Intrauterine Isoimmunization caused by Maternal IgA crossing the Placenta

Abstract

THE IgG of the neonatal human infant is almost entirely derived by selective transplacental passage of maternal IgG, but IgA and IgM are considered incapable of transplacental passage. In spite of immunological immaturity, the human foetus has been shown to produce antibodies, predominantly IgM, in response to various bacterial and viral antigens^1,2. The very low level of IgM detectable at birth is of foetal origin¹. IgA is synthesized by the foetus in exceedingly limited amounts, for only very low concentrations of IgA in cord serum have been detected by highly sensitive techniques. Nonetheless, small amounts must be synthesized by the foetus because immunization of pregnant women to IgA is not infrequent. We have observed that about 15 per cent of the mothers of recently delivered babies have antibody to IgA (anti-IgA) detectable in their sera (unpublished observations). Similarly, Cassidy et al. have also observed anti-IgA in sera of women who have never received parenteral injection of IgA in the form of blood or blood products³. Such antibodies may be directed against the allotypic antigens of IgA.