Mouse Neutrophils Require JNK2 MAPK for Toxoplasma gondii-Induced IL-12p40 and CCL2/MCP-1 Release

The MAPK family member JNK/stress-activated MAPK (SAPK) is involved in extracellular stress and proinflammatory cytokine responses, including production of cytokines such as IL-12. The JNK1 and 2 isoforms are widely expressed, but JNK3 is largely restricted to tissues of the brain, testis, and heart. In this study, we focus on mouse neutrophils, a cell type in which JNK/SAPK expression and activity has been given little study. We used Western blot analysis to examine expression patterns of JNK/SAPK in wild-type and JNK2-/- polymorphonuclear leukocytes (PMN). Surprisingly, neutrophils displayed a major deficiency in JNK1 expression, in contrast to macrophages that expressed high levels of both JNK1 and JNK2 MAPK. JNK1 expression was steadily reduced during the neutrophil maturation in bone marrow. We used PMN infection with the protozoan parasite Toxoplasma gondii to determine whether neutrophil JNK2 was functional. The parasite induced rapid JNK2 phosphorylation and intracellular FACS staining demonstrated preferential activation in infected neutrophils. Use of JNK2-/- neutrophils revealed that this MAPK family member was required for PMN IL-12p40 and CCL2/MCP-1 production. The chemotactic response displayed a minor JNK2 dependence but phagocytosis and oxidative burst activity did not require this MAPK. These findings are important because they demonstrate 1) a previously unrecognized unusual JNK expression pattern in mouse neutrophils, 2) JNK2 in PMN is activated by Toxoplasma invasion, and 3) a requirement for JNK2 in PMN IL-12p40 and CCL2/MCP-1 production in response to a microbial pathogen.