Lack of relation between expression of HLA-DR and secretory component (SC) in follicle-associated epithelium of human Peyer's patches.

Follicle-associated epithelium (FAE) of normal human Peyer's patches (PP) was studied with regard to expression of HLA-DR determinants and secretory component (SC); the latter acts as a receptor for polymeric immunoglobulins (pIg). Putative M cells were identified in FAE by lack of a brush border with alkaline phosphatase. These cells were virtually negative for HLA-DR whereas the remaining FAE was strongly positive like villous epithelium. Conversely, the complete FAE showed no SC expression and was negative for IgA. These findings suggested that the FAE (including the M cells) does not participate in SC-mediated transport of pIgA, which in the gut mainly takes place through columnar crypt cells. The FAE (excepting the M cells) may be involved in an MHC class II-restricted antigen-presenting function as recently suggested for villous epithelium. The role of M cells may hence be limited to uptake and transport of luminal antigens.