title: T cell-induced expression of membrane IgG by 70Z/3 B cells.
abstract: To study T cell regulation of B cell isotype differentiation, we determined the capacity of clonal T cell populations (hybridomas derived by fusing BW5147 with Con A-activated Peyer's patch (PP) and spleen T cells) to induce "downstream" isotype expression by the pre-B cell lymphoma 70Z/3. In initial studies, we found that 70Z/3 B cells cultured in the presence of LPS (1 microgram/ml) expressed membrane IgM (mIgM) but not membrane IgG (mIgG). In contrast, 70Z/3 B cells cultured with HAJ-3 T cells, a PP-derived T cell hybridoma (as well as other similarly derived PP and spleen hybridomas), or with HAJ-3 T cells plus LPS do express mIgG. Such expression occurred in spite of mitomycin C-induced blockage of cell proliferation, and is observed in 70Z/3 B cell subclones cultured with HAJ-3 T cells. For these reasons, it is not due to selective expansion of a small pre-switched mIgG-bearing 70Z/3 B cell subpopulation. In other studies it was shown that 70Z/3 B cells expressing mIgG after induction by HAJ-3 T cells continue to express mIgM and do not secrete IgG. Finally, exposure of 70Z/3 B cells to the macrophage factor IL 1 and the T cell factors IL 2, BSF-pl, and BCGF-II present in EL-4 cell supernatants did not result in mIgG expression. On the basis of these studies, we conclude that a clonal B cell population expressing mIgM can be induced by T cells to co-express mIgG. Because the B cells do not express mIgG unless exposed to T cells, this represents a T cell-induced isotype switch.
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D002999:Clone Cells / Q000276:immunology; D006825:Hybridomas / Q000276:immunology; D007074:Immunoglobulin G / Q000096:biosynthesis*; D007075:Immunoglobulin M / Q000096:biosynthesis; D007376:Interleukin-2 / Q000502:physiology; D008213:Lymphocyte Activation / Q000187:drug effects; D051379:Mice; D016685:Mitomycin; D008937:Mitomycins / Q000494:pharmacology; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis*; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D007074:Immunoglobulin G; D007075:Immunoglobulin M; D007376:Interleukin-2; D008937:Mitomycins; D011947:Receptors, Antigen, B-Cell; D016685:Mitomycin