IL-10 Impairs Local Immune Response in Lung Granulomas and Lymph Nodes during Early Mycobacterium tuberculosis Infection.

Tuberculosis (TB), caused by Mycobacterium tuberculosis, continues to be a major global health problem. Lung granulomas are organized structures of host immune cells that function to contain the bacteria. Cytokine expression is a critical component of the protective immune response, but inappropriate cytokine expression can exacerbate TB. Although the importance of proinflammatory cytokines in controlling M. tuberculosis infection has been established, the effects of anti-inflammatory cytokines, such as IL-10, in TB are less well understood. To investigate the role of IL-10, we used an Ab to neutralize IL-10 in cynomolgus macaques during M. tuberculosis infection. Anti-IL-10-treated nonhuman primates had similar overall disease outcomes compared with untreated control nonhuman primates, but there were immunological changes in granulomas and lymph nodes from anti-IL-10-treated animals. There was less thoracic inflammation and increased cytokine production in lung granulomas and lymph nodes from IL-10-neutralized animals at 3-4 wk postinfection compared with control animals. At 8 wk postinfection, lung granulomas from IL-10-neutralized animals had reduced cytokine production but increased fibrosis relative to control animals. Although these immunological changes did not affect the overall disease burden during the first 8 wk of infection, we paired computational modeling to explore late infection dynamics. Our findings support that early changes occurring in the absence of IL-10 may lead to better bacterial control later during infection. These unique datasets provide insight into the contribution of IL-10 to the immunological balance necessary for granulomas to control bacterial burden and disease pathology in M. tuberculosis infection.

Chronic granulomatous disease presenting as aseptic ascites in a 2-year-old child.

Chronic granulomatous disease (CGD) is a rare inherited immunodeficiency syndrome that results from abnormal nicotinamide adenine dinucleotide phosphate (NADPH) oxidase function. This defect leads to recurrent catalase-positive bacterial and fungal infections as well as associated granuloma formation. We review the case of a 2-year-old boy who presented with ascites and fever of an unknown origin as manifestations of CGD. Cultures were negative for infection throughout his course, and CGD was suspected after identification of granulomas on peritoneal biopsy. Genetic testing revealed a novel mutation in the CYBB gene underlying his condition. This paper highlights the importance of considering CGD in the differential diagnosis of fever of unknown origin and ascites in children.

CD4(+) regulatory T cells in a cynomolgus macaque model of Mycobacterium tuberculosis infection.

BACKGROUND: Mycobacterium tuberculosis infection in humans results in either latent infection or active tuberculosis. We sought to determine whether a higher frequency of regulatory T (T(reg)) cells predispose an individual toward active disease or whether T(reg) cells develop in response to active disease. METHODS: In cynomolgus macaques infected with a low dose of M. tuberculosis, approximately 50% develop primary tuberculosis, and approximately 50% become latently infected. Forty-one animals were monitored for 6-8 months to assess the correlation of the frequency of Foxp3(+) cells in peripheral blood and airways with the outcome of infection. RESULTS: In all animals, the frequency of T(reg) cells (CD4(+)Foxp3(+)) in peripheral blood rapidly decreased and simultaneously increased in the airways. Latently infected monkeys had a significantly higher frequency of T(reg) cells in peripheral blood before infection and during early infection, compared with monkeys that developed active disease. Monkeys with active disease experienced increased frequencies of T(reg) cells among peripheral blood mononuclear cells as they developed disease. CONCLUSIONS: Our data suggest that increased frequencies of T(reg) cells in active disease occur in response to increased inflammation rather than act as a causative factor in progression to active disease.

Aberrant TGF-beta signaling reduces T regulatory cells in ICAM-1-deficient mice, increasing the inflammatory response to Mycobacterium tuberculosis.

Foxp3+ T regulatory cells are required to prevent autoimmune disease, but also prevent clearance of some chronic infections. While natural T regulatory cells are produced in the thymus, TGF-beta1 signaling combined with T-cell receptor signaling induces the expression of Foxp3 in CD4+ T cells in the periphery. We found that ICAM-1-/- mice have fewer T regulatory cells in the periphery than WT controls, due to a role for ICAM-1 in induction of Foxp3 expression in response to TGF-beta1. Further investigation revealed a functional deficiency in the TGF-beta1-induced translocation of phosphorylated Smad3 from the cytoplasmic compartment to the nucleus in ICAM-1-deficient mice. This impairment in the TGF-beta1 signaling pathway is most likely responsible for the decrease in T regulatory cell induction in the absence of ICAM-1. We hypothesized that in the presence of an inflammatory response, reduced production of inducible T regulatory cells would be evident in ICAM-1-/- mice. Indeed, following Mycobacterium tuberculosis infection, ICAM-1-/- mice had a pronounced reduction in T regulatory cells in the lungs compared with control mice. Consequently, the effector T-cell response and inflammation were greater in the lungs of ICAM-1-/- mice, resulting in morbidity due to overwhelming pathology.

Tuberculous granulomas are hypoxic in guinea pigs, rabbits, and nonhuman primates.

Understanding the physical characteristics of the local microenvironment in which Mycobacterium tuberculosis resides is an important goal that may allow the targeting of metabolic processes to shorten drug regimens. Pimonidazole hydrochloride (Hypoxyprobe) is an imaging agent that is bioreductively activated only under hypoxic conditions in mammalian tissue. We employed this probe to evaluate the oxygen tension in tuberculous granulomas in four animal models of disease: mouse, guinea pig, rabbit, and nonhuman primate. Following infusion of pimonidazole into animals with established infections, lung tissues from the guinea pig, rabbit, and nonhuman primate showed discrete areas of pimonidazole adduct formation surrounding necrotic and caseous regions of pulmonary granulomas by immunohistochemical staining. This labeling could be substantially reduced by housing the animal under an atmosphere of 95% O(2). Direct measurement of tissue oxygen partial pressure by surgical insertion of a fiber optic oxygen probe into granulomas in the lungs of living infected rabbits demonstrated that even small (3-mm) pulmonary lesions were severely hypoxic (1.6 +/- 0.7 mm Hg). Finally, metronidazole, which has potent bactericidal activity in vitro only under low-oxygen culture conditions, was highly effective at reducing total-lung bacterial burdens in infected rabbits. Thus, three independent lines of evidence support the hypothesis that hypoxic microenvironments are an important feature of some lesions in these animal models of tuberculosis.

Neutralization of tumor necrosis factor (TNF) by antibody but not TNF receptor fusion molecule exacerbates chronic murine tuberculosis.

Tumor necrosis factor (TNF) plays an essential role in the immunologic maintenance of Mycobacterium tuberculosis infection. Although an increased rate of tuberculosis has been reported in humans treated with anti-TNF biological agents, disparate rates of disease have been observed between those treated with infliximab, an anti-TNF antibody, and etanercept, a TNF-neutralizing TNF receptor (TNFR) fusion molecule. We compared the effects of anti-TNF antibody and soluble TNFR fusion molecule in the murine model of tuberculosis. Systemic TNF neutralization was equivalent between these molecules, and both resulted in rapid morbidity at the initiation of infection. During chronic infection, administration of the receptor fusion molecule allowed the control of infection, whereas antibody treatment caused mice to die within a month. We provide evidence of decreased penetration into the granulomas by the receptor fusion molecule, compared with antibody. These findings begin to clarify the mechanistic difference between anti-TNF agents and their role in the exacerbation of tuberculosis.