[Blood groups A and O with a weaker serological reactivity to agglutinins in the serum].

In normal conditions anti-A and anti-B agglutinins are seldom weak and very seldom they are completely absent. Agglutination reaction depends on temperature. It is intensified by treatment of erythrocytes with enzymes (papain) and is also dependent on genotype of the person investigated. Alterations are more frequently observed in anti-B agglutinin. Two cases with defective A and O blood groups are presented, with anti-B agglutinin missing at routine investigation. Treatment of erythrocytes at 4 degrees C with papain indicated the presence of anti-B agglutinin which has a weaker serological expression. Assessment of immunoglobulin concentration by laser nephelometry before and after adsorption and elution, also indicated the presence of this agglutinin.