Abstract
We have isolated a monoclonal antibody that was raised against rat mammary tumor cells. The antibody stains the lumenal edge of mammary duct epithelial cells. It immunoprecipitates a 200-kilodalton nonglycosylated, nonphosphorylated protein, which, by immunofluorescence and electron microscopy, can be localized in microvilli. In addition to microvilli of mammary ducts, this monoclonal antibody stains microvilli of the salivary ducts and of the renal nephron. It does not stain the microvilli of the intestinal brush border and shows a different tissue distribution than previously described proteins of this microvillus. We propose the name microvillin to distinguish the protein from other microvillar proteins. The presence of the protein distinguishes two classes of microvilli that are present in cells with possibly different transport functions.