title: Two phenotypically distinct suppressor T cell subpopulations inhibit the induction of B cell differentiation by phytohemagglutinin.
abstract: Human B lymphocytes can be induced to differentiate into antibody-secreting plasma cells by Leu-3+ T lymphocytes stimulated with pokeweed mitogen (PWM), a polyclonal T cell activator. In contrast, other polyclonal T cell mitogens, such as phytohemagglutinin (PHA), also activate Leu-3+ T cells but are relatively ineffective inducers of B cell differentiation. We have performed a series of experiments to investigate the mechanism underlying this apparent paradox. When human B cells were cultured with unfractionated T cells and PWM or PHA, only PWM was able to induce plasma cell formation and immunoglobulin (Ig) secretion. However, when the T cells were treated with mitomycin C (MMC) before culture, both PWM and PHA were able to induce significant B cell differentiation. These data indicated that both mitogens were able to activate the helper T cells required for B lymphocyte differentiation and suggested that MMC-sensitive suppressor T cells were responsible for inhibiting the induction of antibody-secreting cells by MMC-untreated T cells stimulated with PHA. Phenotypic analysis of the T cells capable of suppressing PHA-induced B cell differentiation revealed that small numbers of either Leu-2+ or Leu-3+ T cells could profoundly suppress the B cell differentiation induced by PHA. In contrast, significant suppression of PWM-stimulated B cell differentiation was observed only with relatively large numbers of Leu-2+ T cells. These data confirm previous reports that OKT4+/Leu-3+ T cells can suppress human B cell differentiation and indicate that the difference in B cell differentiation induced by PWM and PHA with MMC-untreated T cells is largely a reflection of the relative potency of these mitogens to activate these phenotypically distinct suppressor T cell subpopulations.
mesh_terms: D000921:Antibody-Producing Cells / Q000166:cytology*; D001402:B-Lymphocytes / Q000166:cytology*; D002454:Cell Differentiation; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D016685:Mitomycin; D008937:Mitomycins / Q000494:pharmacology; D010641:Phenotype; D010835:Phytohemagglutinins / Q000494:pharmacology*; D011043:Pokeweed Mitogens / Q000494:pharmacology; D006377:T-Lymphocytes, Helper-Inducer / Q000187:drug effects / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000145:classification* / Q000276:immunology
chemical_list: D008937:Mitomycins; D010835:Phytohemagglutinins; D011043:Pokeweed Mitogens; D016685:Mitomycin