title: Interleukin-4 enhances anti-IgM stimulation of B cells by improving cell viability and by increasing the sensitivity of B cells to the anti-IgM signal.
abstract: The lymphokine IL-4 is a potent enhancer of anti-IgM-induced B cell proliferation. Although the mechanism of this enhancement is not known, a commonly held view suggests that IL-4 acts together with anti-IgM as a costimulating factor for the activation of a subpopulation of B cells. To evaluate this hypothesis we examined the effect of IL-4 on the proportion of B cells stimulated to divide by different doses of anti-IgM using flow cytometry in combination with measurements of tritiated-thymidine incorporation. The results suggest a novel and surprisingly simple model for the mode of action of IL-4. Our analysis revealed that at high saturating anti-IgM concentrations, the proportion of live B cells which enter into S phase of the cell cycle is the same (approximately 65%) for cells cultured with or without IL-4. Cultures containing IL-4, however, exhibit a twofold increase in thymidine uptake over cultures without IL-4. This increase can be explained completely by the ability of IL-4 to enhance the viability of small dense B cells over the first 24 hr from approximately 50 to 90% of the starting cell number. Normalizing the maximum response levels obtained with and without IL-4 reveals that B cells incubated with IL-4 exhibit a 10-fold decrease in the concentration of anti-IgM required to stimulate the half-maximum proliferation level. Furthermore, evaluation of the number of cells in S phase by flow cytometry and analysis of the kinetics of cell proliferation revealed that the increased response effected by IL-4 at lower anti-IgM concentrations was due to a greater number of proliferating B cells rather than the same number of cells undergoing a faster division rate. We also found a highly nonlinear relationship between B cell number and proliferative response, implying a requirement for an additional, cell cooperation-mediated, activating signal for maximum B cell proliferation. IL-4 enhanced proliferation by the same proportion at all cell concentrations indicating that it does not replace or alter this requirement for cell cooperation. Taken together these results suggest that anti-IgM in combination with a second unidentified cell-cooperation-dependent signal leads to proliferation of up to 65% of small resting B cells. IL-4 does not provide an essential activation signal but serves to raise the sensitivity of B cells to the anti-IgM-generated signal.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, California 94304.
authors.forename: P D
authors.initials: PD
authors.lastname: Hodgkin
authors.forename: N F
authors.initials: NF
authors.lastname: Go
authors.forename: J E
authors.initials: JE
authors.lastname: Cupp
authors.forename: M
authors.initials: M
authors.lastname: Howard
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology*; D002453:Cell Cycle; D002470:Cell Survival; D003703:Demecolcine / Q000494:pharmacology; D004306:Dose-Response Relationship, Immunologic; D005434:Flow Cytometry; D015847:Interleukin-4 / Q000494:pharmacology*; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D013997:Time Factors
chemical_list: D000888:Antibodies, Anti-Idiotypic; D011947:Receptors, Antigen, B-Cell; D015847:Interleukin-4; D003703:Demecolcine