Lysosomal enzyme secretion from human placental villi is increased by serum albumin and IgG

Human serum albumin and IgG increased the secretion of the lysosomal enzyme, β-hexosaminidase, from human placental villi in a dose- and time-dependent manner. Release was also enhanced by bovine serum albumin and ovalbumin. β-Hexosaminidase secretion was not increased by the non-endocytosable substrate, IgG-Sepharose, indicating that the signal for release is not given by the interaction of protein with the cell surface. Experiments with ¹²⁵I-labelled albumin and IgG showed that both proteins were actively internalised by placental villi giving credence to the idea that secretion is triggered after uptake.