title: Human B cell activation and cell cycle progression: stimulation with anti-mu and Staphylococcus aureus Cowan strain I.
abstract: The responses of resting human B lymphocytes to a variety of activation signals were studied. Human tonsillar B lymphocytes were separated according to size by countercurrent elutriation. The small B lymphocytes were then stimulated in vitro with various concentrations of anti-mu antibody in the presence or absence of B cell growth factor (BCGF) or with Staphylococcus aureus Cowan strain I (SAC). Cellular volume changes and RNA synthesis were measured over the first 24 h of stimulation and were similar with either 15 micrograms/ml of anti-mu, 100 micrograms/ml of anti-mu, or SAC. In the subsequent 24 h, however, substantial increases occurred in the amount of RNA synthesis and cell enlargement only in those cultures stimulated with 100 micrograms/ml of anti-mu or SAC, but not in the cultures stimulated with 15 micrograms/ml of anti-mu. The addition of BCGF to those cultures stimulated with 15 micrograms/ml of anti-mu did not alter the increases in cellular volume and RNA synthesis found 24 h after stimulation with anti-mu alone. However, over the subsequent 24 h, the presence of BCGF in culture enhanced both B cell volume changes and RNA synthesis, when compared to cultures stimulated with 15 micrograms/ml of anti-mu alone. In addition, BCGF enhanced DNA synthesis in cultures stimulated with low and high concentrations of anti-mu. DNA content changes following stimulation with anti-mu, anti-mu plus BCGF, and SAC were also measured using propidium iodide staining and flow cytometry. Optimal concentrations of anti-mu induced 20% of the resting B cells to enter S phase, while optimal concentrations of anti-mu plus BCGF or SAC induced approximately 40%. Finally, prestimulation of resting B cells for 24 h with a low concentration of anti-mu, sufficient for cell enlargement but not S phase progression, allowed for rapid entrance of the prestimulated B cells into S phase when a high concentration of anti-mu or SAC was added. These findings suggest the existence of a control point in the progression of human B cells through the cell cycle. This control point is located in the G1 phase of the cycle and is reached 24 to 36 h after a surface immunoglobulin-mediated stimulus.
mesh_terms: D000888:Antibodies, Anti-Idiotypic / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D004247:DNA / Q000096:biosynthesis / Q000378:metabolism; D006133:Growth Substances / Q000502:physiology; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000276:immunology*; D007148:Immunoglobulin mu-Chains / Q000276:immunology*; D015847:Interleukin-4; D007399:Interphase; D007700:Kinetics; D008213:Lymphocyte Activation; D008222:Lymphokines / Q000502:physiology; D012313:RNA / Q000096:biosynthesis; D013203:Staphylococcal Infections / Q000276:immunology*; D013209:Staphylococcal Vaccines / Q000494:pharmacology
chemical_list: D000888:Antibodies, Anti-Idiotypic; D006133:Growth Substances; D007143:Immunoglobulin Heavy Chains; D007148:Immunoglobulin mu-Chains; D008222:Lymphokines; D013209:Staphylococcal Vaccines; D015847:Interleukin-4; D012313:RNA; D004247:DNA