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Structural deficiencies in granuloma formation in TNF gene-targeted mice underlie the heightened susceptibility to aerosol Mycobacterium tuberculosis infection, which is not compensated for by lymphotoxin.

The Journal of Immunology Author Choice

physiology, Aerosols, Animals, Cell Movement, immunology, Gene Targeting, Genetic Predisposition to Disease, Granuloma, Respiratory Tract, genetics, pathology, Hypersensitivity, Delayed, etiology, Immunophenotyping, Injections, Subcutaneous, Interferon-gamma, metabolism, Lymphocyte Activation, Lymphocyte Count, Administration, Inhalation, Lymphotoxin-alpha, Mice, Mice, Inbred C57BL, Mice, Knockout, Mycobacterium tuberculosis, Nitrites, T-Lymphocytes, Tuberculin, administration & dosage, Tuberculosis, prevention & control, Tumor Necrosis Factor-alpha, deficiency

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      Abstract

      TNF and lymphotoxin-alpha (LT alpha) may act at various stages of the host response to Mycobacterium tuberculosis. To dissect the effects of TNF independent of LT alpha, we have used C57BL/6 mice with a disruption of the TNF gene alone (TNF-/-). Twenty-one days following aerosol M. tuberculosis infection there was a marked increase in the number of organisms in the lungs of TNF-/- mice, and by 28-35 days all animals had succumbed, with widespread dissemination of M. tuberculosis. In comparison with the localized granulomas containing activated macrophages and T cells in lungs and livers of C57BL/6 wild-type (wt) mice, cellular infiltrates in TNF-/- mice were poorly formed, with extensive regions of necrosis and neutrophilic infiltration of the alveoli. Phenotypic analysis of lung homogenates demonstrated similar numbers of CD4+ and CD8+ T cells in TNF-/- and wt mice, but in TNF-deficient mice the lymphocytes were restricted to perivascular and peribronchial areas rather than colocated with macrophages in granulomas. T cells from TNF-/- mice retained proliferative and cytokine responses to purified protein derivative, and delayed-type hypersensitivity to purified protein derivative was demonstrable. Macrophages within the lungs of TNF-/- and wt mice showed similar levels of MHC class II and inducible nitric oxide synthase expression, and levels of serum nitrite were comparable. Thus, the enhanced susceptibility of TNF-/- is not compensated for by the presence of LT alpha, and the critical role of TNF is not in the activation of T cells and macrophages but in the local organization of granulomas.

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