CpsA mediates infection of recruited lung myeloid cells by Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) possesses an arsenal of virulence factors to evade host immunity. Previously, we showed that the Mtb protein CpsA, which protects Mtb against the host NADPH oxidase, is required in mice during the first 3 weeks of infection but is thereafter dispensable for full virulence. Using flow cytometry, we find that ΔcpsA Mtb is retained in alveolar macrophages, impaired in recruiting and disseminating into monocyte-derived cells, and more likely to be localized in airway cells than wild-type Mtb. The lungs of ΔcpsA-infected mice also have markedly fewer antigen-specific T cells, indicating a delay in adaptive immunity. Thus, we conclude that CpsA promotes dissemination of Mtb from alveolar macrophages and the airways and generation of an adaptive immune response. Our studies of ΔcpsA Mtb show that a more effective innate immune response against Mtb can be undermined by a corresponding delay in the adaptive immune response.

Immune evasion and provocation by Mycobacterium tuberculosis.

Mycobacterium tuberculosis, the causative agent of tuberculosis, has infected humans for millennia. M. tuberculosis is well adapted to establish infection, persist in the face of the host immune response and be transmitted to uninfected individuals. Its ability to complete this infection cycle depends on it both evading and taking advantage of host immune responses. The outcome of M. tuberculosis infection is often a state of equilibrium characterized by immunological control and bacterial persistence. Recent data have highlighted the diverse cell populations that respond to M. tuberculosis infection and the dynamic changes in the cellular and intracellular niches of M. tuberculosis during the course of infection. M. tuberculosis possesses an arsenal of protein and lipid effectors that influence macrophage functions and inflammatory responses; however, our understanding of the role that specific bacterial virulence factors play in the context of diverse cellular reservoirs and distinct infection stages is limited. In this Review, we discuss immune evasion and provocation by M. tuberculosis during its infection cycle and describe how a more detailed molecular understanding is crucial to enable the development of novel host-directed therapies, disease biomarkers and effective vaccines.

Mycobacterium tuberculosis is protected from NADPH oxidase and LC3-associated phagocytosis by the LCP protein CpsA.

Mycobacterium tuberculosis' success as a pathogen comes from its ability to evade degradation by macrophages. Normally macrophages clear microorganisms that activate pathogen-recognition receptors (PRRs) through a lysosomal-trafficking pathway called "LC3-associated phagocytosis" (LAP). Although Mtuberculosis activates numerous PRRs, for reasons that are poorly understood LAP does not substantially contribute to Mtuberculosis control. LAP depends upon reactive oxygen species (ROS) generated by NADPH oxidase, but Mtuberculosis fails to generate a robust oxidative response. Here, we show that CpsA, a LytR-CpsA-Psr (LCP) domain-containing protein, is required for Mtuberculosis to evade killing by NADPH oxidase and LAP. Unlike phagosomes containing wild-type bacilli, phagosomes containing the ΔcpsA mutant recruited NADPH oxidase, produced ROS, associated with LC3, and matured into antibacterial lysosomes. Moreover, CpsA was sufficient to impair NADPH oxidase recruitment to fungal particles that are normally cleared by LAP. Intracellular survival of the ΔcpsA mutant was largely restored in macrophages missing LAP components (Nox2, Rubicon, Beclin, Atg5, Atg7, or Atg16L1) but not in macrophages defective in a related, canonical autophagy pathway (Atg14, Ulk1, or cGAS). The ΔcpsA mutant was highly impaired in vivo, and its growth was partially restored in mice deficient in NADPH oxidase, Atg5, or Atg7, demonstrating that CpsA makes a significant contribution to the resistance of Mtuberculosis to NADPH oxidase and LC3 trafficking in vivo. Overall, our findings reveal an essential role of CpsA in innate immune evasion and suggest that LCP proteins have functions beyond their previously known role in cell-wall metabolism.