Maternofetal transmission of IgG-bound hepatitis B e antigen

Abstract

Utilizing a highly sensitive radioimmunoassay, hepatitis B e antigen (HBeAg) was detected in the cord serum of eight out of nine babies born to mothers who carried hepatitis B surface antigen together with HBeAg. The titer of HBeAg in the cord serum was much lower than that in the corresponding maternal serum, and escaped the detection by the conventional micro-Ouch- terlony immunodiffusion. HBeAg in maternal and cord sera was fractionated into free and IgG-bound moieties by salt precipitation, and their proportion was compared in four pairs. In every pair tested, both free and IgG-bound HBeAg were found in the maternal serum, but only IgG-bound HBeAg was detected in the corresponding cord serum. Based on these results, IgG-bound HBeAg can be transmitted through the placenta, but free HBeAg may barely pass the placenta despite its much smaller size. Speculation: Among macromolecules present in the maternal circulation, only IgG is known to be transmitted into fetal circulation. The presence of IgG-bound HBeAg, but not of free HBeAg, in the cord serum of babies born to HBeAg-positive mothers suggests that IgG would be responsible for the maternofetal transmission of HBeAg. © 1982 International Pediatric Research Foundation, Inc.