Localization and origin at rat intestinal cholesterol esterase determined by immunocytochemistry.

Monospecific rabbit antisera to rat pancreas cholesterol esterase were employed in the unlabeled antibody enzyme method of immunocytochemistry in combination with the horseradish peroxidase--antihorseradish peroxidase complex to localize this pancreatic enzyme within the wall of rat small intestine. Intestinal rings were fixed in paraformaldehyde with satisfactory preservation of structure and retention of cholesterol esterase antigenic determinants. Fixed sections, 6 micrometers thick, were stained. In the light microscope, specific reaction product, represented by intense brown areas, was uniformly distributed within the absorptive cells but was notably absent from the microvillar membrane. Reaction product was also seen within the laminapropria and submucosa. In contrast, reaction product was absent from sections of proximal intestine surgically deprived of pancreatic juice for 72 hours. Furthermore, the intensity of staining in sections of normal intestine decreased with increasing distance from the pancreatic duct. These observations support the concept that "intestinal" cholesterol esterase is of pancreatic origin. This enzyme is localized within the cells as opposed to the absorptive surface.