| Objective We observed the dynamic distribution in tissues of mice orally infected with Toxoplasma gondii tachyzoites for approaching the mechanism about toxoplasmosis,and observed the kinetics of IgA secreting cells in small intestine and the specific antibody level induced by Toxoplasma gondii in tachyzoite orally infected BALB/c mice to analysis the associativity between each other for investigating the possible contribution of IgA secreting cells during the mucosal immune response of resisting Toxoplasma gondii infection.This study was performed to observe intranasal immunization with STAg induced the kinetics of Toxoplasma gondii specific antibody secreting cells in small intestine and the specific antibody level in BALB/c mice for investigate the effect of IgASCs in different segment of small intestine mucosa by intranasal immunization with STAg during mucosal immune reaction against Toxoplasma gondii infection.Methods Twelve of 96 BALB/c mice were randomly selected intragastric administration with 0.5 ml PBS(control group),the rest of mice were intragastrically challenged with 1×10~4 tachyzoites of the virulent RH strain Toxoplasma gondii,twelve BALB/c mice of these mice were randomly sacrificed on the day 2,4,6,8,10,12 and 14 post infection,respectively.The distribution of tachyzoites in duodenum,jejunum,ileum,liver,spleen,kidney,lung,heart and brain in mice were tested under microscope by Giemsa's and Wright's stain.The quantitative change of IgA secreting cells(IgASCs) in mucosa of duodenum,jejunum and ileum were determined by immunohistochemistry analysis.IgG and IgA in serum and IgA in intestinal washes were detected by ELISA.Ninety-six 5- to 6-week old BALB/c mice were randomly divided into control group and immunity group.Mice were intranasally immunized with 20μg STAg per mouse twice at an internal of 2 weeks,while mice intranasally administrated with PBS were control.All mice were challenged intragastrically with 1×10~4 tachyzoites per mouse on day 7 after the last immunization.The incidence of mice were observed,Mice were killed by luxatioed certebrae colli on the day 6,7,8,9,10 and 11 post infection,eight mice each group between control group and immunity group once,respectively.The distribution of IgA secreting cells(IgASCs) in different segment of small intestine mucosa were determined by immunohistochemistry analysis.IgG and IgA in serum and IgA in intestinal washes were detected by ELISA.Results In duodenum,jejunum,ileum,lung and heart on day 2,in spleen on day 4,in kidney and liver on day 6,tachyzoites were detected,tachyzoites in brain were not found during the experimental stage.The quantity of tachyzoites in duodenum,jejunum,ileum increased gradually since the tachyzoites was detected,on day 6 post infection parasitic loads achieved a peak.The quantity of tachyzoites in liver was increased constantly since the tachyzoites were detected in mice.There were no difference about parasitic loads in kidney,lung and heart. Parasitic loads in spleen formed a peak on day 12.IgASCs were found in lamina propria of small intestine mucosa and the amount of IgA secreting cells varied differently from different location.The amount of IgASCs in duodenal mucosa upgraded gradually with the time of post infection went on.The amount of IgASCs in jejunal mucous membrane upgraded gradually from the day 2 to 8 post infection was degression whereafter until downgraded to the level of before infection at day 14.The amount of IgASCs in ileal mucous membrane upgraded gradually from the day 2 to 6 post infection was descended whereafter until downgraded to the lower level than that of before infection at day 12.The level of IgG in the sera and IgA in intestinal washes was increased continually and the IgA antibody in the sera was invariableness during the experiment phase.The associativity between the level of IgA in intestinal washes and the quantitative change of IgASCs in mucosa of duodenum, jejunum and ileum was r=0.732(P＜0.001),r=0.116(P=0.455) and r=-0.429(P＜0.005), respectively.The changeing regularity of IgASCs in small intestinal in mice after intranasal immunization with STAg as follow:the amount of IgASCs in duodenal mucosa increased gradually,in jejunal and in ileal mucous membrane upgraded incipiently and decreased subsequently with the time after infection;the amount of IgASCs on the day 11 were lower than that of the day 6 in ileal in control group,others were higher than those of the day 6;the amount of immunity group was higher than control group all the time,but no difference in statistics. The level of IgA in intestinal washes were degraded on the day 7,then increased slowly in immunity group and was equability in control group;the level of IgA in the sera upgraded incipiently and degraded subsequently following descending;the level of IgG in the sera was equability with the time after infection in two groups;the level of immunity group was higher than control group all the time,every index was no difference in its group but their difference was significant among groups in statistics(P＜0.05).Conclusion The results suggested that many tachyzoites were detected in small intestine tissues after peroral infection.Meanwhile small amounts of tachyzoites in lung and heart tissues were detected,and tachyzoites in spleen,kidney and liver detected tachyzoites on day 4 and 6 post infection.During the experimental stage parasite was not found in brain.The expression of the high-level IgASCs in duodenal and the heightening level of the specific IgA antibody in the intestinal washes induced by Toxoplasma gondii tachyzoites orally infected BALB/c mice,so positive correlation was shown between each other.The high-level IgA in the intestinal washes was secreted principally by duodenal.Intranasal immunization with STAg induced the expression of the high-level IgASCs in duodenal lamina propria and the heightening level of the specific IgA antibody in the sera and intestinal juice,indicated its function against Toxoplasma gondii infection.
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