Objective: To investigate the kinetics of IgA secreting cells (IgASCs) and secretory IgA (sIgA) level in small intestine induced by intranasal immunization with Toxoplasma gondii soluble tachyzoite antigen (STAg) in mice.
Methods: Ninety-six 5 to 6-week old BALB/c mice were randomly divided into immunity and control groups. Mice of the immunity group were each intranasally immunized with STAg 20 microg in 20 microl PBS, twice at an interval of 2 weeks, while the control mice were each given 20 microl PBS. All mice were challenged intragastrically with 1 x 10(4) tachyzoites in 0.5 ml per mouse in 1 week after the last immunization. The body weight and infection incidence of mice were recorded. Eight mice of each group were sacrificed on the day 6, 7, 8, 9, 10 and 11 post infection, respectively. The quantity of IgASCs in mucosa of duodenum, jejunum and ileum was detected by immunohistochemistry. The sIgA in intestinal washes were determined by ELISA.
Results: All mice fell ill post infection, but the symptom of mice in the immunity group was milder, the increasing level of body weight of mice in the immunity group was higher considerably than that in the control group (P < 0.05). Two mice died in control group on the 7th day after infection. sIgA level in intestinal washes increased continually in two groups, but the increasing level in the immunity group was higher than that of the control (P < 0.05). The number of IgASCs in duodenum increased slightly in the control group, but increased continuously and maintained a high level after 9 d in the immunity group, for instance, 20.65 +/- 1.67 in the immunity group and 12.30 +/- 2.67 in the control. The correlation of the sIgA level in intestinal washes and the quantitative change of IgASCs in duodenum was positive in the immunity group (r = 0.566, P < 0.05) and the control (r = 0.378, P < 0.05). The number of IgASCs in jejunum decreased in the control group but increased then slightly decreased after 9 d in the immunity group. Positive correlation between the sIgA level in intestinal washes and the quantitative change of IgASCs in jejunum was found in the immunity group (r = 0.218, P > 0.05) but negative in the control (r = -0.557, P < 0.05). The number of IgASCs in ileum declined in the control group but maintained a high level in the immunity group. The correlation between the sIgA level in intestinal washes and the quantitative change of IgASCs in ileum was r = -0.053 (P > 0.05) in the immunity group and r = -0.685 (P < 0.05) in the control.
Conclusion: Intranasal immunization with STAg in mice orally infected with Toxoplasma gondii can increase the number of IgASCs in jejunum and ileum, and enhance the immune barrier function of mucosa in small intestine of mice.