Major Histocompatibility Complex (MHC) Class II Antigen (HLA‐DR, DQ, and DP) Expression in Human Fetal Endocrine Organs and Gut

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Abstract
Monoclonal antibodies were used to analyse adrenal, pancreas, thyroid, and gut samples from human fetuses (14–11) weeks estimated gestational age; EGA) for the presence of class II major histocompatibility complex (MHC) antigens (HLA‐DR, DQ, DP) by immunohistochemistry. In the adrenal definitive and fetal cortex, HLA‐DR+, DP−, DQ− cells were clearly demonstrated. These DR+ cells were identified, phentotypically, as predominantly tissue macro‐phages and a small population of CD45R+, IgM+ lymphoid cells. Within the pancreas, numerous cell throughout the tissue were strongly DR+ but DQ−; DP+ cells were not observed until 17 weeks EGA. Using a double‐labelling procedure, minor proportions of these DR+ cells were identified as macrophages or as (CD19+) B cells, while endocrine and endothelial cells were negative. Throughout the thyroid, small numbers of DR+ macrophages and small lmyphoid cells were detected, although the thyroid epithelial cells were DR+, DP+, and DQ−. Large numbers of DR+, DP+, DQ− cells were observed in the stomach wall and mucosa. In the intestine, DR+, DP+, DQ+ cells positive for all MHC class II loci products were abundant throughout the lamina propria and lymphoid aggregates. The class II antigens appeared in the proportion DR>DF>DQ and expression was most prevalent in the mid‐gut region. A small proportion of epithelial cells of the villi along she gut were weakly DR+ but DQ−, DP−. These results show that DR+ cells in fetal endocrine tissue are mainly‘passenger leucocytes' and that, in contrast to recent reports concerning normal adult tissue, the adrenal and pancreatic endothelial cells are DR−.