Mouse bone marrow-derived macrophages infected with T. gondii (Type I, RH strain) for 6 hr

Toxoplasma gondii is a globally distributed parasite pathogen that infects virtually all warm-blooded animals. A hallmark of immunity to acute infection is the production of IFN- and IL-12, followed by a protective T cell response that is critical for parasite control. Nave T cell activation requires both TCR stimulation and the engagement of costimulatory receptors. Because of their important function in activating T cells, the expression of co-stimulatory ligands is believed to be under tight control. The molecular mechanisms governing their induction during microbial stimulation, however, are not well understood. We found that all three strains of T. gondii (Types I, II, and III) up-regulated the expression of B7-2, but not B7-1, on the surface of mouse bone marrow-derived macrophages. This induction occurred at the transcriptional level, required active parasite invasion, and was not dependent on MyD88 or TRIF. Genome-wide transcriptional analysis comparing infected and uninfected macrophages revealed the activation of MAPK signaling in infected cells. Using specific inhibitors against MAPKs, we determined that parasite-induced B7-2 is dependent on JNK, but not ERK or p38 signaling. We also observed that T. gondii-induced B7-2 expression on human peripheral blood monocytes is dependent on JNK signaling, indicating that a common mechanism of B7-2 regulation by T. gondii may exist in both humans and mice.

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