| Abstrakt: |
We have previously demonstrated that stimulation of B cells by multivalent membrane Ig cross-linking, using dextran-conjugated anti-IgD mAb (αδ-dex), in the presence of cytokines, is an in vitro model for T cell-independent type 2 (TI-2) Ig secretory responses. Earlier studies have shown that IL-4 enhances IgM secretion upon stimulation with αδ-dex plus IL-5 and induces IgG1 isotype-switching, without altering the proliferative response to αδ-dex. Here we show that IL-4 can have both stimulatory and inhibitory effects on αδ-dex-induced Ig secretion. Both the kinetics and time of exposure to IL-4, and the nature of the cytokine additions, Th1 versus Th2, determine whether stimulation or inhibition is observed. Preincubation of sort-purified B cells with IL-4 caused a 6- to 8-fold increase in Ig secretory responses to subsequent stimulation with αδ-dex plus IL-1, IL-2 or a combination of both. However, the continued presence of IL-4 during B cell stimulation suppressed responses to all cytokine combinations tested, except for those which included IL-5. Of 11 cytokines tested, only IL-4 showed this dual effect of enhancement and suppression. The stimulatory effect of IL-4 required a minimum of 4 h of preincubation and could be inhibited by the addition of IFN-γ. Thus stimulation of non-MHC class II-dependent T or non-T cells by multivalent antigens to secrete IL-4 may regulate the response to these antigens, such that early and brief exposure of B cells to IL-4 will enhance a subsequent TI-2 response in the presence of Th1-dependent cytokines, while continuous exposure will result in inhibition of the response. |
