Nasiema Allie

Toll-Like Receptor 2-Deficient Mice Succumb to Mycobacterium tuberculosis Infection

Recognition of Mycobacterium tuberculosis by the innate immune system is essential in the development of an adaptive immune response. Mycobacterial cell wall components activate macrophages through Toll-like receptor (TLR) 2, suggesting that this innate immune receptor plays a role in the host response to M. tuberculosis infection. After aerosol infection with either 100 or 500 live mycobacteria, TLR2-deficient mice display reduced bacterial clearance, a defective granulomatous response, and develop chronic pneumonia. Analysis of pulmonary immune responses in TLR2-deficient mice after 500 mycobacterial aerosol challenge showed increased levels of interferon-gamma, tumor necrosis factor-alpha, and interleukin-12p40 as well as increased numbers of CD4(+) and CD8(+) cells. Furthermore, TLR2-deficient mice mounted elevated Ag-specific type 1 T-cell responses that were not protective because all deficient mice succumb to infection within 5 months. Taken together, the data suggests that TLR2 may function as a regulator of inflammation, and in its absence an exaggerated immune inflammatory response develops.

Increased resistance to mycobacterial infection in the absence of interleukin-10

Interleukin‐10 (IL‐10) down‐regulates T helper type 1 cell and macrophage functions. As IL‐10 is induced along with tumour necrosis factor (TNF) and IL‐12 in mycobacterial infection, we asked whether endogenous IL‐10 plays a role in the antimycobacterial response. We demonstrate here that IL‐10‐deficient mice eliminate Mycobacterium bovis Calmette–Guérin bacillus faster than wild‐type mice. Granulomas are significantly larger, containing more CD‐11b‐ and CD11c‐positive antigen‐presenting cells and T cells, and the expression of major histocompatibility complex class II and intracellular adhesion molecule‐1 is increased. Macrophages in granulomas of IL‐10‐deficient mice express high levels of TNF, acid phosphatase and inducible nitric oxide synthase (iNOS). Finally, an increased cutaneous delayed‐type hypersensitivity reaction to mycobacterial proteins is further evidence of an augmented cell‐mediated immune response. In conclusion, the cell‐mediated immunity is enhanced in the absence of IL‐10, resulting in a robust granuloma response, which accelerates the clearance of mycobacteria. Therefore, endogenous IL‐10 attenuates mycobacterial immunity.

Membrane TNF confers protection to acute mycobacterial infection

BackgroundTumour necrosis factor (TNF) is crucial for the control of mycobacterial infection as TNF deficient (KO) die rapidly of uncontrolled infection with necrotic pneumonia. Here we investigated the role of membrane TNF for host resistance in knock-in mice with a non-cleavable and regulated allele (mem-TNF).MethodsC57BL/6, TNF KO and mem-TNF mice were infected with M. tuberculosis H37Rv (Mtb at 100 CFU by intranasal administration) and the survival, bacterial load, lung pathology and immunological parameters were investigated. Bone marrow and lymphocytes transfers were used to test the role of membrane TNF to confer resistance to TNF KO mice.ResultsWhile TNF-KO mice succumbed to infection within 4–5 weeks, mem-TNF mice recruited normally T cells and macrophages, developed mature granuloma in the lung and controlled acute Mtb infection. However, during the chronic phase of infection mem-TNF mice succumbed to disseminated infection with necrotic pneumonia at about 150 days. Reconstitution of irradiated TNF-KO mice with mem-TNF derived bone marrow cells, but not with lymphocytes, conferred host resistance to Mtb infection in TNF-KO mice.ConclusionMembrane expressed TNF is sufficient to allow cell-cell signalling and control of acute Mtb infection. Bone marrow cells, but not lymphocytes from mem-TNF mice confer resistance to infection in TNF-KO mice. Long-term infection control with chronic inflammation likely disrupting TNF mediated cell-cell signalling, additionally requires soluble TNF.

Prominent role for T cell-derived Tumour Necrosis Factor for sustained control of Mycobacterium tuberculosis infection

Tumour Necrosis Factor (TNF) is critical for host control of M. tuberculosis, but the relative contribution of TNF from innate and adaptive immune responses during tuberculosis infection is unclear. Myeloid versus T-cell-derived TNF function in tuberculosis was investigated using cell type-specific TNF deletion. Mice deficient for TNF expression in macrophages/neutrophils displayed early, transient susceptibility to M. tuberculosis but recruited activated, TNF-producing CD4+ and CD8+ T-cells and controlled chronic infection. Strikingly, deficient TNF expression in T-cells resulted in early control but susceptibility and eventual mortality during chronic infection with increased pulmonary pathology. TNF inactivation in both myeloid and T-cells rendered mice critically susceptible to infection with a phenotype resembling complete TNF deficient mice, indicating that myeloid and T-cells are the primary TNF sources collaborating for host control of tuberculosis. Thus, while TNF from myeloid cells mediates early immune function, T-cell derived TNF is essential to sustain protection during chronic tuberculosis infection.

TNF in Host Resistance to Tuberculosis Infection

TNF is essential to control Mycobacterium tuberculosis infection and cannot be replaced by other proinflammatory cytokines. Overproduction of TNF may cause immunopathology, while defective TNF production results in uncontrolled infection. The critical role of TNF in the control of tuberculosis has been illustrated recently by primary and reactivation of latent infection in some patients under pharmacological anti-TNF therapy for rheumatoid arthritis or Crohns disease. In this review, we discuss results of recent studies aimed at better understanding of molecular, cellular and kinetic aspects of TNF-mediated regulation of host-mycobacteria interactions. In particular, recent data using either mutant mice expressing solely membrane TNF or specific inhibitor sparing membrane TNF demonstrated that membrane TNF is sufficient to control acute M. tuberculosis infection. This is opening the way to selective TNF neutralization that might retain the desired anti-inflammatory effect but reduce the infectious risk.

Tumor necrosis factor (TNF) receptor-1 (TNFp55) signal transduction and macrophage-derived soluble TNF are crucial for nitric oxide-mediated Trypanosoma congolense parasite killing.

Control of Trypanosoma congolense infections requires an early cell-mediated immune response. To unravel the role of tumor necrosis factor (TNF) in this process, 6 different T. congolense strains were used in 6 different gene-deficient mouse models that included TNF(-/-), TNF receptor-1 (TNFp55)(-/-), and TNF receptor-2 (TNFp75)(-/-) mice, 2 cell type-specific TNF(-/-) mice, as well as TNF-knock-in mice that expressed only membrane-bound TNF. Our results indicate that soluble TNF produced by macrophages/neutrophils and TNFp55 signaling are essential and sufficient to control parasitemia. The downstream mechanism in the control of T. congolense infection depends on inducible nitric oxide synthase activation in the liver. Such a role for nitric oxide is corroborated ex vivo, because the inhibitor N(G)-monomethyl-l-arginine blocks the trypanolytic activity of the adherent liver cell population, whereas exogenous interferon- gamma that stimulates nitric oxide production enhances parasite killing. In conclusion, the control of T. congolense infection depends on macrophage/neutrophil-derived soluble TNF and intact TNFp55 signaling, which induces trypanolytic nitric oxide.

Tumor Necrosis Factor Receptor 2 Plays a Minor Role for Mycobacterial Immunity

Tumor necrosis factor (TNF) signalling via the TNF receptor 1 (TNF-R1) is required for host resistance to mycobacterial infection. The role of TNF-R2 in anti-mycobacterial immunity is not known. Therefore, we compared TNF-R1 and TNF-R2 knockout (KO) mice infected with Mycobacterium bovis BCG (107 CFU, i.v.). While the bacterial burden of TNF-R1-deficient mice was significantly increased and the mice succumbed to infection between 4 and 5 weeks, TNF-R2 KO mice were less sensitive, and only 3 of 10 mice died within 12 weeks. Wild-type (WT) mice were resistant to BCG infection. The inability to clear the infection of TNF-R1 KO mice was associated with a reduced delayed-type hypersensitivity (DTH) response to purified protein derivative and severe impairment in forming granulomas with reduced macrophage recruitment and activation, and diminished expression of adhesion molecules. By contrast, TNF-R2 KO mice developed normal DTH response and mature mycobactericidal granulomas as the WT mice. Therefore, anti-mycobacterial immunity is largely dependent on TNF signalling via the TNF-R1, while activation of TNF-R2 plays a minor role.

Protective role of membrane tumour necrosis factor in the host’s resistance to mycobacterial infection

Tumour necrosis factor‐α (TNF‐α) plays a critical role in the recruitment and activation of mononuclear cells in mycobacterial infection. The role of membrane TNF, in host resistance against Mycobacterium bovis bacille Calmette–Guérin (BCG), was tested in knock‐in mice in which the endogenous TNF was replaced by a non‐cleavable and regulated allele (Δ1–12, TNFtm/tm). While 100% of mice with complete TNF deficiency (TNF−/−) succumbed to infection, 50% of TNFtm/tm mice were able to control M. bovis BCG infection and survived the experimental period. Membrane expressed TNF allowed a substantial recruitment of activated T cells and macrophages with granuloma formation and expression of bactericidal inducible nitric oxide synthase (iNOS). Using virulent Mycobacterium tuberculosis infection we confirm that membrane TNF conferred partial protection. Infection in TNFtm/tm double transgenic mice with TNF‐R1 or TNF‐R2 suggest protection is mediated through TNF‐R2 signalling. Therefore, the data suggest that membrane‐expressed TNF plays a critical role in host defence to mycobacterial infection and may partially substitute for soluble TNF.

Enhanced immune response in Mycobacterium bovis Bacille Calmette Guerin (BCG)-infected IL-10-deficient mice

Abstract The role of the endogenous interleukin-10 (IL-10) in the control of Mycobacterium bovis Bacille Calmette Guerin (BCG) infection was assessed using IL-10-deficient (IL-10-/-)mice. Similar to wild-type (WT) mice, IL-10-/- mice were resistant to intravenous challenge with Mycobacterium bovis BCG. Significantly higher plasma concentrations of IL-12 and tumour necrosis factor (TNF) indicated an elevated protective immune response of IL-10-/- mice. Determination of bacilli burden in IL-10-/- mice showed accelerated clearance in the lungs, spleen and the liver in comparison to WT mice. Enhanced inflammation and a vigorous granulomatous response accompanied accelerated mycobacterial clearance. Immunohistochemical analysis of hepatic granulomas from IL-10-/- mice revealed augmented lymphocyte recruitment and macrophage activation, such as increased major histocompatibility complex (MHC) class II and inducible nitric oxide synthase (iNOS) expression. Further, it was found that enlarged granulomas persisted subsequent to mycobacterial clearance and failed to resolve in the absence of IL-10. In conclusion, endogenous IL-10 dampens the cell-mediated immune response to mycobacterial infection.

Roles of soluble and membrane TNF and related ligands in mycobacterial infections: effects of selective and non-selective TNF inhibitors during infection

TNF plays an essential and non-redundant role in host defense mechanisms against Mycobacterium tuberculosis (Mtb) infection. TNF contributes to the development of granulomas, microstructures encasing pathogens and concentrating interactions between phagocytes and lymphocytes, and promotes bactericidal pathways to limit and destroy the invading intracellular pathogen. Production of TNF is associated with the development of human inflammatory diseases, and its inhibition, although an effective therapy, increases the risk of infections including either new or reactivation of tuberculosis infection. Studies on the role of membrane TNF in the absence of secreted TNF using genetic mouse models have shown that membrane TNF protects from M. bovis BCG and acute M. tuberculosis infections but does not induce inflammation in mouse. Pharmacological approaches of selective and non-selective soluble TNF inhibition show that a selective inhibitor of soluble TNF does not suppress host immunity to M. tuberculosis and M. bovis BCG infections, yet protects mice from arthritis and liver inflammatory diseases. This suggests that neutralization of soluble TNF may be effective to inhibit inflammatory diseases and also reduce the infection risks associated with current anti-TNF therapies.