Mycobacterium tuberculosis Cell Wall Glycolipids Directly Inhibit CD4 + T-Cell Activation by Interfering with Proximal T-Cell-Receptor Signaling

Abstract

ABSTRACT Immune evasion is required for Mycobacterium tuberculosis to survive in the face of robust adaptive CD4 + T-cell responses. We have previously shown that M. tuberculosis can indirectly inhibit CD4 + T cells by suppressing the major histocompatibility complex class II antigen-presenting cell function of macrophages. This study was undertaken to determine if M. tuberculosis could directly inhibit CD4 + T-cell activation. Murine CD4 + T cells were purified from spleens by negative immunoaffinity selection followed by flow sorting. Purified CD4 + T cells were activated for 16 to 48 h with CD3 and CD28 monoclonal antibodies in the presence or absence of M. tuberculosis and its subcellular fractions. CD4 + T-cell activation was measured by interleukin 2 production, proliferation, and expression of activation markers, all of which were decreased in the presence of M. tuberculosis . Fractionation identified that M. tuberculosis cell wall glycolipids, specifically, phosphatidylinositol mannoside and mannose-capped lipoarabinomannan, were potent inhibitors. Glycolipid-mediated inhibition was not dependent on Toll-like receptor signaling and could be bypassed through stimulation with phorbol 12-myristate 13-acetate and ionomycin. ZAP-70 phosphorylation was decreased in the presence of M. tuberculosis glycolipids, indicating that M. tuberculosis glycolipids directly inhibited CD4 + T-cell activation by interfering with proximal T-cell-receptor signaling.