| BackgroundSchistosomiasis is a serious threat to the public health and remains a significant health problem worldwide at present. Rapid reinfection following treatment demands frequent retreatment, which makes the chemotherapy approach expensive and not easy to prevent reinfection. Moreover, some schistosome strains of praziquantel-resistant or decreased susceptibility to the drug have been observed recently in several countries. Therefore, it emphasizes the need for a more long-term approach. To develop a schistosomiasis vaccine may be one of cheap and efficacious approaches. As the use of sugar materials or molecules containing sugar (proteoglycans, glycoproteins and glycolipides) are the protective antigens of schistosoma, it is difficult to produce vaccines by the technique of genetic engineering. Anti-idiotypic antibody vaccines of schistosomiasis have aroused great attention.Guan xiao hong et al (1991) established a strain of monoclonal anti-idiotypic antibody NP30 of Schistosoma japonicum, which is an internal image anti-idiotypic antibody of gut associated antigen (GAA ), its antibody isotype is IgM. NP30 has a partial cross reaction with soluble egg antigen (SEA) and membrane associated antigen (MAA). NP30 molecule has been researched on many aspects. It has been confirmed that NP30 has sensitizing effect on formation of hepatic egg granulomasin mouse model for hepatic egg granuloma of Schistosoma japonicum; immunization with NP30 in Kunming mice, C57BL/6 mice ,BLB/c mice and goats obtained worm reduction of 50.46% , 41.67%, 39.53%and 42.78%, respectively. NP30 possesses effects of both anti-fecundity and anti-embryonation immunity on female worms of S. japonicum. Moreover, NP30 plays a significant down-modulatory role to hepatic granuloma and fibrosis. Anti-idiotypic antibody NP30 was confirmed with protective immunity of both anti-infection and anti-pathology and may act as a vaccine candidate for schistosomiasis japonica. But we didn't know the duration of the protective immunity induced by NP30 at present. This study was to see the duration and to find out the mechanism of the host protective immunity induced by NP30 at the basic of NP30 having been studied anciently. Objectives1. To know the duration of the protective immunity induced by NP30.2. To investigate the mechanism of the host protective immunity induced by NP30.Methods1. The 107 kunming mice were divided into two groups with active immunity. The test group was intraperitioneally injected with NP30 10 ug per mouse for three times every two weeks, while the control group was injected with 0.9% sodium chloride solution intraperitoneally. Each mouse was infected with 40 cercariae of S. japonium in the abdominal skin at the eighth, twelfth, sixteenth, twentieth, twenty-form week respectively after the third injection.2. Recovery of adult worms was carried out by left ventricular-portal perfusion at 6 weeks after challenge infection and hepatic tissue eggcounts were performed. The worm and egg reductions were calculated.3. The test of footpad in mice was conducted at the fortieth day after cercariae challenging.4. The mice serum was remained at two days before immunity, infection and killing. Serum specific IgG, IgG1, IgG2a antibody levels were analyzed by indirect enzyme-linked immunosorbent assay (ELISA).5. The concentrations of IFN- y and IL-4 in splenocyte culture supernatants(stimulated with NP30 for 72h) were quantified using a commercial ELISA kit according to the manufacturer' s instructions.6. The data were analyzed by SPSS 10.0. Comparisons of data were tested for significance with t test. P<0.05 was the significant level. Results1. The reduction rate of adult worms ranged from 21.43% to 41.16% and the reduction rate of eggs ranged from 26.15% to 63.67% at the eighth, twelfth, sixteenth week after the third immunity of NP30. There was significant difference in the reduction rate of adult worms and eggs at the eighth, twelfth, sixteenth week between the test group and the control...
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