Reviewer #2 (Public review): Mast cells promote pathology and susceptibility in tuberculosis

In this useful study, the authors utilize published scRNA-seq data to highlight the potential importance of mast cells (MCs) in TB granulomas, presenting a solid comparative assessment of chymaseand tryptase-expressing MCs in the lungs of Mycobacterium tuberculosis-infected individuals and non-human primates.While the authors appropriately discussed the inconsistencies across models, adoptive transfer experiments in MC-deficient mice would substantially strengthen the causal link between MCs and TB outcomes, providing more direct functional validation of the proposed role of MCs in TB pathogenesis.Abstract Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (Mtb), infects approximately one-fourth of the world's population.We reported an increased accumulation of mast cells (MCs) in the lungs of macaques with active pulmonary TB (PTB), compared with those with latent TB infection (LTBI).MCs respond in vitro to Mtb exposure via degranulation and by inducing proinflammatory cytokines.In the current study, we demonstrate an increased production of chymase by MCs in granulomas of humans and macaques with PTB.Single-cell (sc) RNA sequencing analysis revealed distinct MC transcriptional programs between LTBI and PTB, with PTB-associated MCs enriched in interferon gamma, oxidative phosphorylation, and MYC signaling.In a mouse model, MC deficiency led to improved control of Mtb infection that coincided with reduced accumulation of lung myeloid cells and diminished lung inflammation at chronic stages of infection.Airway transfer of MCs into wild-type Mtb-infected mice showed increased neutrophils, decreased recruited macrophages, and elevated Mtb dissemination to the spleen.Together, these findings highlight MCs as active drivers of TB pathogenesis and potential targets for host-directed therapies for TB.