CD40, autophagy and Toxoplasma gondii

Toxoplasmagondii represents a pathogen that survives within host cells by preventing the endosomal-lysosomal compartments from fusing with the parasitophorous vacuoles. The dogma had been that the non-fusogenic nature of these vacuoles is irreversible. Recent studies revealed that this dogma is not correct. Cell-mediated immunity through CD40 re-routes the parasitophorous vacuoles to the lysosomal compartment by a process called autophagy. Autophagosome formation around the parasitophorous vacuole results in killing of the T. gondii. CD40-induced autophagy likely contributes to resistance against T. gondii particularly in neural tissue

Toxoplasma gondii Infection of Neurons Induces Neuronal Cytokine and Chemokine Production, but Gamma Interferon- and Tumor Necrosis Factor-Stimulated Neurons Fail To Inhibit the Invasion and Growth of T. gondii

The intracellular parasite Toxoplasma gondii has the capacity to persist in the brain within neurons. In this study we demonstrated that T. gondii infected murine cerebellar neurons in vitro and replicated within these cells. Stimulation with gamma interferon (IFN-γ) and/or tumor necrosis factor (TNF) did not enable neurons to inhibit parasite invasion and replication. Cultured neurons constitutively produced interleukin 1 (IL-1), IL-6, macrophage inflammatory protein 1α (MIP-1α), and MIP-1β but not transforming growth factor β1 (TGF-β1), IL-10, and granulocyte-macrophage colony-stimulating factor. Neuronal expression of some cytokines (IL-6, TGF-β1) and chemokines (MIP-1β) was regulated by infection and/or by IFN-γ and TNF

Migratory Activation of Primary Cortical Microglia upon Infection with Toxoplasma gondii ▿ †

Disseminated toxoplasmosis in the central nervous system (CNS) is often accompanied by a lethal outcome. Studies with murine models of infection have focused on the role of systemic immunity in control of toxoplasmic encephalitis, while knowledge remains limited on the contributions of resident cells with immune functions in the CNS. In this study, the role of glial cells was addressed in the setting of recrudescent Toxoplasma infection in mice. Activated astrocytes and microglia were observed in the close vicinity of foci with replicating parasites in situ in the brain parenchyma. Toxoplasma gondii tachyzoites were allowed to infect primary microglia and astrocytes in vitro. Microglia were permissive to parasite replication, and infected microglia readily transmigrated across transwell membranes and cell monolayers. Thus, infected microglia, but not astrocytes, exhibited a hypermotility phenotype reminiscent of that recently described for infected dendritic cells. In contrast to gamma interferon-activated microglia, Toxoplasma-infected microglia did not upregulate major histocompatibility complex (MHC) class II molecules and the costimulatory molecule CD86. Yet Toxoplasma-infected microglia and astrocytes exhibited increased sensitivity to T cell-mediated killing, leading to rapid parasite transfer to effector T cells in vitro. We hypothesize that glial cells and T cells, besides their role in triggering antiparasite immunity, may also act as “Trojan horses,” paradoxically facilitating dissemination of Toxoplasma within the CNS. To our knowledge, this constitutes the first report of migratory activation of a resident CNS cell by an intracellular parasite

Measurement of Induced Cytokines in AIDS Clinical Trials Using Whole Blood: A Preliminary Report

Measures of immune function have become increasingly important as endpoints in AIDS clinical trials, with respect to both modulation and reconstitution of immunity by experimental therapies. Measurement of immune function in this setting requires the development of robust analytic approaches suitable for the clinical laboratory. Experiments were performed to evaluate the suitability of using cultured heparinized (“whole”) blood for induction of tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ), two cytokines critical in AIDS pathogenesis. TNF-α expression ranged from 229 to 769 pg/ml in lipopolysaccharide (LPS)-stimulated cultures and was not detected in unstimulated cultures. IFN-γ expression ranged from 0 to 112,000 pg/ml in phytohemagglutinin A (PHA)-stimulated cultures and from 0 to 789 pg/ml in antigen-stimulated cultures. The mean coefficient of variation observed in three weekly determinations was 0.47 for TNF-α and ranged from 0.12 to 1.73 for IFN-γ. These values indicate that sample sizes of 8, 24, and 29 subjects would be sufficient to detect twofold changes in LPS-induced TNF-α and in PHA- and antigen-induced IFN-γ, respectively, if two baseline and two treatment determinations were obtained, and if the interpatient variability of changes in true levels from baseline to follow-up is negligible compared to the variability in the three weekly measurements. Measurement of LPS-induced TNF-α and mitogen- or antigen-induced IFN-γ can be performed simply and reproducibly in human immunodeficiency virus-infected persons by the whole-blood culture method. Further studies are warranted to determine the effect of overnight shipping on assay reproducibility and to determine the extent to which responses can be reliably detected in subjects with low CD4 cell numbers

Characteristics and critical function of CD8+ T cells in the Toxoplasma-infected brain

The rise of the AIDS epidemic made the requirement for T cells in our continuous protection from pathogens critically apparent. The striking frequency with which AIDS patients exhibited profound neurological pathologies brought attention to many chronic infections that are latent within theimmune-privileged CNS. One of the most common lethal opportunistic infections of these patients was with the protozoan parasite, Toxoplasma gondii. Reactivation of Toxoplasma cysts within the brain causes massive tissue destruction evidenced as multiple ring-enhancing lesions on MRI and is called Toxoplasmic encephalitis (TE). TE is not limited to AIDS patients, but rather is a risk for all severely immunocompromised patients, including recipients of chemotherapy or transplant recipients. The lessons learned from these patient populations are supported by T cell depletion studies in mice. Such experiments have demonstrated that CD4+ and CD8+ T cells are required for protection against TE. Although it is clear that these T cell subsets work synergistically to fight infection, much evidence has been generated that suggests CD8+ T cells play a dominant role in protection during chronic toxoplasmosis. . In other models of CNS inflammation, such as intracerebral infection with LCMV and experimental autoimmune encephalomyelitis (EAE), infiltration of T cells into the brain is harmful and even fatal. In the brain of the immunocompetent host, the well-regulated T cell response to Toxoplasma gondii is therefore an ideal model to understand a controlled inflammatory response to CNS infection. This review will examine our current understanding of CD8+ T cells in the CNS during T. gondii infection in regards to the 1) mechanisms governing entry into the brain, 2) cues that dictate behavior within the brain, and 3) the functional and phenotypic properties exhibited by these cell