Red cell destruction in vivo by low concentrations of IgG anti-A.

Red cells coated with as little as 0.3-0.5 mug anti-A/ML cells were found to agglutinate if mixed with plasma and rocked on a tile, whereas the minimum amount of IgG anti-Rh required for agglutination under these conditions was about 50 mug antibody/ml cells. Complement-binding by red cells coated with IgG anti-A could be demonstrated only when the amount of antibody on the cells was at least 14 mug antibody/ml cells. Since in ABO haemolytic disease the amount of antibody on the cells is frequently less than 0.6 mug/ml cells, it seems that red cell destruction in this syndrome is not due to the activation of complement but may be due to the sequestration of agglutinated cells. A few experiments are described in which the survival in vivo of small amounts of agglutinated cells was studied. Reasons are given for considering that such experiments fail to mimic the conditions prevailing in ABO haemolytic disease.