| At present, one of the most important challenges to the population living in an endemic area with schistosomiasis japonica is the long-term persistence of pathogen in the host and no strong protective immunity. Thus, reinfection is difficult to be resisted. Studies in human populations and experimental models showed that the specific host immunity to schistosome is gradually down-regulated with the development of schistosomiasis, which is similar to other chronic infections, including tuberculosis and leishmaniasis. Recently, growing evidences have been presented to support the association between the chronic infections and CD4+CD25+ regulatory T cells. But to date, most data concentrated on the role of CD4+CD25+regulatory T cells in autoimmunity diseases while the functions of these cells in schistosomiasis japonica are unclear. Our study focused on the role of CD4+CD25+regulatory T cells during S.japonicum chronic infection.We established BALB/c mice model infected with S.japonicum. To examine whether CD4+CD25+regulatory T cells contribute to the suppression of immune response, we separated CD4+CD25+ regulatory T cells from the mice lymphatic nodes and spleens using magnetic beads. The other immunocytes were isolated by removing CD4+CD25+ regulatory T cells, which were co-cultured with or without CD4+CD25+ regulatory T cells. The inhibitory function of CD4+CD25+regulatory T cells was assessed by the [3H] thymidine incorporation method with the stimulation of ConA or SEA. Then, at a serial of time points post infection, we measured the percentage ofCD4+CD25+regulatory T cells from mesenteric lymph nodes and spleens by flow cytometry. The gene expression of CD25 and Foxp3 in CD4+T mRNA was analyzed using quantitative real-time PCR and the gene expression of cytotoxic T lymphocyte -associated antigen 4 (CTLA-4) was acquired by general RT-PCR. All the infected mice have their normal controls respectively.The main results we got are as follows:1. Functional assays revealed CD4+CD25+ regulatory T cells from chronic infected mice inhibited the proliferation of the other immunocytes. CD4+CD25+ regulatory T cells from both the infected and normal mice have suppressive effects on the responses of immunocytes (without CD4+CD25+regulatory T cells) to ConA stimulation. However, with the specific antigen SEA stimulation, 65% inhibition was observed when the immune cells were co-incubated with CD4+CD25+regulatory T cells from chronic infected mice. But 20% inhibition occurred in normal control experiment. Weak inhibitory capacity was shown without antigen stimulation. And CD4+CD25+ regulatory T cells itself displayed little proliferation whether or not with antigen existence. These results suggested that the inhibitory properties of CD4+CD25+ T cells were activated with the persistent stimulation of SEA, and CD4+CD25+ regulatory T cells played a crucial role in the immune response resistance during S.japonicum chronic infection.2. During the chronic infection of S.japonicum, the percentages of CD4+CD25+ regulatory T cells in immunocytes or CD4+T cells from lymph nodes and spleens was elevated and the expression of gene CD25 was increased. In the acute stage of infection, the percentage of CD4+CD25+ regulatory T cells was decreased to low level, and up till chronic stage the ratios were higher than before, though CD4+CD25+ regulatory T cells/CD4+T cells rebound to or even higher than control. The expression of gene CD25 escalated during the course of the infection. We speculated active CD4+CD25+ regulatory T cells suppressed the proliferation of the inflammatory cells, and /or the increasing CD4+CD25+ regulatory T cells is correlated with higher expression of CD25 gene.3. During the chronic infection of S.japonicum, the mRNA of transfer factor Foxp3 gene increased in CD4+ T cells from mice lymph nodes and spleens. From acute stage, the expression of foxp3 began to elevate and till chronic stage it was significantly higher than the control groups. Foxp3 is on... |
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