[An acquired B antigen in a subject of A2 group].

Almost all cases of acquired B antigen have been found in individuals. This report concerns a group A2 patient with acquired B antigen. The family was not available for genetic studies. Nevertheless two facts were in favour of A2 genotype: 10 after acetylation of the patient's red cells the A1 reactivity which usually reappears or is increased on acquired B cells, did not appear. 20 The study of the serum alpha-N acetyl galactosaminyl transferase showed an optimal activity at pH7, as it is usually found in A2. The respective roles of anti acquired B antibodies, group A specific structures and bacterial enzyme properties in the occurrence of acquired B antigen are discussed.