Mutations in the btk gene encoding Bruton’s tyrosine kinase cause X-linked immune deficiency, with impaired B lymphocyte function as the major phenotype. Earlier, we demonstrated that CBA/N-xid mice, unlike the wild-type CBA mice, were not protected by bacillus Calmette-Guérin (BCG) vaccination against tuberculosis infection. Because IFN-γ–producing T cells and activated macrophages are key elements of antituberculosis protection, it remained unclear how the mutation predominantly affecting B cell functions interferes with responses along the T cell–macrophage axis. In this study, we show that B cell deficiency leads to an abnormally rapid neutrophil migration toward the site of external stimulus. Using adoptive cell transfers and B cell genetic knockout, we demonstrate a previously unappreciated capacity of B cells to downregulate neutrophil motility. In our system, an advanced capture of BCG by neutrophils instead of macrophages leads to a significant decrease in numbers of IFN-γ–producing T cells and impairs BCG performance in X-linked immune-deficient mice. The defect is readily compensated for by the in vivo neutrophil depletion.

The role of B cells migrating to the lung and forming follicles during tuberculosis (TB) inflammation is still the subject of debate. In addition to their antibody production and antigen-presenting functions, B cells secrete different cytokines and chemokines, thus participating in complex networks of innate and adaptive immunity. Importantly, lung B-cells produce high amounts of the pleiotropic gp130 cytokine IL-6. Its role during TB infection remains controversial, partly due to the fact that IL-6 is produced by different cell types. To investigate the impact of IL-6 produced by B cells on TB susceptibility and immune responses, we established a mouse strain with specific IL-6 deficiency in B cells (CD19cre-IL-6fl/fl, B-IL-6KO) on the B6 genetic background. Selective abrogation of IL-6 in B cells resulted in shortening the lifespan of TB-infected B-IL-6KO mice compare to the wild-type controls. We provide evidence that at the initial TB stages B cells serve as a critical source of IL-6. In the lung, the effect of IL-6 deficiency in B cells is associated rather with B and T cell functioning, than with macrophage polarization. TB-infected B-IL-6KO mice displayed diminished sizes of B cells themselves, CD4⁺IFN-γ⁺, Th17⁺, and CD4⁺CXCR5⁺follicular T cell populations. The pleiotropic effect of B-cell-derived IL-6 on T-cells demonstrated in our study bridges two major lymphocyte populations and sheds some light on B- and T-cells interactions during the stage of anti-TB response when the host switches on a plethora of acquired immune reactions.

During tuberculosis (TB) infection, B-lymphocytes migrate to the lungs and form B-cell follicles (BCFs) in the vicinity of TB granulomata. B-cell-lacking mice display enhanced susceptibility to TB infection, and early B-cell depletion in infected non-human primates alters T-lymphocyte cytokine responses and increases bacterial burdens in the lungs. However, the role of B cells during late TB stages remained unaddressed. Here, we demonstrate that B cells and BCFs persist up to weeks 25–45 post-challenge in the lungs of TB-resistant C57BL/6 (B6) mice. In hyper-susceptible I/St mice, B-cell content markedly drops between weeks 12–16 post-infection, paralleled by diffuse lung tissue inflammation and elevated gene expression levels for pro-inflammatory cytokines IL-1, IL-11, IL-17a, and TNF-α. To check whether B-cells/BCFs control TB infection at advanced stages, we specifically depleted B-cells from B6 mice by administrating anti-CD20 mAbs at week 16 post-infection. This resulted in more rapid cachexia, a shortened lifespan of the infected animals, an increase in (i) lung-infiltrating CD8⁺ T cells, (ii) IL-6 production by F4/80⁺ macrophages, (iii) expression levels of genes for neutrophil-attracting factors CXCL1 and IL-17, and tissue-damaging factors MMP8, MMP9, and S100A8. Taken together, our results suggest that lung B cells and BCFs are moderately protective against chronic TB infection.

Mycobacterium tuberculosis (Mtb) remains a major threat worldwide, although only a fraction of infected individuals develops tuberculosis (TB). TB susceptibility is shaped by multiple genetic factors, and we performed comparative immunological analysis of two mouse strains to uncover relevant mechanisms underlying susceptibility and resistance. C57BL/6 mice are relatively TB-resistant, whereas I/St mice are prone to develop severe TB, partly due to the MHC-II allelic variant that shapes suboptimal CD4⁺ T cell receptor repertoire. We investigated the repertoires of lung-infiltrating helper T cells and B cells at the progressed stage in both strains. We found that lung CD4⁺ T cell repertoires of infected C57BL/6 but not I/St mice contained convergent TCR clusters with functionally confirmed Mtb specificity. Transcriptomic analysis revealed a more prominent Th1 signature in C57BL/6, and expression of pro-inflammatory IL-16 in I/St lung-infiltrating helper T cells. The two strains also showed distinct Th2 signatures. Furthermore, the humoral response of I/St mice was delayed, less focused, and dominated by IgG/IgM isotypes, whereas C57BL/6 mice generated more Mtb antigen-focused IgA response. We conclude that the inability of I/St mice to produce a timely and efficient anti-Mtb adaptive immune responses arises from a suboptimal helper T cell landscape that also impacts the humoral response, leading to diffuse inflammation and severe disease.