Infected MyD88 Research Articles

In MyD88-/- mice infected with Mycobacterium tuberculosis ESAT6-specific CD4 T cells expand normally but display impaired IFN-γ production due to a T cell intrinsic role for the adaptor molecule (129.19)

Abstract MyD88-/- mice fail to control Mycobacterium tuberculosis (Mtb) replication and rapidly succumb to infection. This phenotype has been attributed to IL-R1 and TLR dependent defects in innate immunity although we have also described impaired Th1 cytokine production in these animals. It is unclear whether the partial defect in Th1 response is due to lack of expansion of antigen (Ag)-specific cells or their failure to differentiate into IFN-γ secreting cells. To address this, we stained with a MHC II tetramer to compare pulmonary I-Ab ESAT61-20 specific CD4 T cells in Mtb infected WT and MyD88-/- mice. Interestingly, expansion of Ag specific CD4 T cells was comparable in the two mouse strains. However, we repeatedly observed an approximate 50% reduction in the frequency of IFN-γ secreting Ag-specific cells in MyD88-/- mice, despite uniform T-bet expression. Non-competitive and competitive mixed BM chimeras were employed to determine whether this IFN-γ production defect reflects a T-cell intrinsic role for MyD88. In both strategies, a significant proportion of Ag-specific MyD88-/- T cells still failed to secrete IFN-γ upon re-stimulation when compared to T cells from WT chimeric controls or MyD88+/+ T cells in the same animal. Thus, in murine Mtb, MyD88 expression is dispensable for expansion but required for optimal IFN-γ secretion by Ag-specific CD4 T cells due largely to a T cell intrinsic function of the adaptor molecule. Work supported by NIAID Intramural Research Program.

Lack of MyD88 protects the immunodeficient host against fatal lung inflammation triggered by the opportunistic bacteria Burkholderia cenocepacia

Introduction Burkholderia cenocepacia is an opportunistic pathogen of major concern for cystic fibrosis patients as well as immunocompromised cancer patients and transplant recipients. The mechanisms by which B cenocepacia triggers a rapid health deterioration of the susceptible host have yet to be characterized. Toll-like receptors (TLR) and their key signaling intermediate myeloid differentiation (MyD)88 play a central role in the detection of microbial molecular patterns and in the initiation of an effective immune response. Here, we designed an investigation to better understand the role of TLR-MyD88 signaling in B cenocepacia -induced pathogenesis in the immunocompromized host, using an experimental murine model. Methodology The time-course of several dynamic parameters, including animal survival, bacterial load and secretion of critical inflammatory mediators, was compared in infected and immunosuppressed wild-type and MyD88 -/- mice. Results When compared to wild-type mice, infected MyD88 -/- animals displayed significantly reduced levels of inflammatory mediators (including KC, TNFα, IL-6, MIP-2 and G-CSF) in blood and lung airspaces. Moreover, despite a higher transient bacterial load in the lungs, immunosuppressed mice deficient in MyD88 had an unexpected survival advantage. Finally, we showed that this B cenocepacia -induced life-threatening infection of wild-type mice could be prevented by corticosteroids. Conclusions Our findings demonstrate that a MyD88-dependent pathway can critically contribute to a detrimental host inflammatory response that leads to fatal pneumonia.

MyD88 and IFN-αβ differentially control maturation of bystander but not Salmonella-associated dendritic cells or CD11cintCD11b+cells during infection

The interface between dendritic cells (DCs) and T cells is critical to elicit effective immunity against pathogens. The maturation state of DCs determines the quality of the interaction and governs the type of response. DCs can be matured directly through activating Toll-like receptors (TLRs) or indirectly by cytokines. We explore the role of the TLR adaptor MyD88 on DC maturation during Salmonella infection. Using Salmonella expressing GFP, we also examine the phenotype and function of bacteria-associated DCs matured in the absence of bacteria-mediated TLR signalling. MyD88 was required for upregulation of CD80 on DCs during infection, whereas CD86 and CD40 were upregulated independently of MyD88, although requiring a higher bacterial burden in the MLN. MyD88-independent upregulation was mediated by IFN-alphabeta produced during infection. In infected MyD88(-/-)IFN-alphabetaR(-/-) mice, which lack most bacteria-driven TLR signalling, indirect DC maturation was abolished. In contrast, DCs containing Salmonella upregulated co-stimulatory molecules independently of MyD88 and IFN-alphabeta, revealing a pathway of phenotypic maturation active in infected DCs. However, despite high co-stimulatory molecule expression, Salmonella-containing DCs from MyD88(-/-) or MyD88(-/-)IFN-alphabetaR(-/-) mice had a compromised capacity to activate T cells. Thus, bacterial stimulation of TLRs influences DC function at multiple levels that modulates their capacity to direct antibacterial immunity.

MyD88-dependent activation of dendritic cells and CD4 + T lymphocytes mediates symptoms, but is not required for the immunological control of parasites during rodent malaria

We investigated the role of different TLRs and MyD88 in host resistance to infection and malaria pathogenesis. TLR2 −/−, TLR4 −/−, TLR6 −/−, TLR9 −/− or CD14 −/− mice showed no change in phenotypes (parasitemia, body weight and temperature) when infected with Plasmodium chabaudi chabaudi (AS). MyD88 −/− mice displayed comparable ability to wild type animals in controlling and clearing parasitemia. Importantly, MyD88 −/− mice exhibited impaired production of TNF-α and IFN-γ as well as attenuated symptoms, as indicated by changes in body weight and temperature during parasitemia. Consistently, CD11b + monocytes and CD11c + dendritic cells from infected MyD88 −/− mice were shown impaired for production of pro-inflammatory cytokines, and in initiating CD4 + T cell responses. Importantly, the inhibition of T cell activation with anti-CD134L, mostly inhibited IFN-γ, partially inhibited TNF-α production, and protected the animals from malaria symptoms. Our findings suggest that MyD88 and possibly its associated TLRs expressed by dendritic cells play an important role in pro-inflammatory responses, T cell activation, and pathogenesis of malaria, but are not critical for the immunological control of the erythrocytic stage of P. chabaudi.

Dual Role of MyD88 in Rapid Clearance of Relapsing FeverBorreliaspp

Relapsing fever Borrelia spp. undergo antigenic variation, achieve high levels in blood, and require rapid production of immunoglobulin M (IgM) for clearance. MyD88-deficient mice display defective clearance of many pathogens; however, the IgM response to persistent infection is essentially normal. Therefore, MyD88(-/-) mice provided a unique opportunity to study the effect of nonantibody, innate host defenses to relapsing fever Borrelia. Infected MyD88(-/-) mice harbored extremely high levels of B. hermsii in the blood compared to wild-type littermates. In the comparison of MyD88(-/-) mice and B- and T-cell-deficient scid mice, two features stood out: (i) bacterial numbers in blood were at least 10-fold greater in MyD88(-/-) mice than scid mice, even though the production of IgM still occurred in MyD88(-/-) mice; and (ii) many of the MyD88(-/-) mice were able to exert partial clearance, although with delayed kinetics relative to wild-type mice, a feature not seen in scid mice. Further analysis revealed a delay in the IgM response to lipoproteins expressed by the original inoculum; however, by 6 days of infection antibodies were produced in MyD88(-/-) mice that could clear spirochetemia in scid mice. While these results indicated that the production of IgM was delayed in MyD88(-/-) mice, they also point to a second, antibody-independent role for MyD88 signaling in host defense to relapsing fever Borrelia. This second defect was apparent only when antibody levels were limiting.

TLRs 2 and 4 Are Not Involved in Hypersusceptibility to Acute Pseudomonas aeruginosa Lung Infections

TLRs are implicated in defense against microorganisms. Animal models have demonstrated that the susceptibility to a number of Gram-negative pathogens is linked to TLR4, and thus LPS of many Gram-negative bacteria have been implicated as virulence factors. To assess the role of this pathogen-associated molecular pattern as it is exposed on intact Pseudomonas aeruginosa, the susceptibility of mice lacking TLR4 or both TLR2 and TLR4 was examined in a model of acute Pseudomonas pneumonia. These mutant mice were not hypersusceptible to the Pseudomonas challenge and mounted an effective innate response that cleared the organism despite low levels of TNF-alpha and KC in the airways. Bacterial and neutrophil counts in the lung were similar in control and TLR-deficient mice at 6 and 24 h after infection. MyD88(-/-) mice were, however, hypersusceptible, with 100% of mice dying within 48 h with a lower dose of P. aeruginosa. Of note there were normal levels of IL-6 and G-CSF in the airways of TLR mutant mice that were absent from the MyD88(-/-) mice. Thus, the susceptibility of mice to P. aeruginosa acute lung infection does not go through TLR2 or TLR4, implying that Pseudomonas LPS is not the most important virulence factor in acute pneumonia caused by this organism. Furthermore, G-CSF treatment of infected MyD88(-/-) mice results in improved clearance and survival. Thus, the resistance to infection in TLR2/TLR4(-/-) mice may be linked to G-CSF and possibly IL-6 production.

Mycobacterial infection in MyD88-deficient mice.

MyD88 is an adaptor protein that plays a major role in TLR/IL-1 receptor family signaling. To understand the role of MyD88 in the development of murine tuberculosis in vivo, MyD88 knockout (KO) mice aerially were infected with Mycobacterium tuberculosis. Infected MyD88 mice were not highly susceptible to M. tuberculosis infection, but they developed granulomatous pulmonary lesions with neutrophil infiltration which were larger than those in wild-type (WT) mice (P < 0.01). The pulmonary tissue levels of mRNA for iNOS and IL-18 were slightly lower, but levels of mRNA for IL-1 beta, IL-2, IL-4, IL-6, IL-10, IFN-gamma, and TGF-beta were higher in MyD88 KO mice. IFN-gamma, TNF-alpha, IL-1 beta, and IL-12 also were high in the sera of MyD88 KO mice. There were no statistically significant differences in the expression of TNF-alpha, IL-12, and ICAM-1 mRNA between MyD88 KO and WT mice. Thus, MyD88 deficiency did not influence the development of murine tuberculosis. NF-kappa B activity was similar in the alveolar macrophages from the lung tissues of MyD88 KO and WT mice. Also, there may be a TLR2-specific, MyD88-independent IL-1 receptor/TLR-mediated pathway to activate NF-kappa B in the host defense against mycobacterial infection.