Visualization of peptide presentation following oral application of antigen in normal and Peyer's patches‐deficient mice

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Abstract
Orally applied antigens generate systemic unresponsiveness by induction of anergy and deletion of specific T cells at high antigen doses, and induction of regulatory T cells at low doses of antigen. These different immune reactions have been attributed to different types of antigen‐presenting cells (APC) and/or different secondary lymphoid organs participating in the induction of the immune response. We used high‐sensitivity immunofluorescence to directly identify for the first time the cells presenting orally applied antigen in vivo. At low peptide doses (1 mg) peptides were presented systemically and by all types of APC but presentation was still maximal on DC of the PP (up to 65%). Nevertheless, at limiting antigen doses T cell activation in the gut‐associated lymphoid tissue occurs preferentially in the mLN but not in PP. PP‐deficient mice have the same frequencies of peptide‐presenting cells in mLN, peripheral lymph nodes and spleen and activation of naive T cells in vivo is not affected. Therefore, PP are not critical for antigen presentation as well as for T cell activation in response to orally applied soluble antigens.