Toxoplasma gondii-Induced Neutrophil Extracellular Traps Amplify the Innate and Adaptive Response.

Toxoplasmosis affects one-third of the human population worldwide. Humans are accidental hosts and are infected after consumption of undercooked meat and water contaminated with Toxoplasma gondii cysts and oocysts, respectively. Neutrophils have been shown to participate in the control of T. gondii infection in mice through a variety of effector mechanisms, such as reactive oxygen species (ROS) and neutrophil extracellular trap (NET) formation. However, few studies have demonstrated the role of neutrophils in individuals naturally infected with T. gondii. In the current study, we evaluated the activation status of neutrophils in individuals with acute or chronic toxoplasmosis and determined the role of T. gondii-induced NET formation in the amplification of the innate and adaptive immune responses. We observed that neutrophils are highly activated during acute infection through increased expression of CD66b. Moreover, neutrophils from healthy donors (HDs) cocultured with tachyzoites produced ROS and formed NETs, with the latter being dependent on glycolysis, succinate dehydrogenase, gasdermin D, and neutrophil elastase. Furthermore, we observed elevated levels of the chemokines (CXC motif) CXCL8 and (CC motif) CCL4 ligands in plasma from patients with acute toxoplasmosis and production by neutrophils from HDs exposed to T. gondii. Finally, we showed that T. gondii-induced NETs activate neutrophils and promote the recruitment of autologous CD4+ T cells and the production of interferon gamma (IFN-γ), tumor necrosis factor (TNF), interleukin 6 (IL-6), IL-17, and IL-10 by peripheral blood mononuclear cells. In conclusion, we demonstrated that T. gondii activates neutrophils and promotes the release of NETs, which amplify human innate and adaptive immune responses. IMPORTANCE Approximately one-third of the human population is estimated to be chronically infected with the obligate intracellular parasite Toxoplasma gondii. Humans are accidental hosts that are infected with T. gondii after consumption of undercooked meat or contaminated water. Neutrophils have been shown to control T. gondii growth by different mechanisms, including neutrophil extracellular traps (NETs). In the current study, we observed that neutrophils are highly activated during acute toxoplasmosis. We also determined that T. gondii-induced NETs are dependent on the energetic profile of neutrophils as well as the production of ROS and gasdermin D (GSDMD) cleavage. In addition, we showed that T. gondii-induced NETs activate neutrophils, promote the recruitment of autologous CD4+ T cells, and induce the production of cytokines by peripheral blood mononuclear cells, amplifying the innate and adaptive immune responses.

Intercellular adhesion molecule 1 deficiency leads to impaired recruitment of T lymphocytes and enhanced host susceptibility to infection with Trypanosoma cruzi.

In this study, we investigated the involvement of Th1 cytokines in the expression of cell adhesion molecules (CAM) and recruitment of inflammatory cells to the heart of mice infected with Trypanosoma cruzi. Our results show that endogenously produced IFN-gamma is essential to induce optimal expression of VCAM-1 and ICAM-1 on the cardiac vascular endothelium of infected mice. Furthermore, the influx of inflammatory cells into the cardiac tissue was impaired in Th1 cytokine-deficient infected mice, paralleling the intensity of VCAM-1 and ICAM-1 expression on the vascular endothelium. Consistent with the importance of ICAM-1 in host resistance, ICAM-1 knockout (KO) mice were highly susceptible to T. cruzi infection, as assessed by mortality rate, parasitemia, and heart tissue parasitism. The enhanced parasitism was associated with a decrease in the numbers of CD4(+) and CD8(+) T lymphocytes in the heart tissue of ICAM-1 KO mice. Additionally, ICAM-1 KO mice mounted an unimpaired IFN-gamma response and IFN-gamma-dependent production of reactive nitrogen intermediates and parasite- specific IgG2a. Supporting the participation of ICAM-1 in cell migration during T. cruzi infection, the entrance of adoptively transferred PBL from T. cruzi-infected wild-type C57BL/6 mice into the cardiac tissue of ICAM-1 KO mice was significantly abrogated. Therefore, we favor the hypothesis that ICAM-1 plays a crucial role in T lymphocyte recruitment to the cardiac tissue and host susceptibility during T. cruzi infection.

Long-term protective immune response elicited by vaccination with an expression genomic library of Toxoplasma gondii.

Immunization of BALB/c mice with an expression genomic library of Toxoplasma gondii induces a Th1-type immune response, with recognition of several T. gondii proteins (21 to 117 kDa) and long-term protective immunity against a lethal challenge. These results support further investigations to achieve a multicomponent anti-T. gondii DNA vaccine.