Essential role of MHC II in the antitubercular efficacy of pyrazinamide.

Antibacterial drug mechanisms have traditionally been examined through a drug-pathogen lens, with limited attention to host influences on drug activity. However, growing evidence suggests that the host environment is crucial for antibacterial efficacy. Pyrazinamide (PZA), a key component of modern tuberculosis therapy, exemplifies this complexity, exhibiting potent in vivo activity despite its inability to reduce Mycobacterium tuberculosis viability in standard in vitro culture. Here, using macrophage and murine infection models, we identify a critical role for CD4+ T cell-dependent cell-mediated immunity in PZA's antitubercular action. Using MHC class II knockout mice, we demonstrate that CD4 T-cell help is essential for PZA efficacy. While interferon gamma (IFN-γ) is required for PZA-mediated clearance of M. tuberculosis at extrapulmonary sites, bacterial reduction in the lungs occurs, independent of IFN-γ signaling. We show that PZA leverages cell-mediated immunity in part through activation of the oxidative burst. Our findings underscore the need to incorporate host factors into antibacterial drug evaluation and highlight potential avenues for host-directed therapies and adjunctive antibiotics in first- and second-line tuberculosis treatment.