title: Major histocompatibility complex class II expression distinguishes two distinct B cell developmental pathways during ontogeny.
abstract: All mature B cells coexpress major histocompatibility complex (MHC) class II molecules, I-A and I-E, which are restriction elements required for antigen presentation to CD4+ T cells. However, the expression of class II during the early stages of B cell development has been unclear. We demonstrate here that there is a difference in the expression of class II during murine B cell development in the fetal liver and adult bone marrow (BM). These differences define two distinct B cell developmental pathways. The Fetal-type (FT) pathway is characterized by pre-B and immature IgM+ B cells generated in the fetal liver which initially lack all class II expression. In contrast, the Adult-type (AT) pathway is typified by B cells developing in the adult BM which express class II molecules from the pre-B cell stage. In vitro stromal cell cultures of sorted fetal liver and adult BM pro-B cells indicated that the difference in I-A expression during B cell development is intrinsic to the progenitors. In addition, we show that FT B cell development is not restricted to the fetal liver but occurs in the peritoneal cavities, spleens, liver, and BM of young mice up to at least 1 mo of age. The AT B cell development begins to emerge after birth but is, however, restricted to the BM environment. These findings indicate that there are two distinct B cell developmental pathways during ontogeny, each of which could contribute differentially to the immune repertoire and thus the functions of B cell subsets and lineages.
authors.affiliation: Department of Microbiology, College of Physicians & Surgeons, Columbia University, New York 10032.
authors.forename: K P
authors.initials: KP
authors.lastname: Lam
authors.forename: A M
authors.initials: AM
authors.lastname: Stall
mesh_terms: D000375:Aging / Q000276:immunology; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology*; D001853:Bone Marrow / Q000196:embryology; D001854:Bone Marrow Cells; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002454:Cell Differentiation; D002478:Cells, Cultured; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis*; D008099:Liver / Q000166:cytology / Q000196:embryology; D008221:Lymphoid Tissue / Q000276:immunology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D013234:Stem Cells / Q000276:immunology
chemical_list: D000949:Histocompatibility Antigens Class II