Secondary V(D)J rearrangements and B cell receptor-mediated down- regulation of recombination activating gene-2 expression in a murine B cell line

It has recently become clear that recombination of Ig genes is not restricted to B cell precursors but that secondary rearrangements can also occur under certain conditions in phenotypically immature bone marrow and peripheral B cells. However, the nature of these cells and the regulation of secondary V(D)J recombination in response to B cell receptor (BCR) stimulation remain controversial. In the present study, we have analyzed secondary light chain gene rearrangements and recombination activating gene (RAG) expression in the surface IgM⁺, IgD^- murine B cell line, 38C-13, which has previously been found to undergo κ light chain replacement. We find that 38C-13 cells undergo spontaneous secondary Vκ-Jκ and RS rearrangements in culture, with recombination occurring on both productive and nonproductive alleles. Both 38C-13 cells and the Id-negative variants express the RAG genes, indicating that the presence of RAG does not depend on activation via the 38C-13 BCR. Moreover, BCR cross-linking in 38C-13 cells leads to a rapid and reversible down-regulation of RAG2 mRNA. Therefore, 38C- 13 cells resemble peripheral IgM⁺, IgD^- B cells undergoing light chain gene rearrangement and provide a possible in vitro model for studying peripheral V(D)J recombination.