Biased V-H gene usage in early lineage human B cells: Evidence for preferential Ig gene rearrangement in the absence of selection

Certain V-H genes are predominantly expressed in mature B cells. We hypothe sized that several, mutually nonexclusive V(H)(-)dependent mechanisms opera ting at distinct stages during B cell development may be responsible for ov errepresentation of these V-H genes, In the present study, we have assessed whether one of the mechanisms involves preferential rearrangement at the p ro-Il cell stage. The frequency of individual V(H)4 and V(H)3 genes in rear rangement libraries from FAGS-purified human CD34(+)/CD19(+) pro-B and CD34 (-)/CD19(+) pre-B cells was assessed. The in-frame and out-of-frame rearran gements from both cell populations were analyzed using a high resolution PA GE system. The frequencies of individual V-H gene segments among out-of-fra me rearrangements from pro-B cells were determined, because these frequenci es should reflect only processes before the translation of the mu-heavy cha in and should not be biased by selection mechanisms, Our results demonstrat e that, at the pro-B cell stage, the V4-34, V4-39, and V4-59 gene segments are the most frequently rearranged V(H)4 Family genes, and the V3-23 and V3 -30 gene segments are the most frequently rearranged V(H)3 family genes. Th is finding suggests that the predominant expression of these V-H genes in p eripheral mature B cells is determined to a significant degree by their pre ferential rearrangement during V-DJ recombination.