On the Blocking Antibody and the Zone Phenomenon in Human Anti-Rh Sera

Abstract

In 50% of Rh-mothers of erythro-blastotic infants, whose sera fail to agglutinate Rh-blood, antibodies are present which specifically coat the surface of Rh + red cells, making them resistant to potent anti-Rh agglutinins. These "blocking" antibodies agglutinate heavy suspensions of fresh blood but not washed blood in slide tests. Those anti-Rh sera which exhibit the so-called zone phenomenon contain both anti-Rh agglutinins and blocking antibodies, but the conc. of the former is greater. Some of these sera can be absorbed with Rh 4- blood, so that when the blocking antibody is removed the serum becomes a useful diagnostic agent. Anti-Rh sera exhibiting the zone phenomenon behave differently in specific absorption at 37 [degree] and at 0[degree]C. Without absorption tests it is difficult to state how often anti-Rh sera contain blocking antibodies and agglutinins. Agglutination is a manifestation of the blocking antibody per se. The characteristics of the agglutinating and blocking antibodies are sufficiently clear-cut so that, for example, there is no difficulty in the use of an anti-Rh serum which contains an anti-Rh agglutinin and also an anti-Rh blocking antibody.