Immunoglobulin G subclasses and isoimmunized pregnancy outcome.

Immunoglobulin G antibodies are the most frequent type of red blood cell isoantibodies. They possess the ability to traverse the placenta and may cause hemolytic disease in newborn infants. Of the four subclasses, IgG1 and IgG3 are effective at binding erythrocytes to monocyte-macrophages and therefore are potentially destructive to erythrocytes. IgG2 and IgG4 are unable to react effectively with receptor sites on phagocytic cells and so are totally inactive relative to hemolysis. IgG subclasses were identified in 22 consecutive isoimmunized antepartum patients. Fifteen patients were subsequently delivered of babies who were either affected by or susceptible to hemolytic disease of the newborn. When maternal antibodies consisted of IgG1 only, hemolytic disease of the newborn developed in four of five cases. When only IgG3 was present, each of two patients developed hemolytic disease of the newborn. In eight cases both IgG1 and IgG3 were present and all the babies were born with hemolytic disease of the newborn. Determination of IgG subclasses might prove to be a useful adjunct in evaluating isoimmunized pregnancies. However, the limited information available does not permit the use of IgG subclasses exclusive of traditional means of diagnosis and management of isoimmunized pregnancies.