Immunopathology of myositis, myocarditis and central nervous system involvement in trichinellosis.

Trichinella is the only nematode with an intracellular localization in the skeletal muscle cell. The presence of the parasite in the muscle tissue activates an inflammatory response, which can differ depending on the species: either a mixed Th1-Th2 (in humans) or a shift from Th1 to Th2 (in rodents). If the inflammatory response cannot kill the parasite, it leads however to a myositis at different degrees, depending mainly on the Trichinella species. After parasite invades the skeletal muscle cell, infiltration of macrophages, CD4+ and CD8+T cells, B cells occurs, with a production of high levels of reactive oxygen and nitrogen species such as nitric oxide. Eosinophils also play an important role during Trichinella infection. On one hand, for parasite survival, blocking Th1 response and producing IL-4 which could be beneficial for larval growth. On the other hand, Eosinophils but also other immunopathological phenomena are involved in the neurotrichinellosis, a condition which includes myocarditis as well as central nervous system involvement in severe cases.