Host immunity against parasitic infections are complicated. It will be categorized into four immunological pathways against four types of parasitic infections. For intracellular protozoa, the host immunological pathway is TH1 immunity with macrophages, IFNg CD4 T cells, CD8 T cells, and IgG3 B cells. For free-living extracellular protozoa, the host immunological pathway is TH22 immunity with neutrophils, IL-22/IL-17 CD4 T cells, and IgG2 B cells. For helminths (endoparasites), the host

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... ical pathway is TH2a immunity with eosinophils, IL-5/IL-4 CD4 T cells, and IgG4 B cells. For insects (ectoparasites), the host immunological pathway is TH2b immunity with basophils, mast cells, IL-3/IL-4 CD4 T cells, and IgE B cells. Thus, the framework of the whole immunological pathways against four types of parasitic infection is given.