HEAVY-CHAIN VARIABLE REGION, LIGHT-CHAIN VARIABLE REGION, AND HEAVY-CHAIN CDR3 INFLUENCES ON THE MONOREACTIVITY AND POLYREACTIVITY AND ON THE AFFINITY OF HUMAN MONOCLONAL RHEUMATOID FACTORS

Monoreactive high affinity pathologic autoantibodies were supposed pre viously to derive through somatic mutation from polyreactive low affin ity autoantibodies that are encoded by a small set of unmutated V regi on genes in fetal and neonatal B cells. However, recent data exploring the physiologically expressed Ab repertoire and the importance of the stochastically generated heavy chain CDR3 (H-CDR3) in autoreactivity suggest that this scheme is incomplete. Here we analyzed via gene-swap ping experiments and site-directed mutagenesis the relative contributi ons of the mutations in the light chain variable region (V-L) and the heavy chain variable region (V-H) domains and of the H-CDR3 in the aut oreactivity of two IgM rheumatoid factors (RF), one a polyreactive low affinity Ab, the other a monoreactive high affinity Ab. These two RFs derived from the same V kappa III (humkv325) and V-H1, (51p1) genes, but differed from each other by a few mutations and by the structure o f the H-CDR3. The analysis of the reactivity patterns of different com binations of wild-type and in vitro engineered hybrid gene products cl early demonstrates the main influence of the H-CDR3 in the autoAb acti vity profiles. The results directly demonstrate the previously propose d hypothesis, namely, that the H-CDR3 plays a critical role in disting uishing poly- from monospecific RF. However, the data also indicate th at self polyreactivity is a very fragile property and is dependent upo n the primary structure of the V-H segment.