Epithelial cells, not macrophages, drive human TB iNOS response

Tuberculosis remains a leading infectious killer, and scientists have long focused on immune cells called macrophages as the frontline defenders against the bacteria that cause the disease. A key part of that defense in many laboratory models is the induction of an enzyme called iNOS, which makes nitric oxide and is thought to be driven by a signaling molecule called IFNγ. The work led by Björn Corleis set out to test a simple but important question: how relevant is IFNγ-induced iNOS activity in humans and other natural hosts of virulent mycobacterial species? To do that, the team compared how myeloid cells from humans and mice respond to infection and to IFNγ. They broadened the comparison by looking at monocytes from seven mammalian species, rather than relying on one animal model. The study combined laboratory infection experiments with several kinds of molecular and imaging analysis to map where iNOS is made during tuberculosis and whether IFNγ controls that production in the same way across species. The goal was to understand whether assumptions based on mouse models hold true for primates and humans.

To tackle these questions the researchers used a mix of genomic, functional, and imaging tools. They applied bulk RNA sequencing to measure gene expression changes in infected myeloid cells across species and performed functional infection assays alongside nitric oxide measurements to test activity. They extended these analyses to monocytes from seven mammalian species and reanalyzed publicly available single-cell RNA-sequencing datasets. For tissue-level localization they used spatial proteomic imaging of tuberculous granulomas and multiplexed ion beam imaging. Across these approaches the team found a striking pattern: IFNγ signaling was uncoupled from iNOS induction in primate myeloid cells. In other words, primate macrophages did not turn on iNOS in response to IFNγ the way mouse macrophages do. Instead, multiplexed ion beam imaging localized iNOS protein to epithelial compartments adjacent to granulomatous lesions, indicating that epithelial cells are a dominant source of iNOS in human tuberculosis.

These findings change how we should think about immune responses in human tuberculosis. If IFNγ does not reliably induce iNOS in primate myeloid cells, then models that center on murine macrophage responses may miss important features of human disease. The study challenges murine macrophage-centric paradigms and calls into question IFNγ-based correlates used in TB vaccine development. It also highlights epithelial compartments—cells that line airways and tissue—as major contributors of iNOS in human tuberculosis, shifting attention away from macrophages alone. For researchers and clinicians, this means re-evaluating how laboratory and animal data are translated into human treatments and vaccine strategies, and considering epithelial immune responses as central to the pathophysiology of tuberculosis and other pneumonias.