Sabine Jörg

Human tuberculous granulomas induce peripheral lymphoid follicle-like structures to orchestrate local host defence in the lung

The human tuberculous granuloma provides the morphological basis for local immune processes central to the outcome of tuberculosis. Because of the scarcity of information in human patients, the aim of the present study was to gain insights into the functional and structural properties of infiltrated tissue. To this end, the mycobacterial load in lesions and dissemination to different tissue locations were investigated, as well as distribution, biological functions, and interactions of host immune cells. Analysis of early granuloma formation in formerly healthy lung tissue revealed a spatio‐temporal sequence of cellular infiltration to sites of mycobacterial infection. A general structure of the developing granuloma was identified, comprising an inner cell layer with few CD8+ cells surrounding the necrotic centre and an outer area of lymphocyte infiltration harbouring mycobacteria‐containing antigen‐presenting cells as well as CD4+, CD8+, and B cells in active follicle‐like centres resembling secondary lymphoid organs. It is concluded that the follicular structures in the peripheral rim of granulomas serve as a morphological substrate for the orchestration of the enduring host response in pulmonary tuberculosis. Copyright

Mutation in the Transcriptional Regulator PhoP Contributes to Avirulence of Mycobacterium tuberculosis H37Ra Strain

Attenuated strains of mycobacteria can be exploited to determine genes essential for their pathogenesis and persistence. To this goal, we sequenced the genome of H37Ra, an attenuated variant of Mycobacterium tuberculosis H37Rv strain. Comparison with H37Rv revealed three unique coding region polymorphisms. One polymorphism was located in the DNA-binding domain of the transcriptional regulator PhoP, causing the proteins diminished DNA-binding capacity. Temporal gene expression profiles showed that several genes with reduced expression in H37Ra were also repressed in an H37Rv phoP knockout strain. At later time points, genes of the dormancy regulon, typically expressed in a state of nonreplicating persistence, were upregulated in H37Ra. Complementation of H37Ra with H37Rv phoP partially restored its persistence in a murine macrophage infection model. Our approach demonstrates the feasibility of identifying minute but distinct differences between isogenic strains and illustrates the consequences of single point mutations on the survival stratagem of M. tuberculosis.

MicroRNA-223 controls susceptibility to tuberculosis by regulating lung neutrophil recruitment

The molecular mechanisms that control innate immune cell trafficking during chronic infection and inflammation, such as in tuberculosis (TB), are incompletely understood. During active TB, myeloid cells infiltrate the lung and sustain local inflammation. While the chemoattractants that orchestrate these processes are increasingly recognized, the posttranscriptional events that dictate their availability are unclear. We identified microRNA-223 (miR-223) as an upregulated small noncoding RNA in blood and lung parenchyma of TB patients and during murine TB. Deletion of miR-223 rendered TB-resistant mice highly susceptible to acute lung infection. The lethality of miR-223(–/–) mice was apparently not due to defects in antimycobacterial T cell responses. Exacerbated TB in miR-223(–/–) animals could be partially reversed by neutralization of CXCL2, CCL3, and IL-6, by mAb depletion of neutrophils, and by genetic deletion of Cxcr2. We found that miR-223 controlled lung recruitment of myeloid cells, and consequently, neutrophil-driven lethal inflammation. We conclude that miR-223 directly targets the chemoattractants CXCL2, CCL3, and IL-6 in myeloid cells. Our study not only reveals an essential role for a single miRNA in TB, it also identifies new targets for, and assigns biological functions to, miR-223. By regulating leukocyte chemotaxis via chemoattractants, miR-223 is critical for the control of TB and potentially other chronic inflammatory diseases.

Differential organization of the local immune response in patients with active cavitary tuberculosis or with nonprogressive tuberculoma.

BACKGROUND In 90% of all cases, Mycobacterium tuberculosis infection results in latency rather than active disease, with the pathogen being contained within granulomatous lesions at the site of primary infection. Failure of this containment leads to reactivation of postprimary tuberculosis (TB). The regional immune processes that sustain the delicate balance with persistent M. tuberculosis, however, remain unclear. METHODS We compared activation statuses, biological functions, and interactions of host immune cells in human nonprogressive tuberculoma and active cavitary tuberculous lung tissue. RESULTS Dissection of early granuloma formations revealed differential cellular distribution and activation statuses of distinct cell types in different regions relative to the central caseotic caverna or the tuberculoma in tuberculous lung tissue. In patients with tuberculoma with latent infection, distant parts of lung tissue exhibited strong vascularization and profound proliferative activity, indicating that continuous immune defense is required for mycobacterial containment, which is absent in cavitary tuberculous lung lesions. CONCLUSIONS We conclude that differential regulation of the local immune response is crucial for the containment of M. tuberculosis and that a continuous antigen-specific cross talk between the host immune system and M. tuberculosis is ensured during latency. This activation requires sufficient supply of nutrients and well-coordinated structural organization, both of which are lost during reactivation of TB.

Activation of the NLRP3 inflammasome by Mycobacterium tuberculosis is uncoupled from susceptibility to active tuberculosis

As a hallmark of tuberculosis (TB), Mycobacterium tuberculosis (MTB) induces granulomatous lung lesions and systemic inflammatory responses during active disease. Molecular regulation of inflammation is associated with inflammasome assembly. We determined the extent to which MTB triggers inflammasome activation and how this impacts on the severity of TB in a mouse model. MTB stimulated release of mature IL‐1β in macrophages while attenuated M. bovis BCG failed to do so. Tubercle bacilli specifically activated the NLRP3 inflammasome and this propensity was strictly controlled by the virulence‐associated RD1 locus of MTB. However, Nlrp3‐deficient mice controlled pulmonary TB, a feature correlated with NLRP3‐independent production of IL‐1β in infected lungs. Our studies demonstrate that MTB activates the NLRP3 inflammasome in macrophages in an ESX‐1‐dependent manner. However, during TB, MTB promotes NLRP3‐ and caspase‐1‐independent IL‐1β release in myeloid cells recruited to lung parenchyma and thus overcomes NLRP3 deficiency in vivo in experimental models.

Type I IFN signaling triggers immunopathology in tuberculosis-susceptible mice by modulating lung phagocyte dynamics.

General interest in the biological functions of IFN type I in Mycobacterium tuberculosis (Mtb) infection increased after the recent identification of a distinct IFN gene expression signature in tuberculosis (TB) patients. Here, we demonstrate that TB‐susceptible mice lacking the receptor for IFN I (IFNAR1) were protected from death upon aerogenic infection with Mtb. Using this experimental model to mimic primary progressive pulmonary TB, we dissected the immune processes affected by IFN I. IFNAR1 signaling did not affect T‐cell responses, but markedly altered migration of inflammatory monocytes and neutrophils to the lung. This process was orchestrated by IFNAR1 expressed on both immune and tissue‐resident radioresistant cells. IFNAR1‐driven TB susceptibility was initiated by augmented Mtb replication and in situ death events, along with CXCL5/CXCL1‐driven accumulation of neutrophils in alveoli, followed by the discrete compartmentalization of Mtb in lung phagocytes. Early depletion of neutrophils rescued TB‐susceptible mice to levels observed in mice lacking IFNAR1. We conclude that IFN I alters early innate events at the site of Mtb invasion leading to fatal immunopathology. These data furnish a mechanistic explanation for the detrimental role of IFN I in pulmonary TB and form a basis for understanding the complex roles of IFN I in chronic inflammation.

Lung-Residing Myeloid-derived Suppressors Display Dual Functionality in Murine Pulmonary Tuberculosis

RATIONALE Myeloid cells encompass distinct populations with unique functions during homeostasis and disease. Recently, a novel subset of innate cells, myeloid-derived suppressor cells (MDSCs), has been described in cancer, which suppresses T-cell responses and fosters disease progression. The role of MDSCs in infection is insufficiently addressed. OBJECTIVES To examine the presence and function of MDSCs during experimental pulmonary tuberculosis (TB) and further understand the immunologic consequences of direct interactions between MDSCs and lung bacterial pathogens. METHODS Using cell-based approaches and experimental mouse models for pulmonary TB we characterized MDSCs as novel myeloid populations directly interacting with Mycobacterium tuberculosis (Mtb). MEASUREMENTS AND MAIN RESULTS MDSCs readily phagocytosed Mtb, and released proinflammatory (IL-6, IL-1α) and immunomodulatory (IL-10) cytokines while retaining their suppressive capacity. MDSCs were identified at the site of infection in the lung in disease-resistant and -susceptible mice during pulmonary TB. Excessive MDSC accumulation in lungs correlated with elevated surface expression of IL-4Rα and heightened TB lethality, whereas targeted depletion of MDSCs ameliorated disease. CONCLUSIONS Our data reveal that MDSCs provide a niche for pathogen survival and tailor immunity in TB. These findings suggest MDSCs as amenable targets for host-directed therapies and emphasize them as cellular-immune regulators during chronic inflammatory conditions, including chronic infections and microbial complications of neoplastic disorders.

Secondary lymphoid organs are dispensable for the development of T‐cell‐mediated immunity during tuberculosis

Tuberculosis causes 2 million deaths per year, yet in most cases the immune response successfully contains the infection and prevents disease outbreak. Induced lymphoid structures associated with pulmonary granuloma are observed during tuberculosis in both humans and mice and could orchestrate host defense. To investigate whether granuloma perform lymphoid functions, mice lacking secondary lymphoid organs (SLO) were infected with Mycobacterium tuberculosis (MTB). As in WT mice, granuloma developed, exponential growth of MTB was controlled, and antigen‐specific T‐cell responses including memory T cells were generated in the absence of SLO. Moreover, adoptively transferred T cells were primed locally in lungs in a granuloma‐dependent manner. T‐cell activation was delayed in the absence of SLO, but resulted in a normal development program including protective subsets and functional recall responses that protected mice against secondary MTB infection. Our data demonstrate that protective immune responses can be generated independently of SLO during MTB infection and implicate local pulmonary T‐cell priming as a mechanism contributing to host defense.

Impact of inducible co‐stimulatory molecule (ICOS) on T‐cell responses and protection against Mycobacterium tuberculosis infection

Even though Mycobacterium tuberculosis (Mtb) remains one of the top microbial killers, more than 90% of the 2 billion infected individuals never develop active tuberculosis (TB), indicating efficient immune control of infection in these individuals. Immune mechanisms promoting either control or reactivation of TB are incompletely understood. Kinetic analyses of T‐cell responses against Mtb in C57BL/6 mice revealed surface expression of inducible co‐stimulatory molecule (ICOS) on >30% of all CD4+ T cells, suggesting a pivotal role of this costimulatory molecule of the CD28 family in TB control. Surprisingly, Mtb‐infected ICOS−/− mice showed lower bacterial burden during the late chronic stage of infection as compared to WT controls. ICOS deficiency resulted in a reduced Mtb‐specific CD8+ T‐cell response during late‐stage infection. In contrast, the polyclonal CD4+ Th1 response against Mtb was increased, most likely caused by diminished numbers and frequencies of Tregs. Thus, by altering effector T‐cell populations differentially, ICOS signaling modulates TB control in the late stage of infection.