Studies of serum immunoglobulin binding to synovial fibroblast cell cultures from patients with rheumatoid arthritis

Autoantibodies from rheumatoid arthritis patients recognize antigens on the synoviocyte surface

We have found autoantibodies in the sera from rheumatoid arthritis (RA) patients which recognize two cell surface antigens of approximately 70 kDa and 28 kDa from synoviocyte extracts as detected by immunoprecipitation analysis. These polypeptides were immunoprecipitated from extracts containing mainly macrophage-like synoviocytes (type A) but not from extracts of homogeneous fibroblast-like synoviocytes (type B). These autoantigens are not selectively expressed by RA synoviocytes, since both RA and non-rheumatoid synovia were reactive for RA sera. From the panel of different RA sera tested, 64% immunoprecipitated the 70 kDa band, and 27% recognized the 28 kDa polypeptide. These differences in the specificity of the sera seemed to be related to the clinical state of the donor. The sera from patients suffering from other autoimmune diseases such as autoimmune thyroiditis and systemic lupus erythematosus (SLE) do not appear to be reactive for these specificities, but sera from patients with Sjögren's syndrome, psoriatic arthritis, and Crohn's disease showed a weak cross-reactivity with the 70 kDa polypeptide. This autoreactivity against synovial cells in RA supports the idea that these cells participate in the initial immune response of the disease.

Etiology of rheumatoid arthritis

Definite genetic associations with immunological cooperative HLA-D(R) antigens have been demonstrated for rheumatoid arthritis (RA). Microbial etiology has not been proven, but some hope for the supporters of this view is still given by small viruses, plasmids of enteric bacteria or perhaps oncogen-like DNA-sequences. Yet, electrophoretical analysis of membrane proteins or surface glycoproteins of RA synovial cells does not show any differences compared to reference cells. Autoimmunity to several tissue elements has been demonstrated, but most of it is of secondary nature. Antigenicities of type II and III collagens are probably only contributory factors for HLA-DR4 positive individuals. Proteoglycans or minor cartilage collagens have not been extensively studied, so far. Endocrine, dietary or psychological influences might be triggering events for otherwise 'preloaded' individuals.

Antibodies to cultured rat heart cells in sera of patients with rheumatoid arthritis

Since heart lesions occur in many patients with rheumatoid arthritis (RA), sera from these patients were tested with an indirect fluorescent technique for antibodies reactive with rat heart cell cultures. Of 27 sera 22 had reactivity with non-muscle (nM) cells and 3 reacted with cultured beating muscle cells (M). Positive sera reactive with nM cells exerted complement-dependent cell cytotoxicity towards M cells. The nM antibodies were found to belong predominantly to the IgG class. They displayed no cross-reactivity with bovine collagen, human and bovine serum proteins, or human and sheep red blood cells. The relationship of these antibodies to the pathogenesis of RA heart lesions remains to be determined.

Antigenicity of proteins from cultured synovial fibroblasts

We were able to characterize about 25 antigenic proteins of cultured synovial fibroblasts with apparent molecular weights of 15-230 kd by SDS-electrophoresis and immunoblotting using guinea pig antiserum. Some of these proteins were bovine-serum-derived, adsorbed onto fibroblasts from culture medium. Both rheumatoid and normal sera contained natural antibodies reacting with synovial fibroblast as well as bovine serum antigens when studied with immunoblotting. The amounts of antibodies were quantitated with enzyme immunoassay, measuring IgG and IgA class antibodies against plasma membrane preparations of rheumatoid and normal synovial fibroblasts. No rheumatoid arthritis-related changes were detected in synovial fibroblast protein antigens or antibodies against them in rheumatoid patient specimens.

Plasma membrane glycoproteins of cultured rheumatoid synovial fibroblasts

Fibroblast cultures were started from synovial tissue samples of 12 rheumatoid arthritic, 9 non-rheumatoid synovitic and 6 control patients. External galactose units of plasma membrane glycoproteins of confluent cells were labelled using the galactose oxidase-tritiated borohydride method. These surface-labelled cells were analyzed for possible differences in their glycoproteins by electrophoresis in SDS-containing polyacrylamide gradient gels. Total cell lysates were separated into 50-60 polypeptide bands. Fluorography of the gels revealed about 20 labelled plasma membrane glycoproteins. Some strain-specific differences were detected between the samples in all the groups, but no correlation with rheumatoid arthritis could be demonstrated.