Progress on Immunopathogenesis of Hepatic Fibrosis by Schistosome Infections

Schistosomiasis is a widespread zoonosis. It seriously threats human health. Schistosomiasis is caused by schistosomes, which belong to Schistosoma genus, a kind of blood-dwelling fluke worms, mainly living in the venus portal-mesenteric system of human by digenetic intravascular parasite. People who infected by schistosomes may appear the symptoms with abdominal pain, diarrhea, anemia, and splenomegaly, progressing from egg-granulomas eventually to hepatic fibrosis. This review describes hepatic fibrosis caused by schistosomes, Clonorchis sinensis and Toxoplasma gondii, Capillaria hepatica and hydatid, mainly focused on the hepatic fibrosis caused by S. mansoni and S. japonicum. T helper (Th) cells (Th1, Th2, Th17 and Treg cells) play an important role in the process of anti-schistosomiasis infection and immune regulation. Especially, the balance of Th1/Th2, Th17/Treg is closely related to the development of hepatic fibrosis. Th2 and Th17 cells can promote the granuloma formation by the secretion of IL-4 and IL-17 respectively; while Th1 and Treg cells can suppress the granuloma formation. These CD4+ T cell subsets are in complicated cross-talk in schistosomiasis immunity. Hepatic fibrosis caused by these parasites are also the key and difficult points of prevention and treatment of parasitic diseases, with further study about their molecular mechanism will provide us more thinking about parasitic effective prevention and treatment.