Specificity of IgA cold agglutinins: anti-Pr 1 .

Abstract

AbstractMonoclonal cold agglutinins have usually been found to be IgM(k) and to be directed against the I/i antigens.Three IgA(k) cold agglutinins were tested for antibody specificity. Based on the following criteria, they were shown to be directed against the Pr1 antigen of the Pr1/Pr2/Pra antigen system. The antigens reacting with the IgA(k) cold agglutinins were inactivated by protease and treatment of human red cells with neuraminidase and were demonstrable on human erythrocyte glycoproteins. The terminal sugar of the determinant group of these antigens is N‐acetylneuraminic acid (NANA), which is not involved in I/i, but also in Pr2 antigenicity. The antigen activity of these antigens and the Pr2 and I antigen activities were distributed to different glycopeptide fractions obtained from red cell glycoproteins by ficin cleavage and Sephadex G‐50 separation. Periodate oxidation of red cell glycoproteins, which causes a shortening of the polyhydroxy side chain at C‐6 of C‐9 NANA to a C‐7 and/or C‐8 NANA derivative, resulted in inactivation of these antigens, while the I antigen remained unchanged and the Pr2 antigen was increased 16–64‐fold. Dog red cells gave no or diminished reactions with the three IgA(k) cold agglutinins, in contrast to increased reaction with anti‐Pr2. Based on the different reactions of the IgA(k) cold agglutinins with dog red cells, a Pr1 heterogeneity Pr1h/Pr1d was demonstrated.In spite of the determination of the Pr1h/Pr1d/Pr2 and the MN antigens by NANA, both antigen systems were shown to be unrelated. Blocking of free ε‐lysine amino groups by acetylation or blocking of the NANA carboxyl groups by amidation of red cell glycoproteins resulted in MN inactivation, while the antigens reacting with the IgA(k) cold agglutinins (like Pr2) remained unaffected.The anti‐Pr1 specificity of IgA cold agglutinins and the predominance of anti‐I/‐i specificity of IgM cold agglutinins was discussed with respect to inter‐relations between immunoglobulin classes and antibody specificities of cold agglutinins.