Comparable impact of mutational and selective influences in shaping the expressed repertoire of peripheral IgM+/CD5- and IgM+/CD5+ B cells.

Somatic hypermutation and subsequent selection play a significant role in shaping the peripheral B cell repertoire. This repertoire is composed of CD5+ (5%) and CD5- B cells (95%) which are known to traffic through different lymphoid compartments. Previous studies have shown that V(H) gene usage by CD5+ and CD5- B cells is similar, although mutations are more frequent in the latter. However, the effect of mutation and subsequent selection on the expressed V(H) repertoire of CD5+ and CD5- B cells has not been delineated in detail. This study, therefore, analyzed the mutational pattern of individual IgM+/CD5+ and IgM+/CD5- B cells. In both populations, mutations can occur without heavy chain isotype switching. Despite the differences in mutational frequency, the patterns of mutation and subsequent selection were comparable in CD5+ and CD5- B cells. These results imply that although mutations are more frequent in CD5- B cells, the overall mechanisms governing somatic hypermutation and subsequent positive and negative selection are similar in CD5+ and CD5- B cells.