Elevated IL-10 has been implicated in reactivation tuberculosis (TB). Since macrophages rather than T cells were reported to be the major source of IL-10 in TB, we analyzed the consequences of a macrophage-specific overexpression of IL-10 in transgenic mice (macIL-10-transgenic) after aerosol infection with Mycobacterium tuberculosis (Mtb). MacIL-10 transgenic mice were more susceptible to chronic Mtb infection than nontransgenic littermates, exhibiting higher bacterial loads in the lung after 12 wk of infection and dying significantly earlier than controls. The differentiation, recruitment, and activation of Th1 cells as well as the induction of IFN-γ-dependent effector genes against Mtb were not affected by macrophage-derived IL-10. However, microarray analysis of pulmonary gene expression revealed patterns characteristic of alternative macrophage activation that were overrepresented in Mtb-infected macIL-10 transgenic mice. Importantly, arginase-1 gene expression and activity were strikingly enhanced in transgenic mice accompanied by a reduced production of reactive nitrogen intermediates. Moreover, IL-10-dependent arginase-1 induction diminished antimycobacterial effector mechanisms in macrophages. Taken together, macrophage-derived IL-10 triggers aspects of alternative macrophage activation and promotes Mtb recrudescence independent of overt effects on anti-TB T cell immunity.

Human tuberculosis (TB) is a leading global health threat and still constitutes a major medical challenge. However, mechanisms governing tissue pathology during post-primary TB remain elusive, partly because genetically or immunologically tractable animal models are lacking. In human TB, the demonstration of a large relative increase in interleukin (IL)-4 and IL-13 expression, which correlates with lung damage, indicates that a subversive T helper (TH)2 component in the response to Mycobacterium tuberculosis (Mtb) may undermine protective immunity and contribute to reactivation and tissue pathology. Up to now, there has been no clear evidence regarding whether IL-4/IL-13-IL-4 receptor-α (Rα)-mediated mechanisms may in fact cause reactivation and pathology. Unfortunately, the virtual absence of centrally necrotizing granulomas in experimental murine TB is associated with a poor induction of a TH2 immune response. We therefore hypothesize that, in mice, an increased production of IL-13 may lead to a pathology similar to human post-primary TB. In our study, aerosol Mtb infection of IL-13-over-expressing mice in fact resulted in pulmonary centrally necrotizing granulomas with multinucleated giant cells, a hypoxic rim and a perinecrotic collagen capsule, with an adjacent zone of lipid-rich, acid-fast bacilli-containing foamy macrophages, thus strongly resembling the pathology in human post-primary TB. Granuloma necrosis (GN) in Mtb-infected IL-13-over-expressing mice was associated with the induction of arginase-1-expressing macrophages. Indirect blockade of the endogenous arginase inhibitor l-hydroxyarginine in Mtb-infected wild-type mice resulted in a strong arginase expression and precipitated a similar pathology of GN. Together, we here introduce an experimental TB model that displays many features of centrally necrotizing granulomas in human post-primary TB and demonstrate that IL-13/IL-4Rα-dependent mechanisms leading to arginase-1 expression are involved in TB-associated tissue pathology. © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Immunity to Mycobacterium tuberculosis infection is critically dependent on the timely priming of T effector lymphocytes and their efficient recruitment to the site of mycobacterial implantation in the lung. E-, P-, and L-selectin counterreceptors control lymphocyte homing to lymph nodes and leukocyte trafficking to peripheral sites of acute inflammation, their adhesive function depending on fucosylation by fucosyltransferases (FucT) IV and VII. To address the relative importance of differentially glycosylated selectin counterreceptors for priming of T cell effector functions in a model of mycobacteria-induced granulomatous pulmonary inflammation, we used aerosol-borne M. tuberculosis to infect FucT-IV−/−, FucT-VII−/−, FucT-IV−/−/FucT-VII−/−, or wild-type control mice. In lymph nodes, infected FucT-IV−/−/FucT-VII−/− and, to a lesser extent, FucT-VII−/− mice had severely reduced numbers of T cells and reduced Ag-specific effector responses. By contrast, recruitment of activated T cells into the lungs was similar in all four groups of mice during infection and expression of T cell, and macrophage effector functions were only delayed in lungs of FucT-IV−/−/FucT-VII−/− mice. Importantly, lungs from all groups expressed CXCL13, CCL21, and CCL19 and displayed organized follicular neolymphoid structures after infection with M. tuberculosis, which suggests that the lung served as a selectin ligand-independent priming site for immune responses to mycobacterial infection. All FucT-deficient strains were fully capable of restricting M. tuberculosis growth in infected organs until at least 150 days postinfection. Our observations indicate that leukocyte recruitment functions dictated by FucT-IV and FucT-VII-dependent selectin ligand activities are not critical for inducing or maintaining T cell effector responses at levels necessary to control pulmonary tuberculosis.

CD8 + T cells are involved in protection againstMycobacterium tuberculosis infection and represent a promising target for new vaccine strategies. Because IL-15 is important for the homeostasis of CD8 + T cells, we studied the immune response in IL-15-deficient mice during tuberculosis. In the absence of IL-15, CD8 + T cells failed to efficiently accumulate in draining lymph nodes and at the site of infection. The expression of antigen-specific effector functions, such as the production of interferon-c and cytotoxicity, were impaired in CD8 + T cells, but not CD4 + T cells, from IL-15-deficient mice. This defect was associated with an increased mortality of IL-15-deficient mice during the chronic phase of infection. The lectin-like stimulatory receptor natural killer group 2D (NKG2D) was up-regulated on CD8 + T cells only from wild-type mice, but not from IL-15-deficient mice. Mechanistically, blocking NKG2D function with an mAb inhibited M. tuberculosis-directed CD8 + T cell responses in vitro. We conclude that in addition to regulating the expansion of CD8 + T cells, IL-15 is also necessary for inducing effector mechanisms in CD8 + T cells that depend on NKG2D expression. Hence, our results implicate IL-15 and NKG2D as promising targets for modulating CD8 + T cellmediated protection against tuberculosis. IntroductionHuman tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is responsible for eight million new cases and two million deaths annually [1]. Improved vaccination strategies will need to target all mechanisms that contribute to restricting the growth of Mtb [2]. Although the cell-mediated immune response is known to be critical in host defense against infection with mycobacteria, the relative contribution of T cell subsets and the mechanisms by which T cells participate in the control of infection are still not completely defined. It is generally accepted that both, CD4 + and CD8 + T cells, are an essential component of protective immunity against TB [3]. CD4 + T cells are particularly critical during the early phase of infection, while CD8 + T cells appear to contribute mostly at later stages [4,5]. Both, CD4 + and CD8 + T cells, produce interferon-c (IFN-c) which in turn stimulates the anti-microbial activity of macrophages. Intracellular pathogens are then killed through reactive nitrogen intermediates produced by the inducible nitric oxide synthase [6] or through effector mechanisms mediated by the newly described member of the 47-kD guanosine triphosphatase family, . CD8 + T cells can also cause death of both target cells and their intracellular bacterial cargo, either through perforin-dependent cytolysis by the release of granzymes and granulysin, or by ligation of Fas ligand (FasL) on their surface with Fas on infected macrophages [5,[8][9][10]. Because CD8 + T cells are involved in protection during the chronic stage of TB [4,5,11], and participate in memory immune responses to Mtb infection [12], generating a more robust CD8 + T cell response may provide an effective vaccination strate...

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