Immortalized B-lymphocytes from rheumatoid synovial tissue show specificity for bacterial HSP 60

Several studies indicate a pathogenetic role of T-lymphocytes with specificity for heat shock proteins (HSP) in rheumatoid arthritis (RA). Surprisingly, there are no experimental data for B-lymphocytes with specificity for HSP. To investigate whether B-lymphocytes from rheumatoid synovial tissue show a specificity for HSP 60 we immortalized synovial tissue B-lymphocytes by the electrofusion technique and tested the specificity of the B-cell clones for HSP 60 by ELISA. Tissue samples from four patients with classic, active RA were used in this study. The isolated cells were electrofused in strongly hypo-osmolar medium with cells either of the mouse strain X63-Ag8-653 (Ag8) or the heteromyeloma strain HAB-1. Clones positive for IgG, the IgG fraction of the supernatant of the isolated synovial cells and the IgG of the serum of the patients were tested in an ELISA for reactivity to the recombinant HSP 60 or Yersinia enterocolitica, which shows great homology with mycobacterial HSP 65 and human HSP 60. The expression of this HSP 60 was studied in normal and rheumatoid synovial tissue using a polyclonal rabbit serum against HSP 60 from Y. enterocolitica (Ye HSP 60). In this way we investigate differences in the expression of HSP 60 and compared the pattern of this HSP60 with the pattern of mycobacterial HSP65 and human HSP 60 described by others. In three of four patients 10 IgG secreting B-cell clones showing a specificity for HSP 60 were detected. IgG specific for HSP 60 was also detected in the supernatant of the isolated synovial cells before fusion and in the serum of these patients. HSP 60 was demonstrated immunohistochemically within the rheumatoid synovial tissue and showed stronger expression with a different distribution when compared with the expression in normal synovial tissue. B-cell clones from rheumatoid synovial tissue thus exhibit a specificity for bacterial HSP 60, and a monospecific rabbit serum against this HSP shows strong reactivity within the rheumatoid synovial tissue. It may be postulated that a humoral HSP 60 response, initially directed against an infectious agent, could react with cross-reactive epitopes of rheumatoid synovial tissue or with self-HSP perpetuating the local inflammatory process.