Invasion and destruction of host cell Malaria, leishmaniasis, trypanosomiasis, Inflammation Trichnellosis, lymphatic filariasis, paragonimiasis, Amoebiasis, Chaga's disease and sleeping sickness Alergic manifestation Schistosomiasis, hydatid disease HOST IMMUNITY The host resistance or immunity in parasitic infections refers to the resistance offered by the host towards the injury caused by the parasites and their products. It may be classified into: a Innate, and b)Acquired immunity Innate immunity(先天性免疫) t is the inherited but non- immune type of the host defence against a parasite,eg, Haemoglobin- s thalassaemia(地中海贫血)andg! mucose-6- phosphate dehydrogenase(葡萄糖6-磷酸脱氢酶,G6PD) deficient erythrocytes(红细胞)are resistant against Plasmodium falciparum恶性疟原虫; persons with Duffy- negative genes(Dufy 阴性基因) are resistant to malaria,etc. Acquired immunity(获得性免疫) t may be a)Non- specific b)Specif. 1)Non-specific or acquired immunity It confers protective immunity against many elminthic infections. It is developed during exposure of persons to antigenically unrelated micro-organisms, microbial extracts or some sythetic products. Non-specific immunity has been shown to supplement the specific acquired immunity. These appear to be mediated by macrophages or their active products and also by interferons 2)Specific acquired immunity It is mediated by both humoral and cell mediated Immunities a) Humoral immunity It is mediated through the production of specific antibodies These antibodies are serum proteins and gamma globulins in nature. These antibodies may be protective or non-protective. The antibodies may offer protection in following ways O The antibodies prevent the parasites from attaching and penetrating the host cells by binding the specific sites on the surface of parasites the The antibodies neutralize parasite toxins and inactivate parasite enzymes by binding with determinants of parasitic antigens 8 The secretory IgA antibodies found in various body secretions prevent attachment of some protozoal parasites in the gut wall epithelium In a few parasitic infections(e.g, trypanosomiasis), the parasites are killed by lysis of antibody-coated cells mediated by the complement, and 6 The antibody dependent cell mediated cytotoxicity ADCC) helps in the killing of a few helminths coated by specific antibodies. It is an important mechanism by which the parasites are killed. This is mediated mainly by the lymphocytes and to some extent by neutrophils, eosinophils and macrophages. The antibodies are mainly of IgG, IgE and bind specifically to the parasites b)Cell mediated immunity (CMI) It is mediated through T cell which are cytotoxic. The CMI offers protection against many parasitic infections in following ways O Cytotoxic T lymphocytes alter the osmotic permeability of parasitic cells causing8 Invasion and destruction of host cell Malaria, leishmaniasis,trypanosomiasis, toxoplasmosis and amoebiasis Inflammation Trichnellosis, lymphatic filariasis, paragonimiasis, Amoebiasis Toxin Amoebiasis, Chaga’s disease and sleeping sickness Allergic manifestation Schistosomiasis, hydatid disease HOST IMMUNITY The host resistance or immunity in parasitic infections refers to the resistance offered by the host towards the injury caused by the parasites and their products. It may be classified into: a) Innate, and b) Acquired immunity. Innate immunity（先天性免疫） It is the inherited but non-immune type of the host defence against a parasite., e.g., Haemoglobin-S thalasaemia（地中海贫血） and glucose- 6- phosphate dehydrogenase （葡萄糖 6-磷酸脱氢酶，G6PD）deficient erythrocytes（红细胞） are resistant against Plasmodium falciparum 恶性疟原虫; persons with Duffy-negative genes（Duffy 阴性基因）are resistant to malaria, etc. Acquired immunity（获得性免疫） It may be a) Non-specific or acquired immunity, or b)Specific acquired immunity. 1) Non-specific or acquired immunity It confers protective immunity against many protozoal and helminthic infections. It is developed during exposure of persons to antigenically unrelated micro-organisms, microbial extracts or some sythetic products. Non-specific immunity has been shown to supplement the specific acquired immunity. These appear to be mediated by macrophages or their active products and also by interferons. 2) Specific acquired immunity It is mediated by both humoral and cell mediated immunities. a) Humoral immunity It is mediated through the production of specific antibodies. These antibodies are serum proteins and gamma globulins in nature. These antibodies may be protective or non-protective. The antibodies may offer protection in following ways: ① The antibodies prevent the parasites from attaching and penetrating the host cells by binding the specific sites on the surface of parasites. ② The antibodies neutralize parasite toxins and inactivate parasite enzymes by binding with the determinants of parasitic antigens. ③ The secretory IgA antibodies found in various body secretions prevent attachment of some protozoal parasites in the gut wall epithelium. ④ In a few parasitic infections(e.g., trypanosomiasis), the parasites are killed by lysis of antibody-coated cells mediated by the complement, and ⑤ The antibody dependent cell mediated cytotoxicity(ADCC) helps in the killing of a few helminths coated by specific antibodies. It is an important mechanism by which the parasites are killed. This is mediated mainly by the lymphocytes and to some extent by neutrophils, eosinophils and macrophages. The antibodies are mainly of IgG, IgE and bind specifically to the parasites. b) Cell mediated immunity(CMI) It is mediated through T cell which are cytotoxic. The CMI offers protection against many parasitic infections in following ways. ① Cytotoxic T lymphocytes alter the osmotic permeability of parasitic cells causing