Immunohistochemical studies of the distribution of a basolateral-membrane protein in intestinal epithelial cells (GZ1-Ag) in rats using monoclonal antibodies

Summary The monoclonal antibody (mAb), GZ1, is specific for a 42-kilodalton (kD) protein (designated GZ1-Ag) present among the plasma membrane (PM) proteins of the absorptive cells of rat intestine. This protein only occurs in the basolateral PM and is absent from the microvillus membrane. GZ2 and GZ20 are two other mAbs that are also directed against GZ1-Ag but which specify other antigenic determinants of this protein than mAb GZ1. Used together, these three mAbs allow better characterization of GZ1-Ag and more precise investigation of its distribution and localization in various rat cells. We performed immunohistochemical labelling for GZ1-Ag at both the light-and electron-microscope levels and found that GZ1-Ag is extensively distributed in rat epithelial tissues. However, the amount of this protein present in epithelial tissue shows considerable variation. GZ1-Ag is not present in the secretory cells of terminal portions of most excretory glands or in cells of the endocrine glands and liver. The cells of kidney tubules, except for collecting tubules, also lack GZ1-Ag. Only small amounts of GZ1-Ag are present in the cells of the stratified squamous epithelium and transitional epithelium, the exception being superficial cells. High concentrations of GZ1-Ag occur in the excretory duct systems of glands and in the various kinds of epithelium present in the male and female genital tract. Our results also indicated that the GZ1-Ag in all of these cells has a very similar structure. In all cells, GZ1-Ag is localized in the PM, but it is present throughout the entire PM only in the cells of the stratified squamous epithelium and in the basal and intermediate cells of the transitional epithelium. In all epithelial cells bordering directly on the lumen, it is only present in the basolateral part of the PM, being absent from the luminal PM.