EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II ANTIGENS ON NORMAL PORCINE INTESTINAL ENDOTHELIUM

A novel monoclonal antibody (MIL 11) specific for an antigen expressed on porcine endothelial cells is described. The antigen recognized by MIL 11 is most strongly expressed in the intestine but is also express ed on the capillary endothelium of a wide range of tissues. Using two- and three colour immunofluorescence microscopy we demonstrated the ex tensive coexpression of MIL 11 and major histocompatibility complex (M HC) class II antigens on normal porcine capillary endothelium in the i ntestine, trachea, thymus and small veins, while endothelium of large vessels and the heart were negative for MHC class II. In contrast to h umans and rodents, available reagents do not detect MHC class II on th e intestinal epithlium of pigs. However, porcine intestinal endotheliu m expressed both DR and DQ antigens. A population of strongly class II -positive cells was also detected immediately adjacent to the endothel ium in the lamina propria. Three-colour immunofluorescence microscopy highlighted the close association between endothelium and intestinal C D4(+) T cells. Lamina propria T cells were mainly MHC class II positiv e, whereas those in the epithelial compartment were MHC class II negat ive.