Placental alkaline phosphatase types and transplacental IgG transport

Recently, results have been presented which suggest that placental alkaline phosphatase (PLAP) is an IgG receptor, and that the transplacental transport of IgG from mother to fetus is dependent on the fetal PLAP genotype. In order to confirm the relationship between the PLAP types and transplacental IgG transport, we studied fetal (cord serum) IgG levels in relation to PLAP types, quantitative variations in PLAP activity, maternal IgG levels and gestation length. Fetal IgG levels and the fetal/maternal IgG ratio showed no significant correlation with PLAP types and PLAP activity. Thus differences between PLAP types with respect to transplacental IgG transport are unlikely to play a selective role in the maintenance of the PLAP polymorphism. In accordance with results from previous studies, significant correlations were found with maternal IgG levels and gestation length. Perusal of the literature suggests that PLAP is mainly an IgG1 receptor.