title: Polyclonal B cell activation by B cell differentiation factor B151-TRF2. I. Involvement of self-Ia recognition process mediated by B cells.
abstract: The present study examined the functional role of Ia antigens on B cells in polyclonal B cell activation induced by a B cell differentiation factor, B151-TRF2. The polyclonal IgM PFC responses by B151-TRF2 were inhibited by monoclonal antibodies specific for class II MHC antigens (Ia antigens) but not class I MHC antigens. Such inhibition by anti-Ia antibodies was haplotype-specific and was observed in the absence of both T cells and accessory cells. Moreover, the anti-Ia antibody-induced inhibition of the B151-TRF2 responses was not due to the blocking of binding of B151-TRF2 to the corresponding B cell receptor. A series of kinetic studies revealed that some Ia-mediated cellular activation process occurs before the resting B cells become responsive to B151-TRF2. Thus, the B151-TRF2-mediated B cell responses consist of at least two distinct phases. The early phase is an Ia-dependent but B151-TRF2-independent process, whereas the late phase is an Ia-independent but B151-TRF2-dependent process. To further characterize the functional role of Ia antigens on B cells, an additional experiment was carried out by using F1 B cells which co-dominantly express both parental Ia antigens on the surface. Interestingly, it was observed that the degree of inhibition of the B151-TRF2-mediated responses of F1 B cells by anti-parental Ia antibody was, at best, one-half that of the parental B cells, suggesting that F1 B cells may be separated into two subpopulations with the restriction specificity for the respective parental Ia antigens. To examine this possibility, (B10 X B10.BR)F1 B cells were separated into adherent and nonadherent cell populations by their ability to bind to either one of the parental B cell monolayers, and the specificity of inhibition of their responses to B151-TRF2 by anti-Ia antibodies was assessed. It was found that the responses of (B10 X B10.BR)F1 B cells adherent to the B10 B cell monolayer or the B10.BR B cell monolayer were almost completely inhibited by anti-I-Ab and anti-I-Ak antibodies, whereas those of nonadherent cells were now selectively inhibited by anti-I-Ak and anti-I-Ab antibodies, respectively. These findings are interpreted as indicating that the B151-TRF2-responsive F1 B cells consist of at least two subpopulations with the restriction specificity for either one of the parental Ia antigens.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface / Q000494:pharmacology*; D000961:Antilymphocyte Serum / Q000502:physiology; D001402:B-Lymphocytes / Q000145:classification / Q000276:immunology*; D001667:Binding, Competitive; D006183:H-2 Antigens / Q000276:immunology; D006462:Hemolytic Plaque Technique; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000276:immunology*; D007075:Immunoglobulin M / Q000096:biosynthesis; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D013997:Time Factors
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface; D000961:Antilymphocyte Serum; D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II; D007075:Immunoglobulin M