CLONALLY-RELATED IMMUNOGLOBULIN V-H DOMAINS AND NONRANDOM USE OF D-H GENE SEGMENTS IN RHEUMATOID-ARTHRITIS SYNOVIUM

Background: Synovia of patients with long-standing rheumatoid arthriti s (RA) are typically infiltrated with B lymphocytes and plasma cells t hat secrete large amounts of immunoglobulin. The CDR3 of an immunoglob ulin heavy chain is composed of the V-H-D-H-J(H) join, with interposed N region addition, and thus defines clonal relatedness. Furthermore, the CDR3 lies at the center of the antigen binding site, so its length and composition influence antigen binding. We sought definitive evide nce of an antigen-driven B cell response (i.e., clones derived from th e same V-H, D-H, and J(H) gene segments with shared somatic mutations) in RA synovial mRNA transcripts, and to characterize CDR3 intervals a t the target of inflammation in this autoimmune disease. Materials and Methods: We screened a cDNA library generated from unselected cells f rom the knee joint of a 62-year-old white female with long-standing RA . This technique does not have the potential bias of selecting for ant ibodies that express a particular reactivity such as rheumatoid factor . C gamma recombinants were sequenced and progenitor V-H, D-H, and J(H ) gene segments were assigned and somatic mutations determined by comp arison to germline sequences. Analyses of D-H reading frame utilizatio n and hydropathy characteristics of CDR3s were performed. Results: Two of 67 recombinants were derived from the same V-H (V3-11) and J(H) ge ne segments, demonstrated shared mutations, and contained nearly ident ical V-H- D-H-J(H) joins, including N region addition. Three other rec ombinants contained identical sequence throughout the variable domain. We also found preferential utilization of a limited number of V-H and D-H gene segments and marked preference for a D-H reading frame encod ing predominantly hydrophilic residues. Conclusions: Analysis of expre ssed heavy chain variable domains strongly supports the hypothesis tha t the B cell response in RA synovium is at least in part antigen drive n and oligoclonal.