title: Differential effects of interleukin-2 and interleukin-4 on immunomodulatory role of platelet-activating factor in human B cells.
abstract: Platelet-activating factor (PAF), a naturally occurring phospholipid cytokine, is a potent mediator of allergic and inflammatory reactions, as well as a modulator of immune responses. In the present study we showed that PAF is involved in early B-cell activation, as demonstrated by the increased cyclic AMP (cAMP) generation by PAF in a time- and dose-dependent manner in anti-mu antibody- plus B-cell growth factor-activated normal human peripheral blood B lymphocytes. PAF also regulated differentiation by causing a biphasic response on immunoglobulin M (IgM) production with an inhibitory signal generated at 10(-6) M and a stimulatory signal generated at 10(-8) to 10(-10) M. PAF enhanced IgA secretion. The regulation exerted by PAF was shown to be specific because the addition of the PAR antagonist CV-3988 abrogated these effects and the inactive form of PAF, lyso-PAF, induced neither cAMP generation nor immunoglobulin secretion in normal human B cells. Other cytokines, interleukin-2 (IL-2) and IL-4, potent mediators of the immune response, were unable to elicit a cAMP response in B cells. However, the addition of PAF (10(-6) M) with wither IL-2 or IL-4 enhanced cAMP production above the levels enhanced by the addition of PAF alone. IL-2 or IL-4, individually, stimulated IgM production, yet costimulation with PAF resulted in a differential effect between IL-2 and IL-4. PAF down-regulated the IL-4-induced IgM secretion, whereas the IL-2-induced IgM secretion was enhanced. The presence of CV-3988 returned all valued to those obtained with IL-2 or IL-4 alone, demonstrating the specificity of PAF. These data suggest that PAF is an important B-cell immunomodulator which can interact with other leukocyte cell mediators.
authors.affiliation: Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Patke
authors.forename: C G
authors.initials: CG
authors.lastname: Green
authors.forename: W T
authors.initials: WT
authors.lastname: Shearer
mesh_terms: D000276:Adjuvants, Immunologic / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology; D000242:Cyclic AMP / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D007376:Interleukin-2 / Q000276:immunology*; D015847:Interleukin-4 / Q000276:immunology*; D010972:Platelet Activating Factor / Q000276:immunology* / Q000378:metabolism; D012680:Sensitivity and Specificity
chemical_list: D000276:Adjuvants, Immunologic; D007075:Immunoglobulin M; D007376:Interleukin-2; D010972:Platelet Activating Factor; D015847:Interleukin-4; D000242:Cyclic AMP