SPECIFICITY OF MACROGLOBULIN ANTIBODY SYNTHESIZED BY THE NORMAL HUMAN FETUS.

The umbilical cord blood of 47 out of 54 normal human infants contains hemagglutinating activity directed toward cells coated with a type-L Bence-Jones protein. This hemagglutinating material, in some instances, is present in cord blood in the absence of such activity in the maternal blood. Ultracentrifugation of cord serum in a sucrose gradient shows that the activity is associated with the macroglobulin fractions.