VH usage and somatic hypermutation in peripheral blood B cells of patients with rheumatoid arthritis (RA)

The human antibody repertoire has been demonstrated to have a marked V-gene-dependent bias that is conserved between individuals. In RA patients, certain heavy chain V genes (V-H) have been found to be preferentially used for encoding autoantibodies. To determine if such preferential use of VH genes in autoantibodies is associated with a general distortion of the V gene repertoire in RA patients, the V-H composition of peripheral blood B cells was analysed among four RA patients and four age-and sex-matched healthy controls. Usage of individual V-H genes (eight V(H)3 and three V(H)4 genes tested by hybridization with a set of gene-specific oligonucleotide probes) was highly biased among RA patients, but no evidence of a distortion in the bias was observed compared with healthy controls. However, the occurrence of somatic mutations in these V-H genes (estimated by differential hybridization with motif-specific oligonucleotide probes targeted to CDR and FR of the tested genes, and by DNA sequence analysis) was strikingly different between patients and healthy subjects. The number of V(H)3 rearrangements that had accumulated somatic mutations and the number of mutations per rearrangement were significantly elevated in three of the four RA patients. A slight but not significant elevation in mutations among rearranged V(H)4 genes was also observed in these patients. These data suggest that although usage of individual V-H genes among peripheral blood B cells is not affected by the disease, the autoimmune process may involve a significant fraction of the B cell compartment.