ANALYSIS OF V-K GENES IN RHEUMATOID-ARTHRITIS (RA) SYNOVIAL B-LYMPHOCYTES PROVIDES EVIDENCE FOR BOTH POLYCLONAL ACTIVATION AND ANTIGEN-DRIVEN SELECTION

To define mechanisms of sustained activation of synovial B lymphocytes in RA, we studied hybridomas established from the local synovial B ce ll repertoire of two RA patients for V-kappa gene expression and for a ntigen-binding specificity. The analyses revealed that members of the main V-kappa families (I, II and III) were utilized at frequencies con sistent with random V-kappa gene family use. Furthermore, although the hybridomas expressed genes frequently seen in response to other self- and exogenous antigens, only one VkappaI- and two of three VkappaIII- expressing hybridomas exhibited reactivity with self-antigens. Nucleot ide sequence analysis revealed that all hybridomas, with the exception of rheumatoid factor (RF)-producing hybridomas, expressed V-kappa gen es highly related to known germ-line genes (99.3-100% homology) and th at diversity was generated by deletions and random nucleotide insertio ns at the V-kappa-J(kappa) junction. Examination of the few nucleotide changes seen within the V-kappa genes revealed a predominance of sile nt to replacement changes. Moreover, most of these changes can be attr ibutable either to allotypic variations or to limited random nucleotid e replacements independent of antigen selection. In contrast, one IgG- RF (B4D8) exhibited predominantly replacement nucleotide changes in th e complementarity-determining regions, suggestive of antigen-driven se lection. The random expression of immunoglobulin variable region genes with no, or little, evidence of mutation in the synovial B lymphocyte repertoire, including natural polyreactive antibodies, alongside muta ted IgG-RF, suggest that both polyclonal activation and antigen-driven responses occur in RA synovia.