Trypanosoma cruzi infection in tumor necrosis factor receptor p55- deficient mice

Abstract

Tumor necrosis factor receptor p55 (TNFRp55) mediates host resistance to several pathogens by allowing microbicidal activities of phagocytes. In the studies reported here, TNFRp55(-/-) mice infected with the intracellular parasite Trypanosoma cruzi showed clearly higher parasitemia and cumulative mortality than wild-type (WT) controls did. However, gamma interferon (IFN- γ)-activated macrophages from TNFRp55(-/-) mice produced control levels of nitric oxide and killed the parasite efficiently in vitro. Trypanocidal mechanisms of nonphagocytic cells (myocardial fibroblasts) from both TNFRp55(-/-) and WT mice were also activated by IFN-γ in a dose-dependent way. However, IFN-γ-activated TNFRp55(-/-) nonphagocytes showed less effective killing of T. cruzi than WT control nonphagocytes, even when interleukin 1β (IL-1β) was added as a costimulator. In vivo, T. cruzi- infected TNFRp55(-/-) mice and WT mice released similar levels of NO and showed similar levels of IFN-γ mRNA and inducible nitric oxide synthase mRNA in their tissues. Instead, increased susceptibility to T. cruzi of TNFRp55(- /-) mice was associated with reduced levels of parasite-specific immunoglobulin G (IgG) (but not IgM) antibodies during infection, which is probably linked to abnormal B-cell differentiation in secondary lymphoid tissues of the mutant mice. Surprisingly, T. cruzi-infected TNFRp55(-/-) mice showed increased inflammatory and necrotic lesions in several tissues, especially in skeletal muscles, indicating that TNFRp55 plays an important role in controlling the inflammatory process. Accordingly, levels of Mn2+ superoxide dismutase mRNA, a TNF-induced enzyme which protects the cell from the toxic effects of superoxide, were lower in mutant than in WT infected mice.