The molecular mechanism of T-cell control of Chlamydia in mice: role of nitric oxide.

T-cell mediated immunity (CMI) is crucial for protection against genital chlamydial infection in mice. To define the underlying molecular mechanism for this protection, several T-cell clones generated against the Chlamydia trachomatis agent of mouse pneumonitis (MoPn) were analysed in an in vitro model of the mucosal epithelium, the polarized epithelial-lymphocyte co-culture (PELC) system, for immunobiological functions that correlated with chlamydial inhibition. The six clones analysed were classified as protective or non-protective on the basis of their ability to cure genital chlamydial infection in syngeneic mice. The results revealed a direct relationship between the ability of a clone to protect in vivo and to inhibit the multiplication of MoPn in vitro. Also, the protective ability of a clone correlated with its capacity to elaborate relatively high levels of interferon-gamma (IFN-gamma) and to induce nitric oxide (NO) production. Moreover, neutralizing anti-IFN-gamma antibodies used alone at 50 micrograms/ml or in combination with anti-tumour necrosis-factor (TNF-alpha), and the L-arginine analogue and NO synthase inhibitor, NG-monomethyl-L-arginine monoacetate (MLA), could significantly suppress the ability of protective clones to inhibit MoPn in epithelial cells. The results suggested that the IFN-gamma-inducible NO synthease pathway is important for chlamydial control in mice. Furthermore, IFN-gamma could stimulate infected murine epithelial cells (line TM3) to secrete NO, resulting in inhibition of MoPn growth. However, the degree of MoPn inhibition obtained with IFN-gamma alone was less than that observed when T cells were co-cultured with infected epithelial cells. T-cell-derived NO could partly explain the enhanced chlamydial inhibition when T cells were co-cultured with infected epithelial cells. These results are consistent with the hypothesis that, besides T-cell-derived IFN-gamma, other factors associated with lymphoepithelial interactions are likely to contribute an important role in chlamydial control by T cells in mice.