Changes in 'A' antigenic sites in haematological disorders. An immunoautoradiographic study

Using a quantitative immunoautoradiographic technique with simultaneously exposed internal standards, antigenic sites on A1, A1B, A2 and A2B erythrocytes were quantitated. The binding of purified radioiodinated rabbit anti-A antibodies was studied by the direct incubation technique. 61 normal individuals and 44 patients suffering from leukaemia and other haematological disorders such as polycythaemia vera (PV) and aplastic anaemia (Apl.A) were investigated. Among the normal volunteers, antigenic sites gradually increased up to 3 months of life, later on they were comparable with the values of adults. A reduction of more than 50% in the antigenic sites was observed in all cases of Apl.A. 50-70% of patients with various forms of leukaemia had a decrease in antigenicity. 1 patient suffering from acute unclassified leukaemia showed two populations of red cells. This case differed from natural O/A1 chimerism where A1 erythrocytes had normal antigenicity while in the patient, A1 antigens were depressed. 2 patients (1 with acute lymphoblastic leukaemia, 1 with Apl.A) who were investigated after allogenic bone marrow transplantation had a marked decrease in antigenic sites. Reasons for A antigenic variations in haematological disorders are discussed.