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 res ponses in rheumatoid arthritis (RA), we analyzed the utilization of va riable-region heavy chain (V(H)), diversity (D(H)), and joining (J(H)) gene segments expressed in synovial tissue of a patient with RA. Meth ods. An unrestricted complementary DNA (cDNA) library was generated fr om unselected cells extracted from synovial tissue obtained at the tim e of joint replacement. Southern blot analysis for V(H), J(H), and Cga mma 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 predomi nance 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 informa tion for analysis. Eight (57%) were most closely related to V(H) gene segments that are preferentially expressed in human fetal liver or tha t encode antibodies with self-reactivity. The variable domains were he avily mutated, and replacement-to-silent substitution ratios (R:S rati os) in the antigen-binding domains (complementarity-determining region s [CDRs]) were disproportionately high. CDR3 lengths were quite variab le, 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 ti ssue sample appear to express V(H) gene segments that are preferential ly utilized during fetal development or in autoantibodies. The J(H) re pertoire is similar to that seen in adult peripheral blood lymphocytes , but much different from that found during fetal development. The lar ge number of somatic mutations and the high R:S ratios in the CDRs sug gest an antigen-driven response.