【正文】 ilar to molecules present in the haemolymph of the snail host. The parasite is thus seen as “self”. Helminth immune evasion strategies. Helminth immune evasion mechanisms in the invertebrate host. ? Immunosupression – developing microfilariae of Brugia pahangi amp。 integrin CR3 amp。 trematode worms, is able to adsorb host ponents, . RBC Ags, thus giving the worm the immunological appearance of host tissue. Schistosomes take up host blood proteins, . blood group antigens amp。 to ensure vector transmission. ? Chronic infections (from a few months to many years) are normal, therefore parasite needs to avoid immune elimination. ? Parasites have evolved immune evasion strategies. Protozoan immune evasion strategies. 1. Anatomical seclusion in the vertebrate host. ? Parasites may live intracellularly. By replicating inside host cell parasites avoid immune response. ? Plasmodium lives inside Red Blood Cells (RBC?S) which have no nucleus, when infected not recognised by CTL?s amp。 IgE activated to initiate inflammatory response in the intestine or lungs to expel the worms. These histamine elicited reactions are similar to allergic reactions. Vertebrate Immune responses to helminth infections. ? The acute response after previous exposure can involve an IgE and eosinophil mediated systemic inflammation which results in expulsion of the worms. Vertebrate Immune responses to helminth infections. ? Chronic exposure to worm antigens can cause chronic inflammation: – Delayed type hypersensitivity (DTH), Th1 / activated macrophages which can result in granulomas. – Th2 / B cell responses increase IgE, mast cells amp。 release of mediators, . histamine. ? Nephropathy immune plexes (parasite antigens, antibody + plement) in kidney (. malaria, schistosomiasis). Vertebrate Immune responses to Protozoan parasites. Innate immune responses. ? In vertebrates, extracellular protozoa are eliminated by phagocytosis and plement activation. ? T cell responses. Extracellular protozoa Th2 cytokines released for antibody production. Intracellular protozoa Cytotoxic lymphocytes (CTL?s) kill infected cells. Th1 cytokines produced to activate macrophages, CTL?s amp。 feeding on or causing destruction of cells = anaemia). ? Mechanical blockage (. Ascaris in intestine). ? However, severe disease often has a specific immune or inflammatory ponent. Immunopathology. Some examples include: ? Cerebral malaria TNF, IFN amp。 veterinary importance successfully adapted to innate amp。Evasion of Immunity 2 Immunity to specific parasites amp。 itching is called cercarial dermatitis (or ?swimmers itch?). In the natural duck host, larval stages develop into established infection with adult worms. Immunoparasitology (Parasite immunology). ? Spontaneouscure occurs when parasite establishes itself but is eventually expelled, ., Nippostrongylus brasiliensis (the rat hookworm). ? The adult Nippostrongylus, releases protective antigens that are not stage specific to the adult. That is, the resulting antibodies recognise targets both on the adult worm and on the migrating infective larvae. ? Under conditions of trickle infection, possible to get persistent population of parasites in gut which are able to survive the adverse immunological conditions. Morphologically though these worms are st