A lymphocyte immunogenetic system, Atri, associated with the ABO blood group and the ABH secretor system.

The antigen Atri can be detected on the lymphocytes of 5.19% of A, ABH secretor individuals. The Atri substance is present in the plasma of the same individuals and can be fixed on group O erythrocytes. It is also found in the saliva of 30 out of 32 A non-secretor individuals. Its existence in the saliva of A secretor individuals, however, cannot be proved due to the presence of both the A and Atri antigens. The A AND Atri antigens have been shown to be distinct on lymphocytes by capping and by blocking of the A sites. The fact that in several families the Atri antigen is not expressed by the parents shows that its expression on lymphocytes requires the intervention of at least one gene in addition to ABO and Se.