| Purpose of studyThis study was performed to determine the mucosal immune response following Toxoplasma gondii oral infection. We observed the responses of IgA antibodies in sera, intestinal secretions and proliferation of T lymphocyte subsets within gut mucosa-associated tissues in BALB/c mice. Materials and methodsSix- to 8-week-old BALB/c mice were used throughout the experiment and divided into two groups: control group, infected group. The ascites containing tachyzoites of RH strain of infected mice were gathered and adjusted to contain 5 104 tachyzoites in each 0.5-ml dose. The ascites were administered intragastrically to all animals of infected group by gavage while the control group was given PBS solution instead.Five mice in each group were killed per time-point on day 2, 4, 6, 8, 10, 13, 16, 19, 22, 25, respectively, after infection. The sera and intestinal secretions were gathered and the IgA antibodies in them were detected by ELISA; The Peyer's patches, mesenteric lymph node, intestinal mucosal epithelial tissues were prepared for the lymphocytes suspension and the changes of CD4+and CD8+ T cells in these sites were determined by SABC immunohistochemistry; The thymus and spleen were weighed and the numbers of the Peyer's patches were counted. Results and discussionThe level of IgA antibody in the sera and intestinal secretions were changed greatly. In the sera, IgA antibody persisted low until the 8th day post infection (pi), increased gradually, reached its maximum value on day 10 pi, then declined, but had tendency of increase around day 25 pi. Compare with the control group, the production in the sera was different on day 10, 25 pi. The IgA antibody in the intestinal secretions was much morethan that in the sera. They increased with the time after infection and reached the peak value on day 13 pi with a sudden decline on day 8. The antibody between the groups showed extraordinary difference on day 4, 6, 8, 13 pi.The subsets of T lymphocytes in the mucosal tissues showed great changes as the antibody. The CD4+ T subset of the mucosal inductive sites Peyer's patches was increasingly during the early stage of the infection, getting its highest level on day 8 pi and then decreased. The CD8+ T subset increased with no statistical difference. The two groups had significant difference on day 6, 8, 10 pi about the relative percentage of CD4+ and CD8+ T cells. For the mesenteric lymph node, there was no obvious change occurred. Intestinal epithelial had much more CD8+ T cells than other mucosal tissues. On day 6, 8, 10 pi we observed the significant increasing for the proliferation of CD8+ T cells while the CD4+ T subset of the mucosal effector sites didn't change greatly corresponding, so the CD4+: CD8+ ratio was reversed with significance. ConclusionDuring the period of infection in the BALB/c mice orally administered with toxoplasma, both humoral and cellular immune responses at the intestinal mucosal sites had taken effect. The IgA antibody in the intestinal secretions was the major effector at the local site as the first protective barrier defending the parasite. The time course of IgA production and its fluctuation were influenced by the strain virulence and the immunity properties of the mice.Besides the IgA antibody response, cellular immunity is also the important mechanism of local protection in toxoplasma infection, and different T cell subsets play efficient roles at different mucosal sites. CD4+ T cell subset in the inductive sites just like I'eyer s patches was increasing obviously, which indicated the parasite antigen processing. On the other hand, CD8+ T cell subset of the effector sites was activated and enhanced its cytotoxicity which was primary immune components when eliminating the parasite.
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