Differential Effects of Selection and Somatic Hypermutation on Human Peripheral CD5

To analyze the immunoglobulin repertoire of human IgM 1 B cells and the CD5 1 and CD5 2 subsets, individual CD19 1 / IgM 1 /CD5 1 or CD5 2 B cells were sorted and non-productive as well as productive V H gene rearrangements were amplified from genomic DNA and sequenced. In both subsets, the V H 3 family was overrepresented largely as a result of preferential usage of a small number of specific individual family members. In the CD5 1 B cell subset, all other V H families were found at a frequency expected from random usage, whereas in the CD5 2 population, V H 4 appeared to be overrepresented in the nonproductive repertoire, and also negatively selected since it was found significantly less often in the productive compared to the nonproductive repertoire; the V H 1 family was significantly diminished in the productive rearrangements of CD5 2 B cells. 3-23/DP-47 was the most frequently used V H gene segment and was found significantly more often than expected from random usage in productive rearrangements of both CD5 1 and CD5 2 B cells. Evidence for selection based on the D segment and the J H gene usage was noted in CD5 1 B cells. No differences were found between the B cell subsets in CDR3 length, the number of N-nucleotides or evidence of exonuclease activity. Somatically hypermutated V H DJ H rearrangements were significantly more frequent and extensive in CD5 2 compared to CD5 1 IgM 1 B cells, indicating that IgM 1 memory B cells were more frequent in the CD5 2 B cell population. Of note, the frequency of specific V H genes in the mutated population differed from that in the nonmutated population, suggesting that antigen stimulation imposed additional biases on the repertoire of IgM 1 B cells. These results indicate that the expressed repertoire of IgM 1 B cell subsets is shaped by recombinational bias, as well as selection before and after antigen exposure. Moreover, the influences on the repertoires of CD5 1 and CD5 2 B cells are significantly different, suggesting that human peripheral blood CD5 1 and CD5 2 B cells represent different B cell lineages, with similarities to murine B-1a and B-2 subsets, respectively. ( J. Clin. Invest. 1997. 99:2488–2501.)