title: The role of immunoglobulin receptors in "cognate" T-B cell collaboration.
abstract: The functional effects of anti-Ig antibodies have been investigated, using an experimental system where B cell activation is brought about by direct and specific interactions with T helper (Th) cells without participation of surface Ig receptors on the responding B cell. We have used Th cell lines and clones directed to class II major histocompatibility complex antigens of the responding B cells, and titrated into cooperative cultures either purified rabbit anti-mouse mu, or monoclonal mouse anti-delta antibodies. Both types of antibodies greatly enhanced B lymphocyte responses to suboptimal concentrations of functionally efficient Th cells, while they had no effect in cultures containing optimal Th:B cell ratios. In contrast, helper activity by low efficiency Th was, at all Th:B cell ratios, enhanced by appropriate concentrations of anti-Ig antibodies. Anti-Ig effects were exclusively observed when B cells were the targets for "cognate" recognition by Th cells. We conclude that ligand binding to surface Ig receptors on resting B cells fails, in our experimental conditions, to overcome "linked" collaboration, but it greatly facilitates productive Th-B cell interactions. Whatever the mechanisms underlying this facilitation, the observations imply roles of surface Ig in Th-dependent B lymphocyte activation other than either passive "focusing" of antigen or activation into reactivity to soluble, unspecific factors.
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000917:Antibody Formation; D001402:B-Lymphocytes / Q000276:immunology*; D002999:Clone Cells / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D007138:Immunoglobulin delta-Chains / Q000276:immunology; D007148:Immunoglobulin mu-Chains / Q000276:immunology; D008213:Lymphocyte Activation; D008211:Lymphocyte Cooperation; D051379:Mice; D008810:Mice, Inbred C57BL; D011947:Receptors, Antigen, B-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology / Q000528:radiation effects
chemical_list: D000888:Antibodies, Anti-Idiotypic; D000949:Histocompatibility Antigens Class II; D007138:Immunoglobulin delta-Chains; D007148:Immunoglobulin mu-Chains; D011947:Receptors, Antigen, B-Cell