【正文】 ith termination of neuronal impulses via hydrolysis of acetylcholine at synapses and neuromuscular junctions. This unusual phenomenon has been known for some time, yet the physiological function of the enzymes remains undetermined. Helminth immune evasion strategies. Helminth immune evasion mechanisms in the invertebrate host. ? Anatomical seclusion – Acanthocephala acanthors maintain host tissue layer around them. Acanthor only bees melanised if developing larva dies. ? Molecular mimicry – sporocysts of Schistosoma in the intermediate moluscan host produce surface molecules that are similar 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。 Dirofilaria immitis suppress the immune response of the mosquito. Hymentopteran immune evasion strategies. Hymentopteran immune evasion mechanisms in the invertebrate host. ? Anatomical seclusion. Many parasitic wasps lay eggs in ventral ganglion of insect or spider hosts thus avoiding action of phagocytic cells. ? Immunosupression. Some parasitic ichneumonid wasps lay eggs in larvae of lepdopterans. Eggs are not attacked by the immune system as long as they stay alive . Nemeritis wasp lays eggs in the almond moth Ephesita. Evasion strategies of parasites of invertebrates. ? 1. Immature hosts. Many parasites take advantage of immature hosts in which there are less circulating haemocytes. ? 2. Incorporation of host antigen. This evasion strategy is used to make the parasite appear as “self” to the hosts? immune system. ? . The pedicellaria, tiny clawlike structures on surface of echinoderms. Used to prevent ectoparasites from settling. Mucous on the surface of these ?claws? inhibits the biting response. Many ectoparasites coat themselves in mucous to prevent being ?bitten? Evasion strategies of parasites of invertebrates. ? 2. Incorporation of host antigen cont’d. . Clown fish produce mucous that does not contain sialic acid, this prevents them being stung by tentacles of sea anemone with which it lives. However, lack of sialic acid makes the fish more susceptible to bacterial infections. Evasion strategies of ectoparasites of vertebrates. Ectoparasites also employ strategies to evade host defences amp。 whilst they are not immune evasion strategies they are worth briefly mentioning. ? Rapid feeding of bloodsucking insects to avoid host defensive movements. ? Use of ?hooks/claws? . claws on tarsi of head lice etc. used to hold on to hair – allows parasite to survive grooming activities of host. Summary. By the end of this session you should be: ? Familiar with vertebrate and invertebrate immune responses to different groups of parasites. ? Familiar with a range of strategies used by parasites to evade their hosts? immune mechanisms. ? Able to give examples of these parasites and link them to their immune evasion strategies. Next session. We will: ? Explore selected parasite immune evasion mechanisms in more detail. ? We will examine the immune evasion strategies of the schistosomes in both their intermediate and definitive hosts, Plasmodium, Trypanosoma cruzi amp。 the African trypanosomes.