The DJ(H) complex remains active in recombination to V(H) segments after the loss of μ-chain expression in μ-positive pre-B cells

AT11-2 is an Abelson virus-transformed B precursor cell line which is capable of differentiating Ig^- from μ⁺ cells via functional recombination of V(H) segments to preexisting DJ(H) complexes. We describe here that after a μ⁺ subclone (VDJ⁺/DJ) generated from Ig^- AT11-2 (DJ/DJ) cells by in vitro functional V(H) to DJ(H) recombination subsequently lost μ-chain expression either by the recombination of a pseudo V(H) segment to the V(H)DJ(H)⁺ allele or by the deletion of V(H)DJ(H)⁺ allele, a novel productive joining of V(H) segments to the preexisting DJ(H) complex occurred. These results indicated that V(H) to V(H)DJ(H) rearrangement was not suppressed in μ-chain producing cells and that the DJ(H) complexes still remained active in the recombination to V(H) segments after the loss of μ-chain expression. Our results may also suggest that V(H) to DJ(H) rearrangement, but not V(H) to V(H)DJ(H) rearrangement, is suppressed in μ-chain producing cells to maintain allelic exclusion. Our cell differentiation system should continue to be valuable for elucidating the mechanism of suppression and associated implications regarding allelic exclusion.