Identification of cell types containing S-100b protein-like immunoreactivity in the islets of Langerhans of the guinea pig pancreas with light and electron microscopy.

Cell types containing S-100b protein-like immunoreactivity in the islets of Langerhans of the guinea pig were studied by light- and electron-microscopic immunocytochemistry using antisera to S-100b protein, insulin, glicentin, somatostatin, and pancreatic polypeptide. Two types of S-100b-immunoreactive cells were identified. The first type was stellate and characterized by thin cytoplasmic processes sheathing endocrine-type cells, especially pancreatic A-cells. It was located predominantly in the neuro-insular complex and in large islets, both of which were located near the main pancreatic duct. Intense immunoreactivity was found in the cytoplasmic matrix as well as in the nucleoplasm. Nerve fibers or endings were occasionally ensheathed by its cytoplasmic processes. The second type, whose immunoreactivity was rather weak and varied from one cell to another, was oval to polygonal in shape and located randomly throughout the islets. It was an endocrine cell-type and its immunoreactivity was located in the secretory granule. With the use of immunostained consecutive sections for demonstrating pancreatic endocrine cell-types, it was found that a portion of the pancreatic B-cell population expressed S-100b-like immunoreactivity.