A SUBGROUP OF HUMAN VH3 GERMLINE GENES THAT ENCODE A HIGH-AVIDITY SYNOVIAL RHEUMATOID-FACTOR

We have previously derived and identified a highly avid monoclonal IgM rheumatoid factor (mRF), C6, from unstimulated rheumatoid synovial ce lls (RSC). At the time, the closest VH germline gene, VH26, demonstrat ed only 88% homology with C6. To identify the germline counterpart of C6, genomic DNA from the same rheumatoid arthritis (RA) patient from w hom C6 was derived was used in the polymerase chain reaction (PCR). Fo ur of the six closely related germline genes that we sequenced had exo nic regions that were identical with the VH region of C6 cDNA. These s ix germline sequences differed in their intronic regions, suggesting t hat they were distinct, but closely related genomic sequences. To furt her evaluate the extent of these related genes we identified nine addi tional germline genes having VH-encoding exons that were 86-97% identi cal to the C6 cDNA sequence. Furthermore, we examined the polymorphic nature of the C6 VH gene using single strand conformation polymorphism (SSCP), and identified two peaks, confirming the existence of highly homologous genes. The sequence and polymorphism data suggest that: (1) the VH region of the high avidity mRF C6 was derived from an unmutate d germline gene; (2) C6 was encoded by a VH gene belonging to a set of homologous genes within the larger VH3 family; and (3) in addition to somatic rearrangements of B-cell genes and antigen-driven somatic mut ation, gene duplication and conversion events of germline genes could be important in generating diversity and polyclonality among high-affi nity pathogenic autoantibodies.