Gn allotypes in mother-father-cord trios. A selective transfer of autologous, fetal IgG to the mother.

When tested at a standard dilution (1:30), mother-cord Gm phenotypes are identical. A more sensitive assay reveals that the fetus does possess paternal antigen, that is, does produce small amounts of autologous IgG. The paternal antigens, in both the mother and the cord plasma, appear in a mosaic, one that suggests the fetus has the ability to selectively transfer his own IgG subclasses to the mother.