Ly-6A/E is a phosphatidylinositol-linked membrane protein which mediates murine T and B cell signalling. IFN-gamma, IFB-alpha/beta, LPS, and IL-4 have all been reported to induce or upregulate Ly-6A/E by normal lymphocytes. Since no systematic study has addressed the stimulant selectivity of Ly-6A/E expression by murine lymphocytes nor investigated its induction and regulation during primary in vivo immune responses we analyzed in vitro Ly-6A/E expression after murine stimuli and during a number of distinct in vivo immunizations. We show that LPS induces B cell Ly-6A/E in vitro by stimulating the release of IFN-alpha/beta by 'contaminating' adherent cells. In the presence of anti-IFN-gamma + anti-IFN-alpha/beta antibodies, no Ly-6A/E was induced upon addition of multiple cytokines, including IL-4, or mitogenic doses of anti-Ig antibody. Furthermore, IFN-gamma-containing, CD4+ T cell (Th1) supernatants potently induced Ly-6A/E by murine B cells whereas IL-4-containing (Th2) supernatants were either weak or ineffective; anti-IFN-gamma + anti-IFN-alpha/beta inhibited Ly-6A/E induction by both Th1 and Th2 supernatants. Immunization of mice with Brucella abortus or poly (I).poly (C) resulted in induction of Ly-6A/E expression by virtually all B and T cells, whereas injection of G alpha M delta led to peak induction of Ly-6A/E by approximately 50% of both B and T cells. Lymphocytes from mice infected with the nematode parasites Nippostrongylus brasiliensis or Heligmosomoides polygyrus expressed no Ly-6A/E.(ABSTRACT TRUNCATED AT 250 WORDS)
We previously demonstrated that anti-IgD antibodies conjugated to dextran (alpha delta-dex) were a potent co-stimulus for Ig secretion by resting murine B cells in the presence of cytokines. However, although alpha delta-dex stimulated the secretion of most Ig isotypes it selectively failed to costimulate IgE production even in the presence of high concentrations of IL-4. Earlier reports indicated that unconjugated anti-IgM, which was not an effective costimulus for Ig secretion, in fact inhibited Ig production induced by LPS. We determined the effect of alpha delta-dex, at concentrations that costimulated cytokine-induced Ig secretion, on Ig production by LPS- or T cell-activated B cells, and whether IgE production was affected in a selective manner. We observed that alpha delta-dex inhibited Ig isotype production (IgE > IgG > IgM) by LPS-activated B cells, while further stimulating their proliferation. This effect of alpha delta-dex was mediated directly at the level of the B cell and was accompanied by a comparable inhibition in Ig class switching, as assessed by flow cytometric analysis of membrane Ig isotype-positive cells. The inhibitory effects of alpha delta-dex on LPS-induced Ig secretion and class switching occurred at 1000-fold lower concentrations of anti-IgD than that reported necessary for inhibition by unconjugated anti-IgM. Whereas IL-4 + IL-5 costimulated Ig isotype production by alpha delta-dex-activated cells, the further addition of LPS led to a marked ablation of the Ig secretory response indicating the cross-inhibitory effects of these two modes of B cell activation. By contrast, alpha delta-dex augmented IgM and IgG1 secretion by resting B cells stimulated with either an anti-CD3-activated CD4+ Th2 clone or with activated T cell membranes in combination with IL-4 + IL-5. However, alpha delta-dex potently inhibited T cell-mediated IgE secretion. These findings underscore the existence of, and demonstrate a number of novel interrelationships between, three distinct pathways of B cell differentiation induced by different modes of activation. Further, the observation that pg/ml quantities of alpha delta-dex selectively inhibits T cell-induced IgE production in vitro suggests a novel strategy to down-regulate this Ig isotype in vivo.
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