Evidence for the presence of receptors for c3 and IgG Fc on human synovial cells.код для вставкиСкачать
1 ARTHRITIS & RHEUMATISM OFFICIAL J O U R N A L OF T H E AMERICAN RHEUMATISM ASSOCIATION SECTION OF T H E A R T H R I T I S F O U N D A T I O N EVIDENCE FOR THE PRESENCE OF RECEPTORS FOR C3 AND IgG Fc ON HUMAN SYNOVIAL CELLS ARGYRIOS N. THEOFILOPOULOS, DENNIS A. CARSON, MEHDI TAVASSOLI, SUSAN F. SLOVIN, WENDELL C. SPEERS, FRED B. JENSEN,and JOHN H. VAUGHAN The presence of receptors for IgC Fc and fragments of C3 on primary cultures and cryostat sections of normal and rheumatoid synovial tissues was assessed. Significant proportions of large rounded cells with asteroid projections found in such cultures had receptors for both IgC Fc and fragments of C3. Moreover, Cram negative bacteria that had fixed complement, but not EAC, bound in a linear fashion on the superficial layers of synovial cryostat sections. On the basis of morphologic and histochemical criteria, the cultured cells bearing these receptors were tentatively determined to represent a subset of synovial lining cells. The possible role of such receptors on synovial lining cells in the pathogenesis of rheumatoid arthritis is discussed. From the Departments of Immunopathology, Clinical Immunology and Cellular and Developmental Immunology, Scripps Clinic and Research Foundation, La Jolla, California. Supported in part by NIH grants AM-21175, AM-25443, AM-255 10, and AI-07007, and DOE contract DE-AS03-79EV00899. Argyrios N. Theofilopoulos, MD: Associate Member, Department of Immunopathology (recipient of Research Career Development Award CA-00303); Dennis A. Carson, MD: Assistant Member 11, Department of Clinical Research Mehdi Tavassoli, MD: Assistant Member 11, Department of Clinical Research; Susan F. Slovin, PhD: Research Fellow, Department of Clinical Research; Wendell C. Speers, MD: Research Fellow, Department of Immunopathology; Fred C. Jensen, DVM: Associate Member, Department of Cellular and Developmental Immunology; John H. Vaughan, MD: Member, Department of Clinical Research. Address reprints to Argyrios N. Theofilopoulos, MD, Department of Immunopathology, Scripps Clinic Research Foundation, 10666 North Torrey Pines Road, La Jolla, California 92037. Submitted for publication July 10, 1979; accepted in revised form August 27, 1979. Arthritis and Rheumatism, Vol. 23, No. 1 (January 1980) The light and electron microscopic appearance of human normal, osteoarthritic, and rheumatoid synovia has been described by various authors (14). In general, these authors have described three types of synovial lining cells which have been classified as types A, B, and C. The type A cell was described as a large phagocytic cell, the type B as a large nonphagocytic cell, and the type C as a small phagocytic cell which may represent a monocyte-derived macrophage rather than a true synovial lining cell. Although there are several studies on the surface markers of the human synovial infiltrating cells as well as of the mononuclear cells in synovial fluids of rheumatoid patients (5-9), there is little information about the types of surface receptors on human synovial lining cells. In view of the role of cell surface receptors for IgG Fc and C3 on cell-cell interactions and cell activation or inactivation (lo), we decided to examine the presence of such surface receptors on cells derived from primary cultures of human synovial membranes. Our results indicate that the majority of large cells with finger-like projections in such cultures do carry receptors for fragments of C3 and for IgG Fc and that based on histochemica1 and other criteria, these cells appear to be synovial lining cells. The possible role of such receptors in the pathogenesis of rheumatoid arthritis is presented. MATERIALS AND METHODS Synovial tissues. Synovial tissues from 3 patients with rheumatoid arthritis, 2 patients with osteoarthritis, and 2 normal persons with traumatic arthritis provided the source for THEOFILOPOULOS ET AL 2 Figure 1. Monolayers of cultured synovial cells stained with Wright-Giemsa. Elongated and rounded cells with fine projections are noted (A, x 250; B, x 400). synovial cells. Minced synovial tissues were suspended in 50 ml of minimum essential medium (Eagle’s MEM) containing 1,500 units of clostridial collagenase (Sigma) and 0.25% trypsin and were incubated under constant stirring at 37OC for 1 hour. Cells isolated from the digested synovium were washed 3 times with the medium supplemented with 10% fetal bovine serum to inhibit digestion, then washed twice, resuspended to 1 X lo6 cells/ml and distributed into 60 mm Petri dishes. In certain dishes sterile cover slips were added at the start of the culture. Cell cultures were examined daily under the phase inverted microscope. Within 6-7 days the cells became confluent and at that time they were harvested and used in the experiments reported in the following section. Frozen tissue sections of 6-8p thickness from normal and rheumatoid synovia were obtained by use of a microtome, mounted on slides, and stored at -70°C. Cell surface receptor identification. Cultured cells were examined for various receptors either as monolayers on coverslips or as suspension after nonattached cells were washed out and carefully scraped off. Coverslips were washed 3 times with medium, mounted on slides, and overlaid with either a suspension of sheep red blood cells (SRBC) sensitized with IgM rabbit hemolysin and mouse complement (EAC) or with red blood cells sensitized with IgG rabbit anti-ox red blood cell antibody (EA). B lO.D,/old mouse serum was used as a source of complement to form EAC. These intermediates are immune adherence negative and therefore they detect primarily C3d receptors (1 1,12). Methods of preparation of those reagents and of the IgG ox cells have been described elsewhere (1 1-13). After incubation in a humidified box, the coverslips were washed 3 times with large volumes of medium to remove nonattached red cells and mounted on slides under glycerogel. The cells were examined under a phase contrast microscope and the percentage of rosette forming cells was recorded. Controls included cells incubated with nonsensitized SRBC or ox red blood cells. Cultured synovial cells in suspension were examined for rosetting with neuraminidasetreated SRBC and for the presence of surface bound Ig by use of a polyvalent fluorescein isothiocyanate (FITC) conjugated rabbit antiserum to human immunoglobulins (Cappel Laboratories) as described (14). Synovial cells in suspensions were also first reacted with FITC anti-human Ig antibody at 4°C for 30 minutes and after 3 washes they were incubated with EAC or EA to determine if rosette forming cells had Ig on their surface. On occasion the presence of C3 receptors on cultured synovial cells in suspension or monolayers was determined using FITC conjugated Salmonella typhii which had reacted with fresh human serum as a complement source (15). The human serum used in these experiments as a complement source had been prescreened for Salmonella febrile agglutinins, group D, by bentonite flocculation. Only a serum with undetectable agglutinins was used. Soluble human C3b and F(ab’)* fragments of an FITC-rabbit anti-human C3 antibody were prepared as described and binding of soluble C3b to cultured synovial cells in suspension was examined by immunofluorescence (14). RECEPTORS FOR C3 AND IgG Fc 3 Figure 2. IgG Fc (A) and C3 receptors (B, C) on cultured synovial cells (A, Frozen synovial tissue section studies. Frozen synovial tissue sections, 6 to 8p thick, on glass slides, were overlaid with fluorescein (F1TC)-conjugated Salmonella typhii that had fixed human complement (5 X lo9 particles/ml in tissue culture media with 5% bovine serum albumin to reduce nonspecific binding). After incubation at room temperature for 20 minutes, the slides were dipped vigorously in phosphate-buffered saline to wash free nonspecifically bound bacteria, and the tissue was then examined as a buffered glycerol wet mount under phase and fluorescence light microscopy. Control preparations were similarly incubated with nonopsonized bacteria. Cytochemistry and histochemistry. Cells grown on coverslips were used for cytochemical studies. They were fixed before or after rosetting with EAC using formalacetone (for acid phosphatase studies, methanolacetone was used). For histochemistry, unfixed cryostat sections of the synovial tissues were used. They were stained with Wright-Giemsa, Sudan Black B, peroxidase, periodic acid-Schiff (PAS), alkaline phosphatase, and pyronine. Acid phosphatase staining was carried out according to a modified method of Barka and Anderson by use of naphthol AS-BI phosphate and hexagotized pararosanilin (16). Tartrate inhibition of acid phosphatase was carried out by adding 0.02M liter (+) tartrate to the staining solution. Esterase reactions were carried out according to X 630; B, X 400; C, x 630). the method of Li et a1 (17) with a naphthyl butyrate (for nonspecific esterase, NSE) and naphthol AS D-chloracetate (chloracetate esterase, CAE) as substrates and freshly made hexaxotized new fuschin or pararoseaniline, respectively, as couplers. Staining for acid mucopolysaccharides was done using 1% alcian blue 86 times in 3% acetic acid (18). Electron microscopic studies. Synovial cells on plastic substratum were rosetted with EAC as described previously. Modified Karnovsky’s fixative was used initially, followed by 2% O,O, in 0.125M cacodylate buffer after fixation, staining with saturaged thiocarbohydrazide, and 2% 0,04 fixation, again. Staining with 4% uranyl acetate was performed after partial dehydration to 30% alcohol. After complete dehydration the monolayer was embedded in Epon. Perpendicular sections were mounted on coated grids and then stained with 2% uranyl acetate and 1% lead citrate. RESULTS Morphology of cultures. In the primary cultures and at the sixth to seventh day, the synovial cells were of three types: rounded large cells with some asteroid projections, spindle-like cells, and a variable percent of Figure 3. Cultured synovial cells with fluorescinated attached Gram negative bacteria that had fixed complement (A, 400. B. x 630). X THEOFILOPOULOS ET AL 4 Figure 4. Electron micrographs of cultured synovial cells with attached EAC. fibroblast-like cells (Figure lA, B). The rounded cells with projections comprised about 40-50% of the total population as estimated by phase microscopy. Occasionally, these rounded cells clustered into groups but most often they were single or in pairs. There were no apparent morphologic differences between the synovial cell cultures derived from normal, osteoarthritic, or rheumatoid individuals. However, rheumatoid synovial cultures appear to have a higher proliferative capacity and exhibit higher cellularity. Subcultured synovial cells at the fifteenth subpassage appear elongated with many projections, an appearance similar to that described by Smith (19). Cell surface receptors. Monolayers of rheumatoid, osteoarthritic, and normal synovial cells exposed to EAC or EA showed almost no attachment (only 2-5% rosetting cells) to spindle-like cells or fibroblasts. In contrast, over 85% of the rounded cells with asteroid projections formed rosettes with both types of the sensitized cells (Figure 2A, B, C) as well as with Gram negative bacteria that had fixed complement (Figure 3A, B). Interiorized EA or EAC were se'en very frequently. The percentage of synovial celis in suspension obtained from similar monolayer cultures forming rosettes with EAC and EA was similar (50-60%) to the percentage of rounded cells seen in monolayers. There was no significant difference in the percentage of cells expressing C3 and IgG Fc receptors among synovial cells derived from normal controls, osteoarthritic or rheumatoid patients. No cells were found to form rosettes with control nonsensitized SRBC or ox red blood cells. Approximately 2-6% of detached synovial cells obtained from 6 to 7 day monolayers were found to bear surface Ig. However, these Ig positive cells did not form rosettes with EAC or EA, a finding which suggested that they were B cells in an advanced maturational stage. When synovial cells in suspension were incubated with soluble isolated human C3b or inulin-activated human serum, 35-45% of cells in all cultures studied were found to be surface positive when stained with FITC anti-human C3 antibody. Control cells incubated with medium, instead of C3b, were negative when reacted with the above antiserum. Electron microscopic studies. By transmission electron microscopy the rosetted synoviocytes resembled type A cells of human synovium and the macrophage-like cells of human fetal synovium and rabbit synovium (20-22). The most characteristic feature was the numerous delicate filopodia that extended to contact and finally engulf the erythrocytes (Figure 4A, B). Points of actual contact between the erythrocyte and synoviocyte membranes were relatively small and infrequent until the red cell had become completely internalized. A second feature was the abundance of lucent vacuoles, occasionally more than a micron in diameter, immediately beneath the plasma membrane, especially in areas with numerous filopodia. A third common feature was the phagocytic vacuoles; these were occasionally very large and often contained obvious partially degraded cellular debris. The nuclei of the rosetted cells were often deeply indented, but other ultrastructural features were not particularly characteristic. Many rosetted and fibroblast-like nonrosetted cells contained numerous lipid inclusions approximately 1p in diameter. Most of the rosetted cells had a generally spherical configuration; however, two very elongated cells with RECEPTORS FOR C3 AND IgG Fc 5 Table 1. IgG Fc and C3 receptors and histochemical characteristics of synovial cells Sections (superficial layers) Rounded cells (cultured monolayers) (40-50%) EA EAC C-fixing Gram neg bacteria Acid phosphatase Neg Neg +++ +++ Neg + + Neg Neg Neg Neg +++ +++ +++ +++ Neg Neg Neg Neg Neg Neg Neg Alkaline Nonspecific phosphatase esterase numerous attached and engulfed red cells were seen. In other respects these cells resembled the spherical cells. This suggests that some of the elongated “fibroblastlike” cells in the cultures were in fact derived from the rounded cells. Cytochemistry and histochemistry. These studies were carried out to further characterize the IgG Fc and C3 receptor-bearing cells. The results are summarized in Table 1. The EAC and EA rosetting normal and rheumatoid cultured cells were equally strongly stained for acid phosphatase (Figure 5). The upper layers of synovial tissue cryostat sections were also stained strongly for acid phosphatase (Figure 6A,B,C) but the intensity of reaction was noticeably higher in synovial sections from rheumatoid arthritis patients as compared to normal controls. The acid phosphatase activity was almost totally inhibited by L-tartrate. Although the covering layer of the synovial tissue showed some positive reaction for nonspecific esterase, the cultured cells were completely negative. Similarly, some pyroninophilia was noted in tissue cells, whereas this was absent in cultured cells. However, the upper layers of the tissue sections as well as the cultured cells were negative when stained with peroxidase, chloracetate-reacting esterase, PAS, alkaline phosphatase, Sudan black B, and alcian blue. When cryostate synovial sections from normal and rheumatoid patients were incubated with FITCconjugated Salmonella typhii that had fixed human complement and were then examined under the fluorescent microscope, attachment of the bacteria along the upper layer of the section in a discrete linear pattern was observed (Figure 7A,B). No such attachment was seen in sections incubated with Salmonella typhii without fixed complement or with EAC. DISCUSSION In this report we describe the presence of IgG Fc and C3 receptors on the surface of a portion of cells cul- Pyroninophilia Sudan black B Peroxidase PAS Alcian blue tured from normal and rheumatoid synovia. The receptor-bearing cultured cells had characteristics similar to the type A lining cells as indicated by cytochemical and electron microscopic studies. Extensive studies have been conducted by others on the surface markers characteristic of cells infiltrating rheumatoid synovia and of mononuclear cells in synovial fluids. These studies have indicated the presence of monocyte-derived macrophages, lymphoblasts, and lining cells in synovial fluids and the predominance of T Figure 5. A cultured synovial cell, EAC-rosetted and stained for acid phosphatase. The nucleus (N)is identified. Perinuclear area is heavily stained with acid phosphatase containing granules (Cyt) indicating the presence of abundant lysosomes. Two EAC rosettes are identified intracellularly (arrows) and the cytoplasm of the synovial cell in these areas is particularly rich in lysosomal acid phosphatase ( X 1500). THEOFILOPOULOS ET AL 6 Figure 6. Cryostat section of a normal (A) and a rheumatoid synovium (B and C) stained for acid phosphatase. Note the intense staining at the lining areas. cells in the lymphocytic infiltrates of synovial tissues in rheumatoid arthritis (5-9). Several studies have been focused on the light and electron microscopic appearance of synovial cells ( 1 4 ) and in one study the authors examined the presence of IgG Fc and C3 receptors on cultures of rabbit synovial tissues (21). These authors found that in rabbit synovial explants about 10% of the cells were round and formed rosettes with IgG and C3 markers, whereas the remaining cells were stellate and had no receptors for IgG and C3. The results obtained with rabbit synovial cells are similar to our results with human synovial cells, the only difference being that the proportion of rounded cells bearing these receptors was much higher in human synovial cultures than the reported percentages in rabbit synovial cultures. Our electron microscopic studies have indicated the resemblance of the cultured rosetting synoviocytes with type A cells of human synovium (2) and the macrophage-like cells of human fetal synovium (20) and rabbit synovium (21). Furthermore, the mesothelial nature of the rounded cells bearing the IgG Fc and C3 re- ceptors was demonstrated using cytochemical procedures. Thus, these cells with Wright-Giemsa staining had mesothelial appearance and were positively stained for acid phosphatase, indicating the presence of abundant lysosomes and thereby establishing their macrophage-like nature. However, these cultured cells were negative for peroxidase, alkaline phosphatase, esterases, and PAS, arguing against their granulocytic, monocytic, lymphocytic, or endothelial origin. Additionally, these cells were not noticeably pyroninophilic nor sudanophdic thus making it unlikely that they were RNA enriched cells, plasma cells, or fat cells. On the other hand, the rosetting cultured cells appeared to be identical to some of the lining cells since, like the former cells, the lining cells in synovial cryostat sections were also found to be strongly positive for acid phosphatase and Gram negative bacteria with fixed complement attached to the lining areas in a discrete linear pattern. The stronger intensity of staining for acid phosphatase observed with rheumatoid synovial tissues over that with normal synovium can be attributed to the uptake of rheumatoid fac- Figure 7. Cryostat section of a normal synovium with attachment on the lining areas of fluorescinated Gram negative bacteria that had fixed complement as viewed by fluorescence (A) and phase (B) microscopy. RECEPTORS FOR C3 AND IgG Fc tors and immune complexes in vivo which might have induced the enzyme. The almost total inhibition of the acid phosphatase activity by L-tartrate further distinguishes these cells from such bone-associated macrophages as osteoclasts in which the acid phosphatase is tartrate-resistant (23). Also, the positive staining with nonspecific esterase suggests the presence of some monocyte-macrophages (possibly type C cells) in the superficial layers of synovial tissues. It should be noted that in contrast to the linear attachment of Gram negative bacteria that had fixed complement on the superficial layers of synovial cryostat sections, no attachment of EAC was observed. This result suggests that either the binding of complementfixing bacteria was not mediated via true C3 receptors or that the spatial arrangement and density of the C3 fragments on the bacteria were more conducive to their interaction with cellular C3 receptors than that on EAC. Furthermore, since Gram negative bacteria activate the alternative complement pathway whereas IgM antibody-sensitized sheep red blood cells activate the classic complement pathway, the former indicator particles may carry, apart from the C3 fragments, additional complement components not present on EAC. These components may stabilize the C3 fragments (24) or play a role in the interaction of bacteria with synovial lining cells. It is also of importance to note that Traycoff et a1 (8) found that in contrast to a large percentage (> 80%) of sudanophilic cells that were considered to represent monocytes and monocyte-derived macrophages, a very small proportion (3%) of cells considered to be true lining cells derived from collagenase digested fresh human synovial membranes did form rosettes with EAC. However, as stated previously in our study with primary cultures of synovial cells, the EAC rosetting cells were not sudanophilic, thus making it unlikely that they were infiltrating macrophages similar to those described by Traycoff et al (8). Possibly, in our study we observed high frequency of EAC-rosette forming cells either because of an expansion of the complement-receptor bearing cell population during in vitro culturing or because we used EAC and Gram negative bacteria heavily coated with complement. It is known that EAC rosetting is linearly related to the amount of complement fixed on the indicator particles (10). At any rate, further work is needed to determine with certainty if indeed synovial lining cells have in situ IgG Fc and IC receptors. The presence of IgG Fc and C3 receptors in synovial lining cells would certainly have much impor- 7 tance in mediating phagocytosis of both complement fixing and noncomplement fixing complexes. It is known that synovial tissues of rheumatoid patients are abundant in Ig and complement deposits (25,26) and that synovial fluids contain aggregates of Ig and complement, rheumatoid factor-gamma globulin complexes capable of fixing C lq, nuclear antigen-antibody complexes, low complement levels, and high levels of breakdown products ( C ~ CC3d) , of the third complement component (27-29). Phagocytosis of particulate immune complexes has been shown to be mediated by IgG Fc receptors, and complement promotes attachment of immune complexes to cells (30, 31). Moreover, recent studies have shown phagocytosis of soluble immune complexes via C3 receptors without the necessity of Fc receptor participation (32). It cannot be concluded from the present study whether the C3 receptors observed on synovial cells are CR1 (C3b, immune adherence receptors), CR2 (C3d receptors), or CR3 (C3bi receptors) since the binding of soluble C3b described can be mediated via the fixation of the C3d portion of the molecule on the C3d receptors (10,33,34). Inhibition studies with isolated fragments of C3 and various types of EAC are needed to answer this question. At any rate, immune complexes formed in the synovial fluids of rheumatoid patients may bind to Fc and C3 receptors of lining cells, thereby being phagocytosed. The result would be release of granules and lysosomal enzymes. Similar release of lysosomal enzymes may occur after interaction of macrophage-like cells with soluble C3 breakdown products (35). Such enzymes in turn would cause the cleavage of fluid phase C3, resulting in the production of C3b which could then bind to the lining cells and stimulate release of enzymes, thus leading to chronic inflammation. This concept is similar to that advanced by Schorlemmer et a1 (35) for explaining the role in inflammatory processes of the activation of macrophages by soluble C3b. Additionally, in view of the recent findings by Alspaugh et a1 (36) of a high frequency in rheumatoid arthritis of antibodies to Epstein-Barr virus (EBV) induced nuclear antigens and the findings of Jondal and coworkers (37) indicating that the receptors for C3 are closely associated or identical to receptors for EBV, synovial lining cells with C3 receptors may be a susceptible target for EBV infection. Experiments in our laboratory are aiming at further determining the true nature of the Fc and C3 receptor bearing cells, in examining the biologic effects of immune complex interaction with cultured synovial cells, and in assessing the presence of THEOFILOPOULOS ET AL 8 EBV antigens on synovial lining cells from rheumatoid patients and the susceptibility of these cells to EBV infection. ACKNOWLEDGMENTS The excellent editorial and secretarial assistance of Ms Phyllis Minick and Ms Lorene Masewicz is gratefully acknowledged. REFERENCES 1. Norton WL, Ziff, M: Electron microscopic observations on the rheumatoid synovial membrane. Arthritis Rheum 9589, 1966 2. Kinsella TD, Baum J, Ziff M: Studies of isolated synovial lining cells of rheumatoid and nonrheumatoid synovial membranes. Arthritis Rheum 13:734, 1970 3. Williamson N, James K, Ling NR, Holt LP: Synovial cells: a study of the morphology and examination of protein synthesis of synovial cells. Ann Rheum Dis 25534, 1966 4. 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Bartfeld H: Rheumatoid arthritic and non-rheumatoid synovium in cell culture. Morphological observations, acridine-orange and fluorescent fraction I1 studies. Ann Rheum Dis 24:3 1, 1965 23. Wergedal JE: Characterization of bone acid phosphatase activity. Proc SOCExp Biol Med 134:244, 1970 24. Theofilopoulos AN, Perrin LH: Binding of components of the properdin system on human lymphoblastoid cells and B type peripheral lymphocytes. J Exp Med 143:271, 1976 25. Kinsella TD, Baum J, Ziff M: Immunofluorescent demonstration of an IgG complex in synovial lining cells of rheumatoid synovial membrane. Clin Exp Immunol 4:265, 1969 26. Rodman WS, Williams RC, Bilka PL, Miiller-Eberhard HJ: Immunofluorescent localization of the third component of complement in synovial tissue from patients with rheumatoid arthritis. J Lab Clin Med 69:141, 1967 27. Winchester RJ, Kunkel HG, Agnello V: Occurrence of yglobulin complexes in serum and joint fluid of rheumatoid arthritis patients: use of monoclonal rheumatoid factors as reagents for their demonstration. J Exp Med 134:286, 1971 28. Agnello V, Winchester RJ, Kunkel HG: Precipitin reactions of the C l q component of complement with aggregated y-globulin and immune complexes in gel diffusion. Immunology 19:909, 1970 29. Nydegger JE, Zubler RH, Gabay R, Joliat G, Karagevrekis CH, Lambert PH, Miescher PA: Circulating complement breakdown products in patients with rheumatoid 9 RECEPTORS FOR C3 AND IgG Fc 30. 31. 32. 33. 34. arthritis. Correlation between plasma C3d, circulating immune complexes and clinical activity. J Clin Invest 592362, 1977 Nussenzweig V: Receptors for immune complexes on lymphocytes. Adv Immunol 19:217, 1974 Ehlenberger AG, Nussenzweig V: The role of membrane receptors for C3b and C3d in phagocytosis. J Exp Med 145:357, 1977 van Snick JL, Masson PL: The effect of complement on the ingestion of soluble antigen-antibody complexes and IgM aggregates by mouse peritoneal macrophages. J Exp Med 148:903, 1978 Ross GD, Polley MJ: Specificity of human lymphocyte complement receptors. J Exp Med 141:1163, 1975 Ross GD, Rabellino EM: Identification of a neutrophil and monocyte complement receptor (CR3) that is distinct from lymphocyte C R l and CR2 and specific for a site contained within C3bi. Fed Proc 38:1467, 1979 35. Schorlemmer HU, Davies P, Allison AC: Ability of activated complement components to induce lysosomal enzyme release from macrophages. Nature 261:48, 1976 36. Alspaugh MA, Jensen FC, Rabin H, Tan EM: Lymphocytes transformed by Epstein-Barr virus: induction of nuclear antigen reactive with antibody in rheumatoid arthritis. J Exp Med 147:1018, 1978 37. Jondal M, Klein G, Oldstone MBA, Bokisch VA, Yefenof E: Surface markers on human B and T lymphocytes. VIII. Association between complement and Epstein-Barr virus receptors on human lymphoid cells. Scand J Immunol 5:401, 1976 ARA National Scientific Meeting May 28-31, Hyatt Regency Hotel, Atlanta, Georgia Information o n registration, hotel reservations, and the various sessions t o be held during the week of the National Scientific Meetings of the American Rheumatism Association will be available in March and will be sent t o all ARA members. Non-members may write t o the ARA Assistant Executive Secretary, Angel Fortenberry, for information. Specific details on times, topics, and speakers for the ARA Workshops and Postgraduate Clinical Seminars will be announced in future issues of Arthritis and Rheumatism.