Plasma membrane glycoproteins of cultured rheumatoid synovial fibroblasts

Two-dimensional electrophoresis of synovial tissue, synovial fluid and serum in patients with rheumatoid arthritis and related diseases

Using the technique of two-dimensional (2D) electrophoresis with consecutive silver staining, we investigated samples of serum, synovial fluid and synovial tissue obtained from 19 patients suffering from rheumatoid arthritis (RA) or non-RA arthritis. From these experiments we have drawn the following conclusions. 2D electrophoresis of serum, synovial fluid and synovial tissue extracts taken from patients suffering from joint diseases is a reproducible method. Repeated runs of the same sample reveal an essentially constant protein spot pattern. The time period between surgery and tissue preparation did not influence the number of protein spots when less than 15 h was involved. The protein spot number is always lower in synovial fluid than in either synovial tissue or serum in RA and non-RA patients. The mean value for the number of spots is 68 for the inflamed tissue irrespective of the cause of arthritis (RA and non-RA group taken together) and 47 for the control group. This difference is significant. We were able to definitely identify 7 spots in the tissue extract. We did not find RA-specific protein spots in either serum, synovial fluid or tissue extracts from the synovial membrane. The only significant difference between RA patients and either non-RA or control group patients concerning the protein spot pattern is the increased size of the immunoglobulin spot (mainly IgG) in RA. In addition, we discuss possible reasons for failure of the 2D electrophoresis technique to detect disease-specific protein patterns.

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.

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.

Surface membrane glycoproteins of macrophage-like synovial cells from rheumatoid and control patients

Synovial cells were prepared by enzyme digestion and Percoll gradient centrifugation of rheumatoid arthritis (RA) synovial specimens or by trypsin-rinsing of non-inflammatory cadaver joints. Most (70-80%) of the cells from RA patients were OKIa -positive macrophage-like cells, 10-20% other OKIa -positive cells, and about 10% fibroblastic cells, whereas 90% of the normal synovial cells were OKIa -positive macrophage-like cells and the rest fibroblasts. These adherent synovial cells were compared with fibroblastic synovial cells obtained by sequential passaging of explanted dividing cells. Periodate-[3H]borohydride labelling followed by SDS-gradient gel electrophoresis demonstrated similar sialo-glycoprotein patterns in both the adherent synovial cells and synovial fibroblasts. The molecular weights of the main surface glycoproteins resembled closely those of skin fibroblasts but not those of peripheral blood monocytes. RA samples showed inconsistent heterogeneity. The results indicate either that all synovial cells possess a similar basic structure or that macrophages of peripheral blood origin express fibroblastic contact glycoproteins when settling down into synovium.

Characterization of plasma membranes and rough endoplasmic reticulum of synovial cells cultured from rheumatoid arthritis patients

[35S]methionine-labelled plasma membrane (PM) and rough endoplasmic reticulum (RER) proteins were analysed from synovial cell cultures derived from rheumatoid arthritis (RA) and reference patients. Pure RER was prepared by a modification of CsCl-containing sucrose-cushion method. The PM proteins were resolved into 30-35 bands using sodium dodecyl sulphate-electrophoresis in polyacrylamide gradient gels. The major polypeptides had apparent molecular masses of 170, 140, 110, 60, 40, 33, 23 and 14 kilodaltons. The major RER polypeptides had the apparent molecular masses of 170, 74, 58 and 35 kD. No reproducible differences were demonstrated in the polypeptide patterns or in the specific activities of the PM and ER (endoplasmic reticulum) marker enzymes between cells from RA and reference patients. The results reflect similarities of membrane structures in RA and reference cells, although differences have been reported in their metabolism.