Essential Role of MHC II in the Antitubercular Efficacy of Pyrazinamide

Abstract

Antibacterial drug mechanisms have traditionally been examined through a drug-pathogen lens, often overlooking the host's 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 PZA's 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-γ is required for PZA-mediated clearance of M. tuberculosis at extrapulmonary sites, bacterial reduction in the lungs occurs independently of IFN-γ 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.

Keywords: CD4 T cells; MHC II; Mycobacterium tuberculosis; Pyrazinamide; interferon-gamma; oxidative burst.

Figure 1.. PZA activity is dependent on the oxidative burst.

PZA bactericidal activity in Mtb strain H37Rv infected (A) C57BL/6J, (B) ifngR1 KO, (C) C57BL/6JN, and (D) p47^phox KO BMDMs. Infected resting and IFN-γ activated BMDMs were untreated or treated with PZA (200 μg/mL or 400 μg/mL). Cultures were plated for bacterial enumeration at indicated timepoints. Statistical significance was calculated based on multiple comparisons with 2-way ANOVA with Bonferoni correction. **P<0.005.

Figure 2.. PZA failure in ifngR1 KO and MCH II KO mice.

Mtb strain H37Rv total bacterial burden in lungs, livers, and spleens of C57BL/6J, ifngR1 KO, and MHC II KO mice. All mice were infected with low-dose aerosol Mtb and the infection was allowed to progress for 3-weeks in order for cell-mediated immunity to initiate (pretreatment). Mice were subsequently treated daily for 5 days a week for 2 weeks with either vehicle control (sterile water), PZA (150 mg/kg), and IN (30 mg/kg). Upon euthanasia, organs were removed, homogenized, and plated for bacterial enumeration at indicated timepoints. Empty circles on the x-axis indicates animals for which no bacterial growth was detected. Statistical significance was calculated based on paired two-tailed t-tests and p values were adjusted for multiple comparisons. *P<0.05, ***P<0.0005, ns not significant.