Participation of the spleen in the IgA immune response in the gut

The role of the spleen in the induction of an immune response to orally administered antigens is still under discussion. Although it is well known that after oral antigen administration specific germinal centres are not only formed in the Peyers patches (PP) and the mesenteric lymph nodes (mLN) but also in the spleen, there is still a lack of functional data showing a direct involvement of splenic B cells in an IgA immune response in the gut. In addition, after removal of mLN a high level of IgA+ B cells was observed in the gut. Therefore, in this study we analysed the role of the spleen in the induction of IgA+ B cells in the gut after mice were orally challenged with antigens. Here we have shown that antigen specific splenic IgM+ B cells after in vitro antigen stimulation as well as oral immunisation of donor mice were able to migrate into the gut of recipient mice, where they predominantly switch to IgA+ plasma cells. Furthermore, stimulation of recipient mice by orally administered antigens enhanced the migration of the splenic B cells into the gut as well as their switch to IgA+ plasma cells. Removal of the mLN led to a higher activation level of the splenic B cells. Altogether, our results imply that splenic IgM+ B cells migrate in the intestinal lamina propria, where they differentiate into IgA+ plasma cells and subsequently proliferate. In conclusion, we demonstrated that the spleen plays a major role in the gut immune response serving as a reservoir of immune cells that migrate to the site of antigen entrance.