Pathogenesis of sarcoidosis: An hypothetical model

rogram in Biochemistry,

An hypothetical model for the pathogenesis of sarcoidosis is presented which is compatible with its generalized nature, lack of an apparent etiologic agent and biochemical difference from other granulomas, including marked elevation of angiotensin converting enzyme. Widespread genetic alteration of epithelioid cell precursors by a virus or early precursor mutation is hypothesized to trigger transformation to epithelioid cells and the synthesis of certain proteins which may differ qualitatively from those of non-sarcoid epithelioid cells. At some point in the transformation the epithelioid cells develop an affinity for each other by altered surface properties, resulting in the widespread formation of granulomas.

proven causative agent in sarcoidosis suggests that either the agent is an unusual one which is difficult to detect or that perhaps none is present in the usual sense. Both of these alternatives are considered in the proposed disease mechanism which involves an intrinsic biochemical, genetic, cellular alteration rather than the stimulation of an external non-host antigen or other substance.

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Sarcoidosis is an zed granulomatous disease of unknown cause and varied clinical course which is sometimes associated with aberrant metabolic manifestations, such as hypercalciuria and hyper-prolactinemia (l-3). Angiotensin converting enzyme (ACE) is significantly elevated in the serum in under half the cases of sarcoidosis as compared to normal controls and patients with other common diseases, including the well defined granulomatous disease, tuberculosis (4,5). Virtually all sarcoid granulomatous lymph nodes but not tuberculous lymph nodes (6) or Freund’s adjuvant granulomas in the rat (7) have markedly elevated ACE specit?c activity which generally exceeds that of lung, which is the highest of the major organs (8). The high CE (6) and electron microscopic appearance of active biosynthesis rather than phagocytosis (9) of sarcoid granulomatous lymph nodes suggest that the sarcoid granuloma may, with some degree of specificity, be actively synthesizing ACE, resulting in elevated serum ACE in some patients (6). While less likely than increased biosynthesis, specific uptake of ACE by the sarcoid granuloma and diminished elimination of it has not been ruled out. inactivation studies suggest the possibility that the ACE in the sarcoid granuloma may be abnormal (6). The observation of elevated ACE in sarcoid lymph nodes (4) and the biosynthetically active fine structural appearance of epithelioid cells in sarcoid granulomas (9) suggests the possibility that other biologically active macromolecules may be elaborated by the sarcoid granuloma, perhaps resulting in some cases in metabolic aberrations. kysozyme was elevated in sarcoid lymph nodes (10) and serum lysozyme, which is generally elevated in sarcoidosis (1 l), was significantly correlated with serum ACE, suggesting a linkage between the two enzymes in the disease (10). Based on these observations and 1) the generalized nature of sarcoidosis 2) the absence of a proven etiologic agent despite extensive search and 3) the apparent biochemical difference between the granuloma of sarcoidosis and other granulomas, an hypothetical model for the pathogenesis of sarcoidosis is proposed. The inability in finding a

The cellular even e formation of the epithelioid cells of granulomas are depicted in Figure 1. Hn non-sarcoidosis

cell. The precise mechanism by which this occurs is not specified. It is possible that lymphocytes may be involved in a cooperative manner at some point in the process. The ulus to epithelioid cell formation could be the bi to a precursor cell membrane receptor, bindin lymphocyte membrane receptor and elaboratio lymphocyte of a substance which stimulates epithelioid cell formation, or another mechanism. In sarcoidosis (right) the precursor cell is triggered to transform to an epithelioid c y a genetic alteration of the cell, as by insertion of vir A into the cell in a nonintegrated episome or pla eft) or in a form recombinant with the host chromosome (right), or by a mutation in a chromosomal gen derepression of an hereditarily A (right). This event triggers the passed segment of viral formation of the A, B, C, etc. proteins characteristic of epithelioid cells, plus additional proteins, e.g. V, W (coded for by viral or mutated chromosomal genes) and X, Y, Z (coded for by previously repressed chromosomal genes). The product of the viral or mutated chromosomal gene, e.g., V, might stimulate the transcription of the A, B, C, etc. genes as well as the W, X, Y, Z genes and the con75

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Fig. l-Hypothetical model at the genetic level of the mechanism of epithelioid cell formation in sarcoidosis (right) and non-sarcoidosis (left). The granuloma stimulating substance may be antigenic or non-antigenic and may act directly or indirectly through interaction with other cells

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(e.g.,lymphocytes). Note that the epithelioid cells in non-sarcoidosis and sarcoidosis are not identical although they have common features. See text for details.

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Fig Z-Hypothetical model of localized (non-sarcoidosis) and generalized (sarcoidosis) granuloma formation. GSS, granuloma stimulating substance, which may be antigenic or non-antigenic: X, epithelioid cell precursor; Y, precursor to the epithehoid cell precursor; E. epithelioid cell. In non-sarcoidosis localized granulomas are formed by attraction of epithelioid cell precursors to localized sites of

INTRINSICALLY TRANSFORMED EPITHELIOID CELLS

granuloma stimulating substances where they are transformed epithelioid in sarcoidosis are generalized because . . cells. . Granulomas ^.. genenc alteranon of wtdespread epithelioid cell precursors by virus intrinsic cellular alteration (see Fig. 1) by which they are triggered transform to epithelioid cells. Granulomas are assumed to form due affinity of these cells for each other at some point in the transformation.

76

to of or to to

comitant transformation to a sarcoid epithelioid cell. aintenance or decline of the epithelioid cell might depend on the continued formation of the stimulatory V protein. One of the additional proteins, ACE, may be coded for by a viral or mutated host gene (W) or a previously repressed chromosomal gene (Z). Alternatively, one or more additional proteins may be responsible for a large specific uptake of ACE by the sarcoid epithelioid cell. The additional proteins are biologically active and may account for certain clinical manifestations. The additonal proteins may vary in individual sarcoidosis cases, depen the precise nature of the viral or the site of insertion of the chromosome. The course of t sarcoidosis may depend on the persistance of a stimulatory gene product (e.g., V) by continued biosynthesis or lack of degradation, and the destructive or non-destructive effect of other additional proteins on the tissue in which the granuloma is situated. A model compatible with the generalized nature of on-sarcoidosis is sarcoidosis is shown in Fi depicted as localized to the s precursors are attracted to (directly or indirectly as aforementioned), as indicated in epithelioid cells which are grouped Figure 1, to trans in the granuloma arcoidosis is depicted (Figure 2) as generalized due to widespread genetic alteration of epithelioid cell precursors as noted in Figure 1. The widespread alteration derives from dissemination of a virus as by viremia (middle line of cells) or mutation or derepression in a precursor to the immediate epithelioid cell precursors (right line of cells). The result in both cases is the formation of widespread epithelioid cell gered to transform to epithelioid precursors which are some point in the transformation cells (as in Figure 1). of altered epithelioid cell precursors to epithelioid cells through intermediate stages, the surface properties of the cells alter so that they develop an affinity for each other, resulting in groups of epithelioids cells in granulomas. The other cells of the granuloma are attracted to it, perhaps by one or more of the sarcoidosis epithelioid cell proteins (Figure 1). The epithelioid cell precursor and its precursor are not specified, but may be the monocyte and monoblast ( 12). The defective delayed hypersensitivity, hyperactive humoral antibody synthesis (1) and atypical lymphocyte forms (13) in sarcoidosis may be due to elaboration by epithelioid cells of molecules which influence these functions (e.g., by inhibiting T cell production or function or increasing their destruction, and the production of opposite effects on B cells). Alternatively, altered epithelioid cell precursors may function defectively in delayed hypersensitivity in cooperation with T cells, and particularly well in humoral antibody synthesis in cooperation with B cells (14, 15). The long delayed granulomatous skin reaction to intradermal processed sarcoidosis granulomatous lymph node or spleen (Kveim-Siltzbach test) in patients with sarcoidosis, but generally not in control subjects (16), may have several possible explanations. 1) Transmission of virus from the

veim-Siltzbach antigen, setting up a granulomatous reaction (Figure 1, 2) in sarcoidosis patients who are susceptible to the virus, but not in non-sarcoidosis who are not susceptible. The inactivation of the iltzbach antigen on heating at 100° and the slow development of the lesion are compatible with a slow virus etiology, though an immunologic mechanism is also possible. The familial occurrence of sarcoidosis, suggesting a genetic influence as well as possible environmental interaction in the disease (17-20) is compatible with the possibility of a host susceptibility factor. 2) ensitivity of the sarcoidosis patient to a non-host, presumably viral, antigen which is produced in the sarcoidosis granuloma. 3) Interaction in the sarcoidosis recipient of a particulate (2 1) antigen in the Siltzbach preparation with a factor(s) elaborated by the granulomas of the sarcoidosis subject and perhaps mrther metabolized in the patient, to produce a granuloma in the sarcoidosis recipient, but not in the non-sarcoidosis recipient. Altered T and B lymphocyte function may also play a role in any of the mechanisms.

mechanism for the In view of the p pathogenesis of sarcoidosis and the association of the disease with elevated ACE, it is of interest that elevated 6 been found ’ ACE has serum (22) and 7 of 10 (23) patients with Gaucher’s dk:ase, a genetic disease of the reticuloendothelial system associated the acid hydrolase with a deficiency in the activit e the relationship glucosylceramide+glucosidase. between elevated serum ACE and the two diseases is not clear, there is a possibility of a similarly altered control mechanism for ACE operating at the genetic level in both cases.

el are A number of possible tests implicit in its presentation. may be isolated. Serial passage of unautoclaved, filtered, unirradiated granulomas from sarcoidosis patients in mice has been adduced as evidence for a viral etiology of sarcoidosis (24), although contrary evidence has also been obtained (25). If a virus is isolated, the possibility of difference in susceptibility to infection of cells from sarcoidosis subjects and their relatives as compared to control subjects could be tested. Early epithelioid cell precursors from sarcoidosis patients and close relatives could be placed in long term culture to determine whether epithelioid cells with the biochemical characteristics of sarcoidosis granulomas would result, presumably by a mechanism other than incorporation of external virus (Figure 1,2). Various granulomas may be investigated to determine whether they differ biochemically from the sarcoidosis granuloma. Additional biologically active molecules may be sought in sarcoidosis granulomas which may elucidate certain clinical findings in sarcoidosis. Isolation of non-host protein from sarcoidosis granuloma would indicate the likelihood of an infective etiology. An affinity of epithelioid cells of sarcoidosis granulomas for each other may be dem77

11.

onstrated. This affWy may or may not differ from that of non-sarcoidosis epithelioid cells.

,1074,1973

This work was supported in part by

14. 15.

1. 2.

3. 4. 5. 6.

7.

16.

of Medicine, Beeson PB, James DG. Sarcoid McDermott W, eds, Saunders WB Philadelphia, 1975 14th ed ~164 Mitchell DN. Scaddine. JG. Sarcdidosis. Amer Rev Resn Dk 774.1974 -’ Turkington RW, Macindoe JH. Hyperprolactinemia in Sarcoidosis.

17.

Cushman D, Cheung HS. Concentrations of angiotensin-converting enzyme in tissues of the rat. Biochim Biophys Acta. 250, 261,

9.

James EMV, Jones Williams W. Fine structure and histochemistry of epithelioid cells in sarcoidosis. Thorax. 29, 115, 1974 Silverstein E. Friedland J. Ackerman T. Elevated lvsozvme activitv in non-necrotizing granulomatous lymph nodes in-sarcbidosis. Clin Res. 23,60OA, 1975

British Thoracic and Tuberculosis Association. Familial associations in sarcoidosis. Tubercle. 5 19. Headings VE. Young RC Jr, Hackney RL Jr, Weston D. Familial sarcoidosis with multiple occurrences in ten families. Seventh International Conference on Sarcoidosis and other granulomatous disorders, New York, October 6-10, 1975, no. 39 20. Sharma OP. Familial sarcoidosis: possible genetic influences. ibid., no. 40 21. Ripe E, Izumi T, Kallner A, Ljungqvist A, Nilsson BS, Unge G. On the active principle in the Kveim suspension. Stand J Resp 22.

1971 -_ _

10.

Macrophage physiology. Fed Proc. Biberfeld P, Hedfors E. Atypical blood lymph0 morphology, cytochemistry and membrane properties. Stand J Immunol. 3,615, 1974 Unanue ER, Calderon J. Evaluation of the role of macropha immune induction. Fed Proc. crophage-lymphocyte Rosenthal AS, Lipsky PE, Sh interaction and antigen recognition. Fed Proc. 34, 1743, 1975 James DG, Neville E, Walker A. Immunology of sarcoidosis. Amer J Med. 59,388, 1975 occurrence of sarcoidosis. Stand J Resp Dis

18.

Lieberman J. Elevation of serum angiotensin-converting-enzyme (ACE) level in sarcoidosis. Am J Med. 59.365, 1975 Silverstein E, Friedland J, Lyons H, Kitt M. Serum angiotensin converting enzyme in sarcoidosis. Clin Res. 23,352A, 1975 Silverstein E, Friedland J, Lyons H, Gourin A. Elevated angiotensin converting enzvme activity in non-necrotizing granulomatous lvmnh nodes in sarcoidosis. Clin Res. 23, 352A, 1975; Proc NatAcad Sci USA, 73, 1976 in press Silverstein E, Friedland J. Lack of elevation of angiotensin converting enzyme in Freund’s adjuvant granuloma in the rat. Fed

8.

Pascual RS, Gee JBL, Finch SC. Usefulness of serum lysozyme measurement in diagnosis and evaluation of sarcoidosis. N Engl

;::

25.

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Lieberman J. The specificity and nature of serum angiotensinconverting-enzyme (ACE) elevations in sarcoidosis. Seventh International Conference on Sarcoidosis and Other Granulomatous Disorders, New York, October 6-10, 1975, no. 48 Silverstein E, Friedland U. Clin Res 2 Mitchell DN, Rees RJW. The nature and physical characteristics of a transmissible agent from human sarcoid tissue. Seventh International Conference on Sarcoidosis and Other Granulomatous Disorders. New York. October 6-10. 1975. no. 26 Iwai K, Takahashi S. Transmissibility of sarcoid-specific granulomas in the footpads of mice. ibid., no. 27