BIOCHEMICAL-CHARACTERIZATION AND MICROSEQUENCING OF A 205-KDA SYNOVIAL PROTEIN STIMULATORY FOR T-CELLS AND REACTIVE WITH RHEUMATOID-FACTOR CONTAINING SERA

Synovial fluid (SF) was found to possess stimulatory capacity for the proliferation of T cell clones derived from patients with rheumatoid a rthritis (RA) when cultured together with IL-2. Using chromatography t echniques and gel electrophoresis, a synovial fluid protein with an ap parent m.w. of 205 kDa (p205) was isolated that demonstrated a bioacti vity analogous to that obtained with native synovial fluid. After elec troelution, p205 dissociated into 70-kDa fragment(s). Upon IEF, it app eared as a single band with an isoelectric point of 6.5, suggesting a noncovalently bound trimer complex. Amino acid sequences of the whole protein and of tryptic peptides were determined by N terminal sequenci ng. The N terminal amino acid sequence of the 70-kDa fragment and of t he tryptic peptides showed no identity to recently described protein s equences. One petide matched, in 11 amino acid residues, with the huma n IgG(1-4) constant heavy chain and rheumatoid factor (RF) binding reg ion. The p205 induced the proliferation of peripheral blood T cells an d long term T cell cultures that had been raised by alternate stimulat ion with IL-2 and p205. In a similar approach, synovial lining cells w ere shown to release a protein with biochemical characteristics simila r to the synovial fluid-derived p205 Western blot analysis revealed th e binding of RF-containing sera to p205, which was diminished by absor ption with an RF reagent. These observations suggest that p205 is expr essed by synovial cells and may be a target for T and B cells in RA.