Morphology, cytochemical features, and membrane phenotype of HLA-DR+ interstitial cells in the human pancreas.

The morphology, histological distribution, surface, and enzymatic phenotype of pancreatic HLA-DR+ cells were studied on seven human pancreata, removed from cadaver donors. Frozen and paraffin-embedded pancreas sections were stained with a battery of monoclonal antibodies by indirect immunofluorescence, immunoperoxidase, and immunophosphatase techniques. Two type of cells were found to express HLA-DR surface molecules: endothelial cells and nonfibroblastic non-B and non-T interstitial elements. The latter cells, which were localized both in the exocrine and endocrine portions of the organ, were distinguished in two main families (macrophagic and dendritic) according to their morphology, surface phenotype, and lysosomal enzymatic activities. The phenotype of cells belonging to macrophagic cell family was the following: Leu M1+, Leu M2+, Leu M3+, OKM1+, and OKT6-. In addition these cells were positive for the expression of lysosomal enzymes such as alpha-naphthyl acetate esterase (ANAE) and acid phosphatase (AP). The "dendritic" cell family comprised, among others, cells that were characterized by the presence of numerous finger-like projections, the absence of Leu M1, Leu M2, Leu M3, OKM1, OKT6 surface antigens, and by the negativity for ANAE and AP. These "dendritic looking cells" (DLC) constituted the most represented DR+ cell type within pancreatic islets. The demonstration of dendritic cells within human islets may justify, in humans also, in vitro procedures of intra-islet dendritic cell removal prior to transplantation, in the attempt of islet rejection prevention.