The influence of CD40–CD154 interactions on the expressed human VH repertoire: analysis of VH genes expressed by individual B cells of a patient with X-linked hyper-IgM syndrome

Analysis of the VHDJH repertoire of peripheral blood IgM+ B cells from a patient with X-linked hyper-IgM syndrome (X-HIgM) was undertaken to determine whether the distribution of VH families in the productive repertoire might be regulated by in vivo CD40–CD154 interactions. The distribution of VH genes in the non-productive repertoire of IgM+ B cells was comparable in X-HIgM and normals. Unlike the normal productive VH repertoire, however, in the X-HIgM patient the VH4 family was found at almost the same frequency as the VH3 family. This reflected a diminution in the positive selection of the VH3 family observed in normals and the imposition of positive selection of the VH4 family in the X-HIgM patient. Unique among the VH3 genes, VH3-23/DP-47 was positively selected in both normals and the X-HIgM patient. No major differences in the usage of JH or D segments or the complementarity-determining region (CDR) 3 were noted, although the foreshortening of the CDR3 noted in the mutated VH rearrangements of normals was absent in the X-HIgM patient. Finally, a minor degree of somatic hypermutation was noted in the X-HIgM patient. These results have suggested that specific influences on the composition of the VH repertoire in normals require CD40–CD154 interactions.