Immunocytochemical characterization of the pancreatic islet cells of the nile tilapia (Oreochromis niloticus)

The cellular composition and topography of the pancreatic islet of Oreochro mis niloticus, now known to be a donor source for islet xenotransplantation studies, were characterized. Whole tilapia islets were harvested using an enzymatic method and then further digested into single-cell preparations. C ell cytospin preparations of islet cells and paraffin sections of whole isl ets were stained using antisera against tilapia insulin, human glucagon, sa lmon somatostatin-25 (SST-25), human somatostatin-14 (SST-14), and salmon p eptide tyrosine-tyrosine (PYY) using the immunoperoxidase method. Cell coun ts, performed on cytospin preparations using a Quantimet 570 computerized i mage analysis system, revealed that O. niloticus islets contained 78% endoc rine cells and 22% immunonegative cells (i.e., mainly nucleated erythrocyte s and rare tissue eosinophils). The proportions of immunopositive endocrine cell types were: 42.3% insulin immunopositive cells, 11.5% glucagon immuno positive cells, 23.1% SST-25 immunopositive cells, 21.8% SST-14 immunoposit ive cells, and 1.3% PW immunopositive cells. Islet cell topography was eval uated using histologic sections of whole endocrine pancreata including larg e, medium, and small islets. Round to Polygonal insulin immunopositive cell s with round central nuclei were distributed in clusters throughout both th e principal and the smaller islets. Elongate SST-14 immunopositive cells we re closely associated with the clusters of insulin immunopositive cells; bo th were surrounded by SST-25 immunopositive cells, which were similar in sh ape to the insulin immunopositive cells. There were elongate glucagon immun opositive cells throughout the islets, whereas the PW immunopositive cells were restricted to the periphery and to channels of fibrovascular connectiv e tissue penetrating the islets. (C) 1999 Academic Press.