Specific localization of macrophages in pregnant bovine caruncles

The objective of this study was to evaluate the distribution and phagocytotic function of macrophages in bovine caruncles during pregnancy. Pregnant Holstein caruncles obtained at a slaughterhouse and by Caesarean section just before the onset of parturition were used. Macrophages in these caruncles were observed immunohistochemically and histochemically. Macrophages were present in the parenchyma of caruncles throughout pregnancy. The macrophages were irregular in shape, and exhibited thin, long processes along the main and intermediate septa of caruncles. Macrophages increased as the gestation period progressed. Acid phosphatase activity of the macrophages appeared at 5-6 months of gestation and remained until the end of gestation period. In particular, macrophages showed strong acid phosphatase activity at the peripheral region of the caruncles just facing the chorionic villi. In addition, they were conglomerated in the hyperplastic prominences of caruncles. These results indicate that caruncle macrophages maintain the appropriate size and shape of each caruncle during pregnancy.