Immunohistochemical Identification of Type B Intercalated Cells in the Rat Kidney by a Monoclonal Antibody.

Abstract

We recently produced monoclonal antibodies using macrophagic cells derived from cultured rat glomeruli as the antigen. One of the antibodies, named OS-3, was found to detect a cell population scattered in collecting ducts of the rat kidney as well as macrophages in various tissues. The present study deals with the cellular and subcellular localization of immunoreactivities with OS-3 in the kidney and other organs of rats. Double immunostaining using OS-3 and an anti-serum against either calbindin or epidermal cytokeratin showed that OS-3-immunoreactive cells exist exclusively in both the connecting segment and cortical collecting duct, and differ from calbindin- or cytokeratin-positive epithelial cells. Ultrastructurally, OS-3-immunoreactive cells appeared spherical in shape with few cytoplasmic microprojections on the narrow apical surface. Their relatively dark cytoplasm contained numerous mitochondria and a developed tubulo-vesicular system. The intense immunoreactivity was selectively localized in the basolateral membrane exhibiting shallow but complicated infoldings. Distribution and ultrastructural properties of the OS-3-immunoreactive cells showed that they were type B intercalated cells, which are engaged in the regulation of the acid-base balance mainly by secreting HCO3-. Another positive staining with OS-3 was found in the macula densa and some epithelial cells of Bowman's capsule, the former monitoring Cl- concentrations in the urine. Immunoblotting of extracts from the rat kidney demonstrated a protein band immunoreactive to OS-3 at a molecular weight of 43 kDa. Aside from the kidney, a specific and intense immunoreactivity with OS-3 was also found in the epithelial cells of the pancreatic excretory duct and in the secretory cells of the salivary, pyloric and duodenal glands, all of which are HCO3- -secreting cells. These immunohistochemical findings imply that OS-3 is useful for the detection of type B intercalated cells and recognizes a functional molecule involved in the production/secretion of HCO3- or transport of Cl-.