| At present, one of the most important challenges to the population of an endemic area with Schistosomiasis japonica is that reinfection is very difficult to control. There is a high priority for the development of effective anti-schistosomiasis vaccines. Therefore, host immune response to infection with schistosome is an important topic.Host can produce protective immunity against schistosomes, which is also called "Acquired Immunity". In rat, primate and human schistosomiasis, it is widely agreed that the mechanism of antibody-dependent, cell-mediated cytotoxicity (ADCC) plays a major role in the expression of acquired resistance, associated with elevated immunoglobulin E (IgE) concentrations and blood and tissue eosinophilia.A major conceptual revolution in immunology by dividing mouse T helper cells into two populations with contrasting and cross-regulating cytokine profiles, deeply influenced our understanding of the immunity to schistosomes infection in human populations and in experimental models. In mice infected with Schistosoma mansoni, Th1 response characterized by antibody-independent macrophage activation is predominant. Same phenomenon is also observed in the population of S. mansoni and S. haematobia-endemic areas. Schistosome specific IFN- r is significantly higher in people with acquired resistance. IFN- Y can up-regulate IgE receptor on the membrane of platelet to reinforce ADCC effect, and induce the expression of some effector molecules, such as NOS, TNF- a , some chemokines. In contrast, it is universally accepted that in hurnans, primates and rats, protective immunity to schistosomes is associated with Th2responses (IL-4, IL-5, IgE, IgG4 and eosinophils). The importance of Th2-type responses in resistance is supported further by the identification from human genetic studies of a "resistance" gene, mapping with the "Th2-cluster" genes, including IL-5, IL-13, etc. on chromosome 5q31-q33. IgE responses and eosinophils in schistosomiasis and their role in protective immunity have to be regarded as part of a Th2-dependent regulatory circuit.The immune response to S. japonicum infection has its own characteristic. Firstly, immunoepidemiological data provided evidences that human acquire age-dependent resistance to reinfection by schistosomes. Compared with S. mansoni and S. haematobium infection, acquisition of anti-S.japonicum infection resistance develops more slowly and lasts shorter. Secondly, IgE antibody, one of the important components mediating ADCC effect, has been correlated with the development of resistance to reinfection for both S. mansoni and S. haematobium. But it is not clear if the age-dependent increase of IgE antibody in people from S. japonicum-endemic area correlates with resistance. It is possible IgE antibody binding allergens mediates anaphylaxis to S. japonicum. Thirdly, the exact role played by cytokines in regulating susceptibility or resistance to S. japonicum infection in humans remains unclear. Our preliminary studies in an endemic area of S.japonicum, the PoYang Lake area, Jiangxi province, suggested that the cell-mediated immune response of the human population was down-regulated in general, but no significant difference was shown in Th1 or Th2 subset, especially in egg positive individuals.The differences of immune response to schistosome infection observed in different hosts and even sometimes in the same host, indicate that the complex interaction between host and parasite can't simply be restricted to the context of Thl and Th2 cells and the effects of their products. It is likely that the expression of immunity against schistosomes is the result of the combination and appropriate balance of cytokines and effector cells.Researchers on immunity to schistosomes has thrown up ideas which, at their inception, appeared to provide promising routes to an effectivevaccine. With the development of molecular biology, a number of the S. japonicum specific antigens have been cloned and characterized. Up to now, their protective efficiency does not r...
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