ANALYSIS OF IMMUNOGLOBULIN GAMMA HEAVY-CHAIN EXPRESSION IN SYNOVIAL TISSUE OF A PATIENT WITH RHEUMATOID-ARTHRITIS

Objective. To gain insight into mechanisms underlying local immune responses in rheumatoid arthritis (RA), we analyzed the utilization of variable-region heavy chain (V(H)), diversity (D(H)), and joining (J(H)) gene segments expressed in synovial tissue of a patient with RA. Methods. An unrestricted complementary DNA (cDNA) library was generated from unselected cells extracted from synovial tissue obtained at the time of joint replacement. Southern blot analysis for V(H), J(H), and Cgamma subclass utilization was performed on the first 50 Cgamma- and J(H)-positive recombinants for which phage DNA was isolated. Eighteen of the clones were selected at random for sequence analysis. The VH gene segments were compared with an extensive database of germline and cDNA sequences. Results. All transcripts utilized gene segments from the V(H)1 (28%), V(H)3 (56%), and V(H)4 (15%) families. There was a predominance of J(H)4, J(H)5, and J(H)6 gene segment utilization. Fourteen of 18 randomly sequenced clones contained sufficient V(H)-region information for analysis. Eight (57%) were most closely related to V(H) gene segments that are preferentially expressed in human fetal liver or that encode antibodies with self-reactivity. The variable domains were heavily mutated, and replacement-to-silent substitution ratios (R:S ratios) in the antigen-binding domains (complementarity-determining regions [CDRs]) were disproportionately high. CDR3 lengths were quite variable, due to extensive N-region addition and 5'-exonuclease activity in the V(H)-D(H)-J(H) joins. Conclusion. Plasma cells in this synovial tissue sample appear to express V(H) gene segments that are preferentially utilized during fetal development or in autoantibodies. The J(H) repertoire is similar to that seen in adult peripheral blood lymphocytes, but much different from that found during fetal development. The large number of somatic mutations and the high R:S ratios in the CDRs suggest an antigen-driven response.