title: Lyb-5+ B cells can be activated by major histocompatibility complex-restricted as well as unrestricted activation pathways.
abstract: It has previously been demonstrated that B cells can be activated through two distinct T helper (Th) cell-dependent pathways, one requiring both carrier-hapten linkage and MHC-restricted T-B interaction and the other requiring neither. In addition, it has been shown that different B cell subpopulations exist and that these subpopulations differ in their activation requirements. Previous studies demonstrated that resting B cells containing an Lyb-5+ subpopulation were activated by MHC-unrestricted T cell signals, whereas resting Lyb-5- B cells were activated only through MHC-restricted T-B interaction. It was suggested that this difference resulted from the ability of Lyb-5+ but not Lyb-5-B cells to respond to soluble MHC-unrestricted Th signals. Because Lyb-5+ B cells were responsive in these previous experiments to MHC-unrestricted Th signals, it could not be determined whether Lyb-5+ B cells were also responsive to MHC-restricted Th signals. Consequently, the present study was undertaken to directly address the question of whether Lyb-5+ B cells can be activated under appropriate conditions by MHC-restricted as well as unrestricted T cell-B cell interactions. It was found that unprimed normal B cells (containing Lyb-5+ and Lyb-5-B cells) but not unprimed xid-defective populations (Lyb-5- only) can be activated by cloned KLH-specific and MHC-restricted Th cells in response to either high or low concentrations of TNP-KLH. The IgM response of Lyb-5+-containing B cells to a high concentration of antigen (10 micrograms/ml) was MHC unrestricted, whereas the IgM response of unprimed Lyb-5+ B cells to a low concentration of antigen (0.001 micrograms/ml) was MHC restricted. Thus, unprimed Lyb-5+ B cells can be activated through both MHC-restricted and unrestricted pathways. It was further demonstrated that the activation requirements of Lyb-5+ and Lyb-5- B cells differed even for MHC-restricted B cell activation.
mesh_terms: D000818:Animals; D000950:Antigens, Ly; D001402:B-Lymphocytes / Q000145:classification / Q000276:immunology* / Q000378:metabolism; D002352:Carrier Proteins / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D006183:H-2 Antigens / Q000235:genetics*; D006241:Haptens / Q000276:immunology; D007075:Immunoglobulin M / Q000096:biosynthesis; D008213:Lymphocyte Activation; D008211:Lymphocyte Cooperation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D010641:Phenotype; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D000950:Antigens, Ly; D002352:Carrier Proteins; D006183:H-2 Antigens; D006241:Haptens; D007075:Immunoglobulin M