STUDIES WITH MARKED ANTISERA. III. INTERCHANGE BETWEEN UNMARKED ANTIBODY AND I131-MARKED ANTIBODY IN COMBINATION WITH CELLULAR ANTIGENS.

Specific interchange takes place between 131I-marked antibody combined with cellular antigens and the free unmarked antiserum antibody in three systems studied: (A) bovine cells with (i) human infectious mononucleosis serum and (ii) rabbit anti-bovine serum and (B) human Rh D-positive cells with Rh incomplete anti-D serum. The rate of interchange is much slower than the initial combination of an unmarked antibody with an unoccupied antigenic site, and also is slower in the Rh incomplete system than in the other systems studied. Rabbit antibovine red cell antiserum partly interchanges with 131I-marked infectious antibody on bovine cells, but the reverse interaction does not apparently take place at all. Possible reasons are put forward to explain this. The infectious mononucleosis interchange reaction has a large temperature coefficient (about 4.9) which corresponds to a heat of reaction of 29,000 cal.