The intracellular protozoan Toxoplasma gondii triggers rapid MAPK activation in mouse macrophages (Mφ). We used synthetic inhibitors and dominant-negative Mφ mutants to demonstrate that T. gondii triggers IL-12 production in dependence upon p38 MAPK. Chemical inhibition of stress-activated protein kinase/JNK showed that this MAPK was also required for parasite-triggered IL-12 production. Examination of upstream MAPK kinases (MKK) 3, 4, and 6 that function as p38 MAPK activating kinases revealed that parasite infection activates only MKK3. Nevertheless, in MKK3−/− Mφ, p38 MAPK activation was near normal and IL-12 production was unaffected. Recently, MKK-independent p38α MAPK activation via autophosphorylation was described. Autophosphorylation depends upon p38α MAPK association with adaptor protein, TGF-β-activated protein kinase 1-binding protein-1. We observed TGF-β-activated protein kinase 1-binding protein-1-p38α MAPK association that closely paralleled p38 MAPK phosphorylation during Toxoplasma infection of Mφ. Furthermore, a synthetic p38 catalytic-site inhibitor blocked tachyzoite-induced p38α MAPK phosphorylation. These data are the first to demonstrate p38 MAPK autophosphorylation triggered by intracellular infection.

Neutrophil migration to the site of infection is a critical early step in host immunity to microbial pathogens, in which chemokines and their receptors play an important role. In this work, mice deficient in expression of the chemokine receptor CXCR2 were infected with Toxoplasma gondii and the outcome was monitored. Gene-deleted animals displayed completely defective neutrophil recruitment, which was apparent at 4 h and sustained for at least 36 h. KitW/KitW-v animals also displayed defective polymorphonuclear leukocyte migration, suggesting mast cells as one source of chemokines driving the response. Tachyzoite infection and replication were accelerated in CXCR2−/− animals, resulting in establishment of higher cyst numbers in the brain relative to wild-type controls. Furthermore, serum and spleen cell IFN-γ levels in infected, gene-deleted mice were reduced 60–75% relative to infected normal animals, and spleen cell TNF-α was likewise reduced by ∼50%. These results highlight an important role for CXCR2 in neutrophil migration, which may be important for early control of infection and induction of immunity during Toxoplasma infection.

No abstract

Toll-like receptors (TLR) that signal through the common adaptor molecule myeloid differentiation factor 88 (MyD88) are essential in proinflammatory cytokine responses to many microbial pathogens. In this study we report that Toxoplasma gondii triggers neutrophil IL-12 and chemokine ligand 2 (CCL2; monocyte chemoattractant protein 1) production in strict dependence upon functional MyD88. Nevertheless, the responses are distinct. Although we identify TLR2 as the receptor triggering CCL2 production, parasite-induced IL-12 release did not involve this TLR. The production of both IL-12 and CCL2 was increased after neutrophil activation with IFN-γ. However, the synergistic effect of IFN-γ on IL-12, but not CCL2, was dependent upon Stat1 signal transduction. Although IL-10 was a potent down-regulator of Toxoplasma-triggered neutrophil IL-12 release, the cytokine had no effect on parasite-induced CCL2 production. Soluble tachyzoite Ag fractionation demonstrated that CCL2- and IL-12 inducing activities are biochemically distinct. Importantly, Toxoplasma cyclophilin-18, a molecule previously shown to induce dendritic cell IL-12, was not involved in neutrophil IL-12 production. Our results show for the first time that T. gondii possesses multiple molecules triggering distinct MyD88-dependent signaling cascades, that these pathways are independently regulated, and that they lead to distinct profiles of cytokine production.

No abstract

No abstract

No abstract

No abstract