Diverse Clinical Isolates of Mycobacterium tuberculosis Develop Macrophage-Induced Rifampin Tolerance.

The Mycobacterium tuberculosis lineage 4 strains CDC1551 and H37Rv develop tolerance to multiple antibiotics upon macrophage residence. To determine whether macrophage-induced tolerance is a general feature of clinical M. tuberculosis isolates, we assessed macrophage-induced drug tolerance in strains from lineages 1-3, representing the other predominant M. tuberculosis strains responsible for tuberculosis globally. All 3 lineages developed isoniazid tolerance. While lineage 1, 3, and 4 strains developed rifampin tolerance, lineage 2 Beijing strains did not. Their failure to develop tolerance may be explained by their harboring of a loss-of-function mutation in the Rv1258c efflux pump that is linked to macrophage-induced rifampicin tolerance

Mycobacterial Acid Tolerance Enables Phagolysosomal Survival and Establishment of Tuberculous Infection In Vivo.

The blockade of phagolysosomal fusion is considered a critical mycobacterial strategy to survive in macrophages. However, viable mycobacteria have been observed in phagolysosomes during infection of cultured macrophages, and mycobacteria have the virulence determinant MarP, which confers acid resistance in vitro. Here we show in mice and zebrafish that innate macrophages overcome mycobacterial lysosomal avoidance strategies to rapidly deliver a substantial proportion of infecting bacteria to phagolysosomes. Exploiting the optical transparency of the zebrafish, we tracked the fates of individual mycobacteria delivered to phagosomes versus phagolysosomes and discovered that bacteria survive and grow in phagolysosomes, though growth is slower. MarP is required specifically for phagolysosomal survival, making it an important determinant for the establishment of mycobacterial infection in their hosts. Our work suggests that if pathogenic mycobacteria fail to prevent lysosomal trafficking, they tolerate the resulting acidic environment of the phagolysosome to establish infection.National Institutes of Health (Grant IDs: R37AI054503, R01 AI076327, 5T32HD007233, 5F30HL110455), Wellcome Trust, National Institute of Health Research Cambridge Biomedical Research CentreThis is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.chom.2016.07.00

Immune Vulnerability of Infants to Tuberculosis

One of the challenges faced by the infant immune system is learning to distinguish the myriad of foreign but nonthreatening antigens encountered from those expressed by true pathogens. This balance is reflected in the diminished production of proinflammatory cytokines by both innate and adaptive immune cells in the infant. A downside of this bias is that several factors critical for controlling Mycobacterium tuberculosis infection are significantly restricted in infants, including TNF, IL-1, and IL-12. Furthermore, infant T cells are inherently less capable of differentiating into IFN-γ-producing T cells. As a result, infected infants are 5–10 times more likely than adults to develop active tuberculosis (TB) and have higher rates of severe disseminated disease, including miliary TB and meningitis. Infant TB is a fundamentally different disease than TB in immune competent adults. Immunotherapeutics, therefore, should be specifically evaluated in infants before they are routinely employed to treat TB in this age group. Modalities aimed at reducing inflammation, which may be beneficial for adjunctive therapy of some forms of TB in older children and adults, may be of no benefit or even harmful in infants who manifest much less inflammatory disease

Assessing vaccine-mediated protection in an ultra-low dose Mycobacterium tuberculosis murine model.

Despite widespread immunization with Bacille-Calmette-Guérin (BCG), the only currently licensed tuberculosis (TB) vaccine, TB remains a leading cause of mortality globally. There are many TB vaccine candidates in the developmental pipeline, but the lack of a robust animal model to assess vaccine efficacy has hindered our ability to prioritize candidates for human clinical trials. Here we use a murine ultra-low dose (ULD) Mycobacterium tuberculosis (Mtb) challenge model to assess protection conferred by BCG vaccination. We show that BCG confers a reduction in lung bacterial burdens that is more durable than that observed after conventional dose challenge, curbs Mtb dissemination to the contralateral lung, and, in a small percentage of mice, prevents detectable infection. These findings are consistent with the ability of human BCG vaccination to mediate protection, particularly against disseminated disease, in specific human populations and clinical settings. Overall, our findings demonstrate that the ultra-low dose Mtb infection model can measure distinct parameters of immune protection that cannot be assessed in conventional dose murine infection models and could provide an improved platform for TB vaccine testing

Contained Mycobacterium tuberculosis infection induces concomitant and heterologous protection

Progress in tuberculosis vaccine development is hampered by an incomplete understanding of the immune mechanisms that protect against infection with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. Although the M72/ASOE1 trial yielded encouraging results (54% efficacy in subjects with prior exposure to Mtb), a highly effective vaccine against adult tuberculosis remains elusive. We show that in a mouse model, establishment of a contained and persistent yet non-pathogenic infection with Mtb ("contained Mtb infection", CMTB) rapidly and durably reduces tuberculosis disease burden after re-exposure through aerosol challenge. Protection is associated with elevated activation of alveolar macrophages, the first cells that respond to inhaled Mtb, and accelerated recruitment of Mtb-specific T cells to the lung parenchyma. Systems approaches, as well as ex vivo functional assays and in vivo infection experiments, demonstrate that CMTB reconfigures tissue resident alveolar macrophages via low grade interferon-γ exposure. These studies demonstrate that under certain circumstances, the continuous interaction of the immune system with Mtb is beneficial to the host by maintaining elevated innate immune responses