of plasma ~''' or purified C3b inactivator~'''induced a prompt rise in serum C3 concentration and a return to normal of C3-dependent in vitro functions such as opsonization. A second type of hypercatabolic C3 deficiency has been diagnosed in children and adults with partial lipodystrophy?" "-' The pathogenesis of this C3 disorder appears to depend upon the presence of a C3-cleaving "nephritic factor" in the sera of these patientsY~ This 6S globulin, first detected in sera from individuals with chronic membranoproliferative glomerulonephritis,"' activates the alternative pathway, which consumes C3. Seventeen of the 21 lipodystrophic patients analyzed in a recent series had abnormally low serum C3 concentrations"~; 14 of these 17 had detectable serum C3-cleaving activity. Pyogenic infections including meningitis occurred in one woman with a total C3 serum value of 8 mg/dl ( < 10% of normal)"'; other patients, all of whom have had C3-cleaving activity, have had membranoproliferative nephritis."-' It is not known whether the lipodystrophy is a cause or a result of the nephritic factor-C3 disorder; clearly, it is an important marker. Newborn infants are known to have mild-to-moderate deficiencies of most complement components and may have defective whole complement hemolytic activityr especially if one examines the rate at which lysis occurs.'"' Some newborn infants have deficient opsonization

Complement and host defense

!75

Table IlL Complement deficiencies: Alternative (properdin) pathway Primary deficiency

Disease or condition

Associated clinical findings Pyogenic infections

Factor B, ?

Hypercatabolism of C3 Hypercatabolism of C3 with NeF* Newborn infants

?

Sickle cell disease

C3b Ina

Pyogenic infections, MPGN, PLDt Bacterial infections (susceptibility) Pyogenic infections (susceptibility)

*NeF = Nephriticfactor. tPLD = Partiallipodystrophy.

through the alternative complement pathway ~':-~'~; this was associated with low factor B levels in one study?': Another study showed significantly depressed factor B concentrations in over half of the cord sera tested.'' Individuals with sickle cell disease have normal classical pathway activity, but some patients have a defect in serum opsonization of pneumococci or zymosan (yeast cell walls) through the alternative pathway." ......... Defects of alternative pathway activity in other systems have also been reported, ~........ including bacteriolysis and opsonization of salmonellae,"~:~.'"' but not in the conversion of C3 by the carbohydrate inulin. '''~ Small amounts of fresh control serum will restore normal activity to deficient sera in vitro.'"" In spite of the analysis of properdin, ~........: factor B, ''''-''':~ "'" factor D,'"" '"~ and C3'""- '":' in patients' sera, the deficient factor(s) has not been identified with certainty. Defective alternative pathway function has also been shown in a few splenectomized individuals by a kinetic technique ..... '"~' but not in an assay of opsonization. 1''' Cause-and-effect relationships have not been established between the defective properdin pathway and the susceptibility to pneumococcal infections that exist in sickle cell disease and after splenectomy. This association must be demonstrated before any in vitro abnormality can be considered to have clinical significance. Nevertheless, the particularly high incidence of pneumococcal problems in infants from these two populations might have been predicted by current concepts of the role of the alternative pathway in host defense; namely, that this pathway serves as a reserve mechanism by which the critical component C3 can be activated when levels of specific antibody are insufficient to permit full activation of the classical pathway. CONCLUSIONS Because of the essential nature of the complement system in host defense against infection, a defect of

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Johnston and Stroud

complement function should be considered in any patient with an unusual pattern or frequency of infections or with collagen-vascular disease. The frequency with which complement disorders are being detected in such patients by an abnormality of the relatively simple hemolytic complement assay argues strongly that this procedure should be available as a screening test to every physician. As more defects are detected and carefully characterized, important information should be gained regarding the functions of the complement system in the maintenance of health and the mediation of disease. We are indebted to Drs. Carden Johnston, Rebecca Buckley, and Richard Hong for helpful criticisms. REFERENCES

1. Kaplan MH, and Volanakis JE: Interaction of C-reactive protein complexes with the complement system. I. Consumption of human complement associated with the reaction of C-reactive protein with pneumococcal C-polysaccharide and with the choline phosphatides, lecithin and sphingomyelin, J lmmunol 112:2135, 1974. 2. Siegel J, Rent R, and Gewurz H: Interactions of C-reactive protein with the complement system. I. Protamine-induced consumption of complement in acute phase sera, J Exp Med 140:631, 1974. 3. Gotschlich EC, and Edelman GM: C-reactive protein: A molecule composed of subunits+ Proc Natl Acad Sci USA 54:558, 1965. 4. Mayer MM: The complement system, Sci Am 229:54, 1973. 5. Volanakis JE: The human complement system, J Oral PathoI 4:195, 1975. 6. M~iller-Eberhard HJ: Complement, Ann Rev Biochem 44:697, 1975. 7. Gitlin JD, Rosen FS, and Lachmann PJ: The mechanism of action of the C3b inactivator (conglutinogen-activating factor) on its naturally occurring substrate, the major fragment of the third component of complement (C3b), J Exp Med 141:1221, 1975. 8. Stossel TP, Field RJ, Gitlin JD, Alper CA, and Rosen FS: The opsonic fragment of the third component of human complement (C3), J Exp Med 141:1329, 1975. 9. Ross GD, Polley MJ, Rabellino EM, and Grey HM: Two different complement receptors on human lymphocytes: One specific for C3b and one specific for C3b inactivatorcleaved C3b, J Exp Med 138:798, 1973. 10. Medicus RG, Schreiber RD, G0tze O, and MiJllerEberhard H J: A molecular concept of the properdin pathway, Proc Natl Acad Sci USA 73:612, 1976. 11. Sandberg AL, and Osier AG: Dual pathways of complement interaction with guinea pig immunoglobulins, J lmmunol 107:1268, 1971. 12. Winkelstein JA, Shin HS, and Wood WB Jr: Heat labile opsonins to pneumococcus. Iii. The participation of immunoglobulin and of the alternate pathway of C3 activation, J Immunol 108:1681, 1972. 13. Polhill RB Jr, Pruitt KM, and Johnston RB Jr: Demonstration of a requirement for antibody in the alternative complement pathway, Pediatr Res 10:392, 1976.

The Journal o]" Pediatrics f~,hrua O" 1977

14. May JE, and Frank MM: Hemolysis of sheep erythrocytes in guinea pig serum deficient in the fourth component of complement. II. Evidence for involvement of C I and components of the alternate complement pathway+ J Immunol 111:1668, 1973. 15. Volanakis JE, Schultz DR, and Stroud RM: Evidence that Cls participates in the alternative complement pathway, Int Arch Allergy Appl Immunol 50:68, 1976. 16. Alper CA, and Balavitch D: Cobra venom factor: Evidence for its being altered cobra C3 (the third component of complement), Science 191:1275, 1976. 17. Brade V, Nicholson A, Biner-Suermann D, and Hadding U: Formation of the C3-cleaving properdin enzyme on zymosan: Demonstration that factor D is replaceable by proteolytic enzymes, J lmmunol 113:1735, 1974. 18. Fearon DT, and Austen KF: Properdin: Initiation of alternative complement pathway, Proc Natl Acad Sci USA 72:3220, 1975. 19. Medicus RG, GOtze O, and Miiller-Eberhard H J: Alternative pathway of complement: Recruitment of precursor properdin by the labile C3/C5 convertase and the potentiation of the pathway, J Exp Med (in press). 20. Daniels CA, Borsos T, Rapp H J, Snyderman R, and Notkins AL: Neutralization of sensitized virus by purified components of complement, Proc Natl Acad Sci USA 65:528, 1970. 21. Oldstone MBA, Cooper NR, and Larson DL: Formation and biologic role of polyoma virus-antibody complexes: a critical role for complement, J Exp Med 140:549, 1974. 22. Daniels CA, Sandberg AL, and Notkins AL: Neutralization of herpes simplex virus by the alternate complement pathway, Fed Proc 34:853, 1975. 23. Leddy JP, Simons SL, and Douglas RG: Effect of selective complement deficiency on the rate of neutralization of enveloped viruses by human sera, J Immunol (in press). 24. Berry DM, and Almeida JD: The morphological and biological effects of various antisera on avian infectious bronchitis virus, J Gen Virol 3:97, 1968. 25. Welsh RM Jr, Cooper NR, Jensen FC, and Oldstone MBA: Human serum lyses RNA tumour viruses, Nature 257:612, 1975. 26. Mantovani B, Rabinovitch M, and Nussenzweig V: Phagocytosis of immune complexes by macrophages: Different roles of the macrophage receptor sites for complement (C3) and for immunoglobulin (IgG), J Exp Med 135:780, 1972. 27. Scribner D J, and Fahrney D: Neutrophil receptors for IgG and complement: Their roles in the attachment and ingestion phases of phagocytosis, J tmmunol 116:892, 1976. 28. Griffin FM, Bianco C, and Silverstein SC: Characterization of the macrophage receptor for complement and demonstration of its functional independence from the receptor for the Fc portion of immunoglobulin G, J Exp Med 141:1269, 1975. 29. Wellek B, Hahn HH, and Opferkuch W: Evidence for macrophage C3d-receptor active in phagocytosis, J Immunol 114:1643, 1975. 30. Perlmann P, Perlmann H, and Miiller-Eberhard H J: Cytolytic lymphocytic cells with complement receptor in human blood: Induction of cytolysis by IgG antibody but not by target cell-bound C3, J Exp Med 141:287. 1975.

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NK, Good RA, Jersild C, and Fotino M: Mixed lymphocyte culture determinants and C2 deficiency: LD-7a associated with C2 deficiency in four families, J Exp Med 142:495, 1975. Johnston RB Jr, Feigin RD, and Polhill RB Jr: Recurrent septicemia in a child with hereditary C2 deficiency (in preparation). Johnston RB Jr, Klemperer MR, Alper CA, and Rosen FS: The enhancement of bacterial phagoeytosis by serum: The role of complement components and two cofactors, J Exp Med 129:1275, 1969. Stossel TP, Alper CA, a n d Rosen FS: Serum-dependent phagocytosis of paraffin oil emulsified with bacterial lipopolysaccharide, J Exp Med 137:690, 1973. Alper CA, Colten HR, Rosen FS, Rabson AR, Macnab GM, and Gear ~JSS: Homozygous deficiency of C3 in a patient with repeated infections, Lancet 2:1179, 1972. Ballow M, Shira JE, Harden L, Yang SY, and Day NK: Complete absence of the third component of complement, J Clin Invest 56:703, 1975. Alper CA, Colten HR, Gear JSS, Rabson AR, and Rosen FS: Homozygous human C3 deficiency: The role of C3 in antibody production, Cis-induced vasopermeability and cobra venom-induced passive hemolysis, J Clin Invest 57:222, 1976. Alper CA, and Rosen FS: The role of complement in vivo as revealed by genetic defects, in Brent L, and Holborrow J, editors: Progress in immunology If, vol 1, New York, 1974, American Elsevier Publishing Company, p 201. Osofsky SG, Thompson BH. Lint TF, and Gewurz H: Hereditary deficiency of the third component of complement in a child with fever, skin rash and arthralgias, and response to whole blood transfusion, J PEDtATR (in press). Rosenfeld SI, Kelly ME. and Leddy JP: Hereditary deficiency of the fifth component of complement in man. I. Clinical, immunochemical, and family studies, J Clin Invest 57:1626, 1976. Rosenfeld SI, Baum J, Steigbigel RT, and Leddy JP: Hereditary deficiency of the fifth component of complement in man. II. Biological properties of C5-deficient human serum, J Clin Invest 57:1635, 1976. Miller ME, and Nilsson UR: A familial deficiency of the phagocytosis-enhancing activity of serum related to a dysfunction of the fifth component of complement (C5), N Engl J Med 282:354, 1970. Jacobs JC, and Miller ME; Fatal familial Leiner's disease: A deficiency of the opsonic activity of serum complement, Pediatrics 49:225, 1972. Nilsson UR, Miller ME, and Wyman S: A functional abnormality of the fifth component of complement (C5) from human serum of individuals with a familial opsonic defect, J Immunol 112:1164, 1974. Leddy JP, Frank MM, Gaither T, Baum J, and Klemperer MR: Hereditary deficiency of the sixth component of complement in man. I. Immunochemical, biologic, and family studies, J Clin Invest 53:544, 1974. Lim D, Gewurz A, Lint TF, Ghaze M, Sepheri B, and Gewurz H: Absence of the sixth component of complement in a patient with repeated episodes of meningococcal meningitis, J PEDIATR 89:42. 1976~

The Journal of Pediatrics February 1977

83. Boyer JT, Gall EP, Norman ME. Nilsson UR, and Zimmerman TS: Hereditary deficiency of the seventh component of complement, J Clin Invest 56:905, 1975. 84. Wellek B, and Opferkuch W: A case of deficiency of the seventh component of complement in man: Biological properties of a C7-deficient serum and description of a C7-inactivating principle. Clin Exp Immunol 19:223, 1975. 85. Petersen BH, Graham JA, and Brooks GF: Human deficiency of the eighth component of complement: The requirement of C8 for serum Neisseria gonorrhoeae bactericidal activity, J Clin Invest 57:283. 1976. 86. Jasin HE: Absence of the eighth component of complement and systemic lupus erythematosus-like disease, in Abstracts, American Rheumatology Society, 1976, p 37. 87. Day NK, Degos L, Beth E, Sassportes M, Gharbi R, and Giraldo G: C8 deficiency in a family with xeroderma pigmentosum: Lack of linkage to the HLA region, in Abstracts, First International Symposium on HLA and Disease, 1976, p 197. 88. Alper CA, Abramson N, Johnston RB Jr, Jandl JH. and Rosen FS: Increased susceptibility to infection associated with abnormalities of complement-mediated functions and of the third component of complement (C3), N Engl J Med 282:349, 1970. 89. Alper CA, Abramson N, Johnston RB Jr, Jandl JH, and Rosen FS: Studies in vivo and in vitro on an abnormality in the metabolism of C3 in a patient with increased susceptibility to infection, J Clin Invest 49:1975, 1970. 90. Ziegler JB, Alper CA, Rosen FS, Lachmann PL and Sherington L: Restoration by purified C3b inactivator of complement-mediated function in vivo in a patient with C3b inactivator deficiency, J Clin Invest 55:668. 1975. 91. Alper CA, Bloch K J, and Rosen FS: Increased susceptibility to infection in a patient with type II essential hypercatabolism of C3, N Engl J Med 288:601, 1973. 92. Sissons JGP, West RJ. Fallows J, Williams DG, Boucher BJ, Amos N, and Peters DK: The complement abnormalities of lipodystrophy, N Engl J Med 294:461, 1976. 93. Fearon DT: Glomerulonephritis, complement and C3NeF (editorial), N Engl J Med 294:495. 1976. 94. Spitzer RE, Vallota EH, Forristal J. Sudora E, Stitzel A, Davis NC, and West CD: Serum C'3 lyric system in patients with glomerulonephritis, Science 164:436, 1969. 95. Sawyer MK, Forman ML, Kuplic LS, and Stiehm ER: Developmental aspects of the human complement system, Biol Neonate 19:148, 1971. 96. Atkinson AW Jr, Curry RH, and Johnston RB Jr: Unpublished observations. 97. Stossel TP, Alper CA. and Rosen FS: Opsonic activity in the newborn: Role of properdin, Pediatrics 52:134, 1973. 98. Feinstein PA, and Kaplan SR: The alternative pathway of complement activation in the neonate, Pediatr Res 9:803, 1975. 99. Winkelstein JA, and Drachman RH: Deficiency of pneumococcal serum opsonizing activity in sickle-celt disease, N Engl J Med 279:459, 1968. 100. Johnston RB Jr, Newman SL, and Struth AG: An abnormality of the alternate pathway of complement activation in sickle cell disease, N Engl J Med 288:803, 1973.

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101. Koethe SM, Casper JT, and Rodey GE: Alternative complement pathway activity in sera from patients with sickle cell disease, Clin Exp Immunol 23:56, 1976. 102. Wilson WA. Hughes GRV, and Lachmann PJ: Deficiency of factor B of the complement system in sickle cell anaemia, Br Med J 1:367, 1976. 103. Hand WL, and King NL: Deficient serum bactericidal activity in sickle cell anemia, .1 Clin Microbiol (in press). 104. Hand WL, and King NL: Serum opsonic activity in sickle cell anemia, Clin Res 24:25A, 1976. 105. Strauss RG, Forristal J, and West CD: The alternative pathway of complement activation in sickle cell anemia, Pediatr Res 9:326, 1975. 106. Johnston RB Jr. Newman SL, and Struth AG: Increased susceptibility to infection in sickle cell disease: Defects of

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opsonization and of splenic function, in Bergsma D, and Good RA, editors: tmmunodeficiency in man and animals, Stamford, 1975, Sinauer Associates, p 322. Minta JO, Jezyk PD, and Lepow IH: Distribution and levels of properdin in human body fluids, Clin lmmunol lmmunopathol 5:84, 1976. Polhill RB Jr, and Johnston RB Jr: Diminished alternative complement pathway activity after splenectomy, Pediatr Res 9:333, 1975. Polhill RB Jr, Pruitt KM, and Johnston RB Jr: Assessment of alternative complement pathway activity in a continuously monitored hemolytic system, Fed Proc 34:983, 1975. Winkelstein JA, and Lambert GH: Pneumococcal serum opsonizing activity in splenectomized children, J PEDIATR 87:430, 1975.