Immunotherapy With 5, 15-DPP Mediates Macrophage M1 Polarization and Modulates Subsequent Mycobacterium tuberculosis Infectivity in rBCG30 Immunized Mice

Heparin-Binding Hemagglutinin of Mycobacterium tuberculosis Inhibits Autophagy via Toll-like Receptor 4 and Drives M2 Polarization in Macrophages

BACKGROUND

Tuberculosis (TB), predominantly caused by Mycobacterium tuberculosis (MTB) infection, remains a prominent global health challenge. Macrophages are the frontline defense against MTB, relying on autophagy for intracellular bacterial clearance. However, MTB can combat and evade autophagy, and it influences macrophage polarization, facilitating immune evasion and promoting infection. We previously found that heparin-binding hemagglutinin (HBHA) inhibits autophagy in A549 cells; however, its role in macrophage autophagy and polarization remains unclear.

METHODS

Bacterial cultures, cell cultures, Western blotting, immunofluorescence, macrophage infection assays, siRNA knockdown, and enzyme-linked immunosorbent assay were used to investigate HBHA's impact on macrophages and its relevance in Mycobacterium infection.

RESULTS

HBHA inhibited macrophage autophagy. Expression of recombinant HBHA in Mycobacterium smegmatis (rMS-HBHA) inhibited autophagy, promoting bacterial survival within macrophages. Conversely, HBHA knockout in the Mycobacterium bovis bacillus Calmette-Guérin (BCG) mutant (BCG-ΔHBHA) activated autophagy and reduced bacterial survival. Mechanistic investigations revealed that HBHA may inhibit macrophage autophagy through the Toll-like receptor 4-dependent PI3K-AKT-mTOR signaling pathway. Furthermore, HBHA induced macrophage M2 polarization.

CONCLUSIONS

Mycobacterium may exploit HBHA to suppress the antimicrobial immune response in macrophages, facilitating intracellular survival and immune evasion through autophagy inhibition and M2 polarization induction. Our findings may help identify novel therapeutic targets and develop more effective treatments against MTB infection.

IL-10 Overexpression After BCG Vaccination Does Not Impair Control of Mycobacterium tuberculosis Infection

Control of tuberculosis depends on the rapid expression of protective CD4+ T-cell responses in the Mycobacterium tuberculosis (Mtb)-infected lungs. We have recently shown that the immunomodulatory cytokine IL-10 acts intrinsically in CD4+ T cells and impairs their parenchymal migratory capacity, thereby preventing control of Mtb infection. Herein, we show that IL-10 overexpression does not impact the protection conferred by the established memory CD4+ T-cell response, as BCG-vaccinated mice overexpressing IL-10 only during Mtb infection display an accelerated, BCG-induced, Ag85b-specific CD4+ T-cell response and control Mtb infection. However, IL-10 inhibits the migration of recently activated ESAT-6-specific CD4+ T cells into the lung parenchyma and impairs the development of ectopic lymphoid structures associated with reduced expression of the chemokine receptors CXCR5 and CCR7. Together, our data support a role for BCG vaccination in preventing the immunosuppressive effects of IL-10 in the fast progression of Mtb infection and may provide valuable insights on the mechanisms contributing to the variable efficacy of BCG vaccination.

Macrophage: A Cell With Many Faces and Functions in Tuberculosis

Mycobacterium tuberculosis (Mtb) is the causative agent of human tuberculosis (TB) which primarily infects the macrophages. Nearly a quarter of the world's population is infected latently by Mtb. Only around 5%-10% of those infected develop active TB disease, particularly during suppressed host immune conditions or comorbidity such as HIV, hinting toward the heterogeneity of Mtb infection. The aerosolized Mtb first reaches the lungs, and the resident alveolar macrophages (AMs) are among the first cells to encounter the Mtb infection. Evidence suggests that early clearance of Mtb infection is associated with robust innate immune responses in resident macrophages. In addition to lung-resident macrophage subsets, the recruited monocytes and monocyte-derived macrophages (MDMs) have been suggested to have a protective role during Mtb infection. Mtb, by virtue of its unique cell surface lipids and secreted protein effectors, can evade killing by the innate immune cells and preferentially establish a niche within the AMs. Continuous efforts to delineate the determinants of host defense mechanisms have brought to the center stage the crucial role of macrophage phenotypical variations for functional adaptations in TB. The morphological and functional heterogeneity and plasticity of the macrophages aid in confining the dissemination of Mtb. However, during a suppressed or hyperactivated immune state, the Mtb virulence factors can affect macrophage homeostasis which may skew to favor pathogen growth, causing active TB. This mini-review is aimed at summarizing the interplay of Mtb pathomechanisms in the macrophages and the implications of macrophage heterogeneity and plasticity during Mtb infection.