Intraperitoneal Immunization with Cry1Ac Protoxin from Bacillus thuringiensis Provokes Upregulation of Fc-Gamma-II/and Fc-Gamma-III Receptors Associated with IgG in the Intestinal Epithelium of Mice

In humans, intestinal epithelial FcRn is expressed throughout life and mediates the bidirectional transport of IgG, but in mice, it is markedly expressed in neonatal intestine. In adults, its expression is only faintly upregulated after intestinal IgG induction such as that elicited by i.p. immunization with Cry1Ac protoxin (pCry1Ac) Bacillus thuringiensis. This led us to suggest that additional Fc receptors (Fc-R) may be participating in epithelial IgG uptake. So, first we determined whether CD16/32 [an epitope shared by Fc-RII (CD32) and Fc-RIII (CD16)] was expressed in the intestinal epithelia of mice. Using confocal microscopy and flow cytometry, we detected co-localization of IgG and CD16/32 in epithelial cells, whose frequency was increased by immunization with pCry1Ac. Western blot and cross-immunoprecipitation results with anti-CD16/32 and IgG antibodies in epithelial cell extracts suggested that epithelial cells bear both Fc-RII and Fc-RIII and contained IgG associated with Fc-RII/RIII. Using anti-CD32 and anti-CD16 antibodies, we confirmed by Western blot, confocal microscopy and flow cytometry that both Fc-RII and Fc-RIII were expressed and suggested that upregulation occurred upon immunization in intestinal epithelia. Finally, we examined the invitro effect of anti-CD16/32, anti-CD16 and anti-CD32 antibodies on IgG uptake and transport by intestinal epithelial cells and found that it was partially reduced. Although further studies are still required, our results suggest that Fc-RII and Fc-RIII might participate in the uptake and/or transport of IgG through the intestinal epithelia of adult mice.