Inducing the Loss of Immunoglobulin Light Chain Production and the Rearrangement of a Previously Excluded Allele in Human Plasma B Cell Lines with Concanavalin A

Abstract

We investigated the expression of differential light chains in human B cell lines secreting immunoglobulin (Ig). When these cell lines were cultured with concanavalin A for a long period of time, a subpopulation of some but not all of these cell lines was induced to express new light chains replacing the original chain (light chain shifting). Production of the new chain, which replaces the original chain, results from a VJ rearrangement at a previously excluded allele and a dramatic reduction of the original chain transcript, although no difference was found in the level of heavy chain transcript. Recombination activating genes RAG-1 and RAG-2, which are normally expressed during specific early stages of lymphocyte development, were expressed in not only the light chain shifting-inducible lines but also in the non-inducible cells. Treatment of these Ig secreting cell lines with dibutyryl cAMP, which is known to enhance expression of the RAG genes, could not induce the creation of new light chain-producing cells from the inducible lines, suggesting that the expression of the two RAG genes is not sufficient for inducing new light chain production. Concanavalin A induced a gradual but significant production lost of the original chain in a subpopulation of the light chain shifting-inducible cells but not in the non-inducible cells. Association of new light chain production with loss of original chain raises the possibility that, when the RAG genes are expressed, concanavalin A may act on a novel intracellular mechanism controlling light chain allelic exclusion in these plasma cell lines.

Induction of Light Chain Replacement in Human Plasma Cells by Caffeine Is Independent from Both the Upregulation of RAG Protein Expression and Germ Line Transcription

“…In fact, the expression of RAG proteins was not enhanced in the HB4C5 cells when stimulated with caffeine or okadaic acid. We have previously shown that the enhancement of RAG gene expression did not induce the light chain shifting (13). Taken together, these results suggest that the induction of light chain shifting in plasma cells by caffeine is not due to an enhancement of the RAG gene expression.…”

“…Although many of the VJ recombinations at the light chain loci occur in pre-B cells, recent findings suggest that light chain gene rearrangements often continue in immature-B cells and germinal center B cells (7)(8)(9)(10)(11). We also have shown that secondary VJ recombination can occur in some human plasma cell lines when stimulated with concanavalin A (ConA) 1 (12,13).…”

“…However, there must be additional levels of regulation to determine which loci are targeted for recombination in developing lymphocytes, because endogenous Ig genes are only targeted for complete rearrangement in B lineage cells, and endogenous T cell receptor genes are only completely rearranged in T lineage cells. Plus we have also found that enhancement of RAG expression is not sufficient to induce secondary VJ rearrangement in light chain shiftinginducible human plasma cells (13,14). Therefore, expression of RAG-1 and RAG-2 is likely to be only part of the mechanism by which V(D)J recombination is activated in lymphoid cells.…”

“…These results shows that at least early steps in the V -J recombination are enhanced in HB4C5 cells stimulated by agents with phosphatase inhibitory activity. DISCUSSION We have previously found that the light chain replacement from an original to a novel chain can be induced in some human plasma cells by ConA stimulation (12,13). We call this process light chain shifting.…”

“…Both proteins were expressed in the HB4C5 cells (13). To elucidate the mechanism that couples phosphatase inhibition and light chain shifting, we evaluated the expression of RAG genes in the HB4C5 cells.…”