B cells in the regulation of lung granulomatous inflammation in TB

A hallmark of the host response to Mycobacterium tuberculosis (Mtb) is the development of the inflammatory granuloma, which plays an important role in controlling Mtb while also capable of inducing tissue-damaging lung pathology in chronic tuberculosis (TB), causing necrosis and cavitation. Cavitary lesions, when in communication with the respiratory tree, attain ambient O2 levels to promote bacillary growth to high concentrations, thereby facilitating Mtb transmission. Thus, this process poses a significant obstacle to TB control. Further, the exacerbated pathology can result in permanently compromised lung functions, even after curative therapy. The mechanisms that regulate the development of tissue-damaging immunopathology in chronic TB are incompletely defined. In chronic TB, B cells form in the lungs prominent aggregates that are an integral part of ectopic germinal centers, cellular structures associated with chronic inflammation that can regulate local immune responses. Using B cell-deficient mouse models, we have shown that B cells drive lung inflammation in chronic TB. Compared to B cell-deficient mice, B cell-adequate animals display increased lung infiltration that is associated with enhanced CD4+ T cell expansion and an augmented level of pro-inflammatory interferon (IFN)-g-producing CD4+ T cells; concomitant with diminished lung expression of the anti-inflammatory IL-10. The B cell-deficient mouse CD4+ T cell phenotypes can be reversed by IL-10 signaling blockade. The CD4+ T cell data suggest that in chronic TB, B cells may drive CD4+ T cell expansion and the pro-inflammatory Th1 response, possibly by presenting antigens (Ags) to CD4+ T cells, that latter an understudied B cell function. The IL-10 results suggest that B cells can restrict lung IL-10 expression in chronic TB, and that IL-10 can regulate lung inflammation, possibly by modulating the functions of CD4+ T cells and Ag presenting cells. Our results also suggest a role for cytokines in modulating lung inflammation in chronic TB. Of note, we have shown that necrotic and cavitary lesions in the lungs of humans with chronic TB are decorated with conspicuous B cell aggregates at their periphery, suggesting that B cells may regulate tissue-damaging pathology. This proposal seeks to i) elucidate the mechanisms by which B cells regulate lung inflammation in chronic TB in mice, particularly those operative in the B cell/IL-10/Th1 axis; and ii) characterize the lesion-associated B cell aggregates in the lungs of humans with chronic TB. We will accomplish this by leveraging a variety of knock-out and transgenic mouse strains and the expansive repository of human TB tissues available at the University of Alabama at Birmingham, together with state-of-the-art technologies including multiplex immunofluorescence analysis, gene expression profiling via RNAscope, single-cell RNA-sequencing, and spatial transcriptomics. We believe the results generated by the proposed studies can illuminate how B cells regulate lung inflammation in chronic TB and point toward interventional strategies capable of mitigating TB transmission and the development of undesirable pulmonary function sequalae of chronic TB.