Selective Localization of Factor VIII Antigenicity to Islet Endothelial Cells and Expression of Class II Antigens by Normal Human Pancreatic Ductal Epithelium

We evaluated the expression of factor VIII and class II histocompatibility antigens on frozen sections of normal human and rat pancreases. The immunohistologic studies were performed with directly fluoresceinated anti-human factor VIII and monoclonal antibodies A2B5, 3G5 (anti-islet), L-243, I-2, OK1 (anti-human Ia-DR), Leu-10 (anti-human HLA-DQ), anti-human HLA-DP, and OX6 (anti-rat Ia). Islet endothelial cells of humans and Wistar, CD, and BB diabetes-prone rats could be distinguished from intra-acinar endothelial cells by markedly enhanced factor VIII immunoreactivity. Factor VIII–antibody staining of islet endothelial cells was specifically absorbed by prior incubation of anti-human factor VIII antibody with normal human plasma but not by incubation with factor VIII–deficient plasma. By double indirect immunofluorescence, normal human pancreatic ductal epithelium expressed Ia in five of six pancreases studied.