Rather, M. | Search bioRxiv

bioRxiv2025

Essential Role of MHC II in the Antitubercular Efficacy of Pyrazinamide

Antibacterial drug mechanisms have traditionally been examined through a drug-pathogen lens, often overlooking the hosts role in shaping 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 host cell-mediated immunity in PZAs antitubercular action. Through the use of MHC II knockout mice, we demonstrate that CD4 T cell help is essential for PZA efficacy. Notably, while IFN-{gamma} is required for PZA-mediated clearance of M. tuberculosis at extrapulmonary sites, bacterial reduction in the lungs occurs independently of IFN-{gamma} signaling. Additionally, 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.

microbiology↗

bioRxiv2024

Oxidative stress drives potent bactericidal activity of pyrazinamide against Mycobacterium tuberculosis

Pyrazinamide (PZA) is a critical component of tuberculosis first-line therapy due to its ability to kill both growing and non-replicating drug-tolerant populations of Mycobacterium tuberculosis within the host. Recent evidence indicates that PZA acts through disruption of coenzyme A synthesis under conditions that promote cellular stress. In contrast to its bactericidal action in vivo, PZA shows weak bacteriostatic activity against M. tuberculosis in axenic culture. While the basis for this striking difference between in vivo and in vitro PZA activity has yet to be resolved, recent studies have highlighted an important role for cell-mediated immunity in PZA efficacy. These observations suggest that host-derived antimicrobial activity may contribute to the bactericidal action of PZA within the host environment. In this study we show that the active form of PZA, pyrazinoic acid (POA), synergizes with the bactericidal activity of host-derived reactive oxygen species (ROS). We determined that POA can promote increased cellular oxidative damage and enhanced killing of M. tuberculosis. Further, we find that the thiol oxidant diamide is also able to potentiate PZA activity, implicating thiol oxidation as a key driver of PZA susceptibility. Using a macrophage infection model, we demonstrate the essentiality of interferon-{gamma} induced ROS production for PZA mediated clearance of M. tuberculosis. Based on these observations, we propose that the in vivo sterilizing activity of PZA can be mediated through its synergistic interaction with the host oxidative burst leading to collateral disruption of coenzyme A metabolism. These findings will enable discovery efforts to identify novel host- and microbe-directed approaches to bolster PZA efficacy.

microbiology↗