Autoantibodies of U Blood Group Specificity in Autoimmune Haemolytic Anaemia

Autoantibody specificity in acquired haemolytic anaemia of the warm antibody type has been thought to be directed against Rh antigens or the precursors from which they arise. In many cases Rh_null red cells fail to react with these antibodies, providing apparent support for the assumption that they have Rh specificity. Rh_null red cells are also non-reactive with anti-U sera, and in addition have abnormal S and s antigens. We have studied 50 cases of warm antibody autoimmune haemolytic anaemia looking particularly for possible U, S or s blood group specificity of the causative antibodies. In the majority of cases the antibodies were found to be directed against antigens of the Rh complex, but in three cases multi-specific autoantibodies were shown to have complex specificity involving the Rh and U blood groups.