A functional B cell receptor transgene allows efficient IL-7-independent maturation of B cell precursors.
IL-7 supports the proliferation of B cell precursors, but inhibits their maturation to mature surface IgM+ (sIgM+) B cells. This inhibition is thought to occur by direct or indirect down-regulation of recombinase genes, preventing the B cells from undergoing Ig light chain rearrangements. To directly analyze the IL-7 inhibitory effects, we studied B cell development and maturation in B cells bearing a transgenic (Tg) B cell receptor (BCR). We show here that proliferation of Tg B cell precursors is IL-7 dependent both in vivo and in vitro and is comparable to that of non-Tg B cell precursors. Tg B cell precursors grown on stroma and IL-7 expressed sIgM on >90% of the cells, and a large proportion of these cells coexpressed additional maturation markers such as IgD, CD23, CD21, and L-selectin, indicating that IL-7 does not inhibit maturation of Tg B cell precursors. The presence of the Tg inhibited V(D)J recombination in the cultured cells, as very low levels of recombination activating genes 2 (RAG-2) expression and endogenous V-Jkappa DNA rearrangements were found. Expression levels of RAG mRNAs were not significantly changed after removal of IL-7 from the in vitro Tg B cell cultures. In contrast, we found that IL-7 inhibited maturation of non-Tg B cell precursors and that removal of IL-7 resulted in a significant increase in RAG-2 expression and kappa rearrangements, thus allowing the B cells to express sIgM and to mature. These results suggest that IL-7-mediated inhibition of Ig gene rearrangement blocks maturation of B cell precursors and that the presence of Tg BCR efficiently circumvents this inhibition.
Melamed
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Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206, USA.
Kench
J A
JA
Grabstein
K
K
Rolink
A
A
Nemazee
D
D
D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000096:biosynthesis; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D001667:Binding, Competitive / Q000276:immunology; D001853:Bone Marrow / Q000276:immunology; D001854:Bone Marrow Cells; D002454:Cell Differentiation / Q000276:immunology; D015322:Gene Rearrangement, B-Lymphocyte; D016654:Genes, RAG-1 / Q000276:immunology; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D007075:Immunoglobulin M / Q000096:biosynthesis; D015851:Interleukin-7 / Q000502:physiology*; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology
D000944:Antigens, Differentiation, B-Lymphocyte; D007075:Immunoglobulin M; D015851:Interleukin-7; D011947:Receptors, Antigen, B-Cell