Immunization with Cry1Ac from Bacillus thuringiensis increases intestinal IgG response and induces the expression of FcRn in the intestinal epithelium of adult mice.

We have shown that Cry1Ac protoxin from Bacillus thuringiensis is a potent mucosal and systemic immunogen with adjuvant properties. Interestingly, we have observed that Cry1Ac preferentially induces high specific IgG responses in intestinal fluid when it is intraperitoneally administered to mice; therefore, in the present study, we used this protocol, as a model to address the influence of systemic immunization on the induction of the intestinal IgG response. The data shown indicate that upon intraperitoneal immunization with Cry1Ac, significant intestinal specific IgG cell responses were produced in the lamina propria, accompanied by an increased frequency of intestinal IgG+ lymphocytes and epithelial cells containing IgG. Considering that FcRn is the receptor responsible for the transport of IgG in neonatal intestinal epithelia, but it is developmentally downregulated in the rodent intestine, we analysed whether upon intestinal IgG induction, FcRn mRNA expression was induced in intestinal epithelial cells, of adult mice. Whereas in intestinal epithelia of unimmunized adult mice FcRn mRNA was not detected, in Cry1Ac immunized mice it was expressed, although the level was lower in comparison with that found in neonatal epithelia. Then using flow cytometry and immunofluorescence we confirmed that the expression of the protein FcRn was induced in the intestines of adult immunized mice especially in the large intestine. Finally, we found that Cry1Ac also increased FcRn expression in isolated intestinal epithelial cells stimulated in vitro. The outcomes suggest that the expression of FcRn in intestinal epithelium might be reactivated upon immunization, and possibly facilitate IgG transport.