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98 Stromal Cell-Derived Factor-1alpha(SDF-1alpha>) Inhibited HIV-1 Envelope Glycoprotein-Induced Apoptosis in Human B Lymphocytes
C. Patke* and W. Shearer
Baylor Coll. of Med. and Texas Children’s Hosp., Houston, USA
Background: HIV-1 infection results in an imbalance in the production of immunoregulatory cytokines and dysfunctional B-cell regulation. The dysfunction in the B-cell population of HIV-1-infected individuals may be paralleled by priming of B cells for apoptotic cell death. As programmed cell death is regulated in part by Bcl-2, we present evidence of rescue from HIV-1 gp120-induced apoptosis in B cells by the chemokine, SDF-1alpha, natural ligand of the HIV-1 coreceptor, CXCR4.
Methods: Regulation of B-cell apoptosis was investigated using highly purified HIV-1 seronegative donor CD40-activated human B lymphocytes. Analyses of the apoptotic pathways, APO-1/Fas (CD95) and Bcl-2 were made by flow cytometry, ELISA, colorimetric, and protein assays.
Results: Flow cytometric analysis revealed no Bcl-2 expression in resting B cells, but Bcl-2 expression was induced by CD40 stimulation at 48 h (51%) (p < 0.01). SDF-1alpha?(100 ng/ml) augmented the CD40-induced Bcl-2 expression (120%) (p < 0.01). The HIV-1 envelope glycoprotein gp120 (100 ng/ml) down-regulated Bcl-2 expression (39%) (p < 0.01). Bcl-2 protein levels measured by ELISA increased in the presence of SDF-1alpha (10(1,000 ng/ml) 3-fold at 1,000 ng/ml (p < 0.01). Addition of an anti-CXCR4 antibody resulted in the abrogation of the SDF-1alpha-induced apoptosis rescue by enhanced Bcl-2 expression. IL-10, a B-cell immunomodulator up-regulated during HIV-1 infection, decreased the CD40-induced Bcl-2 expression (35%) (p < 0.01). IL-10 exerted no effect on SDF-1alpha-induced Bcl-2 expression. gp120 (100 ng/ml) up-regulated receptor expression of the APO-1/Fas (CD95) molecule (129%) (p < 0.01) and SDF-1alpha (10 ng/ml) down-regulated CD95 expression (34%) (p < 0.01). ELISA determination of APO-1/Fas levels correlated with the flow cytometric data. HIV has been shown to induce a caspase-dependent apoptotic signaling pathway through CXCR4. Addition of the caspase-3 inhibitor DEVD-FMK abolished the SDF-1alpha inhibition of gp120-induced apoptosis. Specificity of the gp120- and SDF-1alpha-induced events was demonstrated by the abrogation of these effects by neutralizing anti-gp120 or anti-SDF-1alpha antibody.
Conclusions: These data suggest the potential for therapeutic approaches involving SDF-1alpha to reduce HIV-1-induced B-cell apoptosis through the CXCR4-caspase-dependent signaling pathway and restoration of Bcl-2 function.
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