Distribution of Ca (Oxford) antigen on placental trophoblast

The distribution of the Ca (Oxford) antigen in 75 human placentae has been studied using an immunohistological technique. The antigen was not detected until nineteen weeks gestation, when it first appeared on the surface of syncytial sprouts. Thereafter it spread to the syncytiotrophoblast of chorionic villi of all sizes, becoming more strongly expressed towards term. The antigen was consistently not detected on extravillous trophoblast. The significance of these findings is discussed in relation to competing theories as to its function.