| A national survey reported in 2003 showed that the schistosomiasisjaponica was still a serious threat to public health, though medicalprogress has been achived in the recent years in China. There are morethan 800,000 patients and 100,000,000 people at risk.The useful therapies nowadays for controlling schistosomiasis arebased on the population chemotherapy with praziquentel, combined withpropaganda of health and killing snails in endemic areas, which haveattained great achievements. However, the achievement of controlprogram is being challenged by the high ratio of reinfection afterchemotherapy and drug resistant strains. In 1980s the worldwidescientists reached consensus that, it is a priority to develop an effectiveanti-schistosomiasis vaccine to prevent reinfection after chemotherapy.The research on the vaccine for schistosomiasis from the deadvaccine, live attenuated vaccine, engineering vaccine, to nucleic acidvaccine in the past seventy years. The following results are found:attenuated cercariae(AC) or schistosomulum induced much higher levelof protection in various animal models than any other candidate antigens.Neverthless, in practice, considering the production of AC, safety andsome ethical problems, AC is not practical enough to be used. However, the researchers hope to ascertain its immunological mechanisms to helpdefine novel strategies to vaccine design.Biological studies on AC inducing protection, such as exteriormorphous, interior microstructure, antigens and its allocation, are limited.The mechanisms may be related with different antigen presentationbetween AC and normal cercariae(NC) because of the radiation, whichconcerned with the delayed pattern of migration of AC, the alteration ofantigen presenting on the surface of the parasite (certain cryptic antigensexposured), and the ablation of certain proteins presenting on the NC thatfunction to down-regulate immune responses. Thus, exploring thebiological study of the attenuated cercariae, will help the protectionresearch to the next step.During the past decades, vaccine and its fundamental immunologicalresearches were mainly on Schistosomiasis mansoni, and found that, ACinduced 60%-80% protection in many species of mouse model,γ-irradiated AC could induce higher than 50% protection in primate. Butthe studies of Schistosomiasis japonicum were limited and mainly basedon the research of Schistosomiasis mansoni. Compared with Schistosomamansoni(S.m), the levels of protection in mouse induced by Schistosomajaponicum(S.j) AC were variable, and a good mice model is still absent inthe studies of S.j AC. Our lab has done the protection research using S.jAC in the mice model ofKM, DBA and C57BL/6, expecting to constructmice model suiting for S.j AC. Although humoral response induced by S.jAC was higher than NC done, the results were not as good as expected. Inthis study, we further defined the protective immunity in different micemodels, and compared the Th1/Th2 cellular responses in DBA group, inorder to study the relationship among mice species, immune responsesand the resistance to infection of S.j.Thus, in our study, we first observed the vigor of AC and NC, andthen systematically observed the difference of exterior morphous, interion microstructure, antigens and allocation between AC and NC usingscanning electron microscope(SEM), transmission electronmicroscope(TEM) and immune electron microscope(IEM).In order to construct a mouse model to be suiting for the studiesabout S.j AC and explore the immune response induced by S.j AC in host.We observed the protection induced by cercariae attenuated with differentintensity and sources of UV in KM mice. Base on these, we compared theprotection in different mice strains (KM, DBA, BALB/c), andinvestigated the the dynamic change of cellular immune response levelsinduced by S.j AC in hosts serum.The main results are as follows:1. The vigor of the cercariae: the mortality rate of the cercariae inducedby radiation with different UV intensity (200, 445(40秒), 800μw/cm~2were respectively 1.78%, 1.73% and 2.09%. There were no significantdifferences in mortality rate.2. Electron microscopic observation of the surface and internal sturctureof cercariae: compared with NC, the morphological features of ACwere①tight constrictions distributed along the length of the body,swelled furcae, depressed body, defected tegumental spine, and crudeedge;②The layer of muscle fiber became thiner and some fractured,cristae in mitochondria became swelled and disrupted and/or lost;③the quantity of the gold granules in the slice of AC were fewer than theslice of NC, especially in muscle layer, and congregated in multiplesites. The above indicated that radiation had affected the surface,muscle, structure of important metabolic organ, and antigen of thecercariae.3. KM, DBA, and BALB/c were the low responder mice to the S.j AC.The worm reduction rates induced by cercariae attenuated withdifferent UV intensity and sources in KM mice were -1.0～23.75%;8.13%, 18.59% and 26.49% worm reduction were induced in different mice strains (KM, DBA, and BALB/c) respectively through dosagesof 100 AC/mouse vaccination and 4 weeks time interval. The resultswere consistent with the former outcome in our lab, which indicatedKM, DBA, BALB/c and C57BL/6 are not suitable for studing theprotective immunity induced by S.j AC.4. Using Bio-plex liquid protein suspension array system, IFN-γ, IL-4,IL-12p40 and IL-10 were detected in the serum of DBA. It showedthat after using AC immuned, the expression of IL-12p40 decreasedlowest, but there were not significant differences between 0-4wk.Compared with samples from infected mice and infected afterimmuned mice, the level of cytokines sustained at relatively lowerlevel, while there were not significant differences over the time coursein the three groups (P＞0.05), the level of IL-12p40 from immunedgroup were respectively higher than infected group and infected afterimmuned group(P＜0.05); Compared the level of four cytokines frominfected group and infected after immuned group, there were notsignificant differences. It was indicated that the mice immuned withS.j AC could not induced valid cellular immune response, and thismaybe the main reason of could not induce higher protectiveimmunity by S.j AC.The results further enriched the study of protective immunity, andprovide useful strategies to the construction of animal model that suitingfor studing the protective immunity induced by S.j AC.
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