Dendritic cells interact with CD4 T cells in intestinal mucosa

Absence of lymph nodes in nonmammalian species, ex-pression of MHCII by APCs in the periphery, and the re-cent findings that T cells can change their polarization status after presentation in the lymph nodes imply a role for MHCII-mediated presentation outside the orga-nized lymphoid tissue. This study shows that MHCII ECs and DCs from the intestinal mucosa of the pig can present antigen to T cells in vitro. In vivo, APCs colocal-ize with T cells in pig and mouse intestinal mucosa. In the pig, endothelium is involved in these interactions in neonates but not in adults, indicating different roles for stromal and professional APCs in the neonate com-pared with the adult. The ratio of expression of DQ and DR MHCII locus products was lower on ECs than on other mucosal APCs, indicating that the two types of cells present different peptide sets. Adult nonendothe-lial APCs expressed a higher ratio of DQ/DR than in ne-onates. These results suggest that mucosal DCs can present antigen locally to primed T cells and that stro-mal APCs are recruited to these interactions in some cases. This raises the possibility that local presentation may influence T cell responses at the effector stage af-ter initial presentation in the lymph node. J. Leukoc. Biol. 88: 571–578; 2010