Intracellular signaling events associated with the induction of DNA synthesis in human B lymphocytes. II. Different pathways triggered by IL-2 and IL-4

1alpha,25-dihydroxyvitamin D3 inhibits anti-CD40 plus IL-4-mediated IgE production in vitro

In the present study, we examined whether anti-CD40+IL-4-mediated B cell proliferation and immunoglobulin synthesis is affected by vitamin D (VD) and its low-hypercalcemic analogue EB1089 in Bcells from healthy donors. Analysis of vitamin D receptor (VDR) expression showed that only anti-CD40+IL-4-stimulated, but not resting B cells express VDR. Studies on B cell proliferation revealed that anti-CD40+IL-4-mediated proliferation of B cells was not affected by VD or EB1089. By contrast, IgE synthesis was markedly inhibited by both, VD and EB1089, starting at concentrations from 10(-10) M for VD and 10(-12) M for EB1089, with maximal inhibition at 10(-6) M (VD 85.5+/-9.7%; EB1089 77.3+/-10.8%). The production of the other Ig (IgA and IgG) was not significantly inhibited by VD after anti-CD40+IL-4 stimulation, and IgM production was only slightly reduced (18.7+/-7.9%). These observations were confirmed by intracellular staining of the different isotypes in B cells after anti-CD40+IL-4 stimulation, which showed a strong reduction of IgE(+) cells in the presence of VD. Analyses of molecules that are known to affect IgE production (CD23 and IL-6) revealed that these are not involved in VD-dependent inhibition of IgE production. By contrast, epsilon germ-line transcription was inhibited by VD (41.2+/-26.1%; n=5), as was NF-kappaB (p50 and p65) protein expression in stimulated cells. These data show that VD and its analogue EB1089 inhibit IgE production of anti-CD40+IL-4-stimulated B cells in vitro. The involved mechanism includes epsilon germ-line transcription, NF-kappaB activation and switch recombination suggesting that complex mechanisms of VD action in anti-CD40+IL-4-stimulated B cells are responsible.

Differential effects of fluoxetine on murine B-cell proliferation depending on the biochemical pathways triggered by distinct mitogens

The effect of fluoxetine on mitogen-induced B-cell proliferation was studied. In particular, we analyzed the influence of fluoxetine on the signal transduction pathways triggered after stimulation with lipopolysaccharide (LPS) and anti-immunoglobulin M antibodies (anti-IgM). We showed that fluoxetine had a dual effect on anti-IgM-stimulated B-cell proliferation: at optimal anti-IgM concentration, fluoxetine inhibited proliferation, whereas at suboptimal anti-IgM concentration, the drug enhanced proliferation. Fluoxetine exerted only an inhibitory effect on LPS-induced B-cell proliferation. Calcium influx seemed to be involved in these effects.

Activation of pp70/85 S6 kinases in interleukin-2-responsive lymphoid cells is mediated by phosphatidylinositol 3-kinase and inhibited by cyclic AMP

Activation of phosphatidylinositol 3-kinase (PI3K) and activation of the 70/85-kDa S6 protein kinases (alpha II and alpha I isoforms, referred to collectively as pp70S6k) have been independently linked to the regulation of cell proliferation. We demonstrate that these kinases lie on the same signalling pathway and that PI3K mediates the activation of pp70 by the cytokine interleukin-2 (IL-2). We also show that the activation of pp70S6k can be blocked at different points along the signalling pathway by using specific inhibitors of T-cell proliferation. Inhibition of PI3K activity with structurally unrelated but highly specific PI3K inhibitors (wortmannin or LY294002) results in inhibition of IL-2-dependent but not phorbol ester (conventional protein kinase C [cPKC])-dependent pp70S6k activation. The T-cell immunosuppressant rapamycin potently antagonizes IL-2-(PI3K)- and phorbol ester (cPKC)-mediated activation of pp70S6k. Thus, wortmannin and rapamycin antagonize IL-2-mediated activation of pp70S6k at distinct points along the PI3K-regulated signalling pathway, or rapamycin antagonizes another pathway required for pp70S6k activity. Agents that raise the concentration of intracellular cyclic AMP (cAMP) and activate cAMP-dependent protein kinase (PKA) also inhibit IL-2-dependent activation of pp70S6k. In this case, inhibition appears to occur at least two points in this signalling path. Like rapamycin, PKA appears to act downstream of cPKC-mediated pp70S6k activation, and like wortmannin, PKA antagonizes IL-2-dependent activation of PI3K. The results with rapamycin and wortmannin are of added interest since the yeast and mammalian rapamycin targets resemble PI3K in the catalytic domain.