Receptor revision plays no major role in shaping the receptor repertoire of human memory B cells after the onset of somatic hypermutation

Abstract

In order to determine whether V gene replacement accompanies somatic hypermutation in the germinal center (GC) reaction in the human, we analyzed V(kappa)J(kappa) and V(lambda)J(lambda) joints and the kappa-deleting element in single lambda(+) naive and post GC B cells for rearrangements at the kappa and lambda loci. Among 265 lambda(+) post GC B cells, not a single unequivocal and only two potential examples of a cell that switched to lambda light chain expression after accumulation of (unfavorable) mutations in its productive V(kappa) rearrangement were observed. Taking the PCR efficiency into account, the frequency of such cells is likely below 3 %. In addition, heavy and light chain gene rearrangements were amplified and sequenced from the oligoclonal population of IgD-only peripheral blood post GC B cells which display extensive intraclonal sequence diversity. Among 61 IgD-only B cells belonging to 15 clones with intraclonal diversity, no combination of V gene rearrangements indicating receptor revision during clonal expansion was observed. Moreover, among 124 and 49 V(H) genes amplified from IgD-only and class-switched B cells, respectively, not a single example of V(H) revision through V(H) hybrid generation was detected. These results suggest that in the human GC reaction V gene replacement either does not usually accompany somatic hypermutation or is mostly counterselected.