Gadwa, J. | bioRxiv Science

bioRxiv2022

Phagosomal RNA sensing through TLR8 controls susceptibility to tuberculosis

Genetic determinants of susceptibility to Mycobacterium tuberculosis (Mtb) are poorly understood but could provide insights into critical pathways involved in infection, informing host-directed therapies and enabling risk stratification at individual and population levels. Through a genome-wide forward genetic screen, we identify the Toll-like Receptor 8 (TLR8), as a key regulator of intracellular killing of Mtb. Pharmacological TLR8 activation enhances killing of phylogenetically diverse clinical isolates of drug-susceptible and multidrug-resistant Mtb by macrophages and during in vivo infection in mice. TLR8 is activated by phagosomal mycobacterial RNA released by extracellular membrane vesicles, and enhances xenophagy-dependent Mtb killing. We find that the TLR8 variant, M1V, common in far eastern populations, enhances intracellular killing of Mtb through preferential signal-dependent trafficking to phagosomes. TLR8 signalling may therefore both regulate susceptibility to tuberculosis and provide novel drug targets. Single sentence summaryRNA released from Mycobacterium tuberculosis in the macrophage phagosome is sensed by the pattern recognition receptor TLR8 controlling host susceptibility to tuberculosis and revealing a druggable pathway for host-directed therapy.

immunology↗

bioRxiv2022

Ex vivo and in vivo evidence that cigarette smoke-exposed T regulatory cells impair host immunity against Mycobacterium tuberculosis

A strong epidemiologic link exists between exposure to cigarette smoke (CS) and increased susceptibility to tuberculosis (TB). In vitro macrophage and in vivo murine studies showed that CS and nicotine impair host-protective immune cells against Mycobacterium tuberculosis (MTB) infection. However, little is known about how CS may affect immunosuppressive cells in the context of MTB infection. Thus, we investigated whether CS-exposed T regulatory cells (Tregs) could exacerbate MTB infection in co-culture with human macrophages and in the adoptive transfer of Tregs from air- and CS-exposed mice. We found that exposure of primary human Tregs to CS extract impaired the ability of human monocyte-derived macrophages to control an MTB infection by inhibiting phagosome-lysosome fusion and autophagosome formation. Neutralization of CTLA-4 on the CS extract-exposed Tregs abrogated the impaired control of MTB infection in macrophage and Treg co-cultures. In Foxp3+GFP+DTR+ (Thy1.2) mice depleted of endogenous Tregs, adoptive transfer of Tregs from donor CS-exposed B6.PL(Thy1.1) mice with subsequent MTB infection of the recipient Thy1.2 mice resulted in a greater burden of MTB in the lungs and spleens than those that received Tregs from airexposed mice. Mice that received Tregs from CS-exposed mice and then infected with MTB had modest but significantly reduced numbers of interleukin-12-positive dendritic cells and interferon-gamma-positive CD4+ T cells in the lungs and increased number of programmed cell death protein-1 positive CD4+ T cells in both the lungs and spleens.

immunology↗