Deletion mapping of Ig V_H gene segments expressed in human cds b cell lines: J_H proximity is not the sole determinant of the restricted fetal V_H gene repertoire

V_H gene segments expressed in a panel of monoclonal human CD5 B cell lines have been positioned on the IgH locus by deletion mapping. The analysis yielded a relative order of V_H fragments of the V_H2, V_H4, V_H5, and V_H6 gene families that was consistent with, and provided a further refinement of existing maps of the human IgH locus. We demonstrate that four of six V_H gene segments expressed in the CDS B cell lines map >500 kb from the cluster of J_H segments. Two of the gene segments, positioned at ∼850 kb (58p2) and ∼500 kb (1-9III) from the J_H segments, respectively, belong to the previously identified small cohort of second trimester fetal V_H gene segments. The data show that J_H proximity is not the sole determinant of restricted V_H gene utilization in early human ontogeny.