Hemagglutinating antibodies to grass in maternal and cord sera

Twelve of 24 sera from nonimmunized atopic mothers at delivery contained hemagglutinating antibody to ryegrass, but no cord sera contained this. Naturally occurring hemagglutinating antibody did not pass through the placenta in demonstrable quantities. In two nonatopic and two atopic mothers immunized with mixed grass during pregnancy, maternal and cord sera contained hemagglutinating activity in equal titers. Artificially induced hemagglutinating antibody passed freely through the placenta. None of the sera obtained from 58 nonatopic mother-cord pairs contained hemagglutinating antibody. Since hemagglutinating antibody to ryegrass in the nonimmunized individual does not cross the placenta, it is probably associated withγ 1A - orγ 1M -globulin