Identification of Blood Group Antigens and Minor Cell Populations by the Fluorescent Antibody Method

It is possible to produce fluorescence of erythrocytes as the result of specific antigen-antibody reactions of various blood group antigens; thus far, the factors A and B, a variety of Rh antigens and Kidd, have been successfully demonstrated with this method. It is important to realize that in the presence of adequate negative controls, low intensity fluorescence like that obtained with Rh antigens is nevertheless specific in systems involving erythrocytes.

The method discriminates between A₁ and A₂ cells. More antibody must be attached to the red cell for fluorescence than for agglutination. The relative paucity of antigenic sites of Rh substance as compared to A and B antigens is reflected by the difference in intensity of fluorescence.

The fluorescent antibody technic has been used successfully for the demonstration, and, to some extent, quantitation of minor cell populations in in vitro mixtures and in vivo. Injected Rh-positive erythrocytes were demonstrated in the blood of an Rh-negative volunteer during a period of 20 days. Fetal Rh-positive erythrocytes were demonstrated in several Rh-negative women, both with and without antibody, in the last trimester of gestation.