Professional and non-professional antigen-presenting cells in the porcine small intestine.

We have previously presented evidence of a highly organized and compartmentalized structure of the small intestinal lamina propria of the pig. In this work, we have identified at least two major populations of cells in this site expressing high levels of major histocompatibility complex (MHC) class II antigens. One is CD45 positive and is a potent initiator of a primary immune response, this is a function usually associated with dendritic cells. These cells have characteristic dendritic morphology, but show evidence of phagocytosis as well as other phenotypic markers of immature dendritic cells. Some cells show evidence of ongoing immune maturation. We have also isolated CD45 negative endothelial cells bearing significant amounts of MHC class II, which do not trigger a mixed lymphocyte reaction. These findings have implications for the functional role of healthy gut lamina propria and clearly implicate this site as capable of differential antigen presentation by a heterogeneous population of antigen-presenting cells.