Immunofluorescent staining of histaminase (diamine oxidase) in human placenta

An immunofluorescent procedure for the localization of histaminase in human tissue sections has been developed by using a specific antiserum against human placental histaminase. For localization of this enzyme in placental sections, fixation in equal volumes mixture of absolute ethanol and acetone provided the optimum visualization of this enzyme in both frozen sections and paraffin-embedded sections. The immunofluorescent staining of this enzyme in placenta is found to be localized in areas within the maternal decidua, both within the cytoplasm of the decidual cells and in tissue space between the cells. The chorionic villi are completely void of the immunofluorescent stain. Variations in patterns of histaminase localization have been found between term and premature placentas, with the former showing a predominantly intercellular localization and the latter a predominantly intracellular localization. The intercellular localization of this enzyme in the decidua may represent a nonspecific diffusion of the enzyme associated with delivery of the placenta or may reflex a specific functional role of the enzyme in the intercellular space during pregnancy.