A Human Monoclonal IgM k Cold Agglutinin Recognizing Oligosaccharides with Immunodominant Sialyl Groups Preferentially at the Blood Group M‐Specific Peptide Backbone of Glycophorins: Anti‐PrM

A kappa-monotypic IgM high titer cold agglutinin reacting like anti-Pr at low, like anti-M at higher temperatures, is described. It recognizes tetra- and/or trisaccharides with immunodominant sialyl groups on glycophorins A, B, C like anti-Pr. Its affinity to the oligosaccharides is, however, approximately 10-fold increased when they are attached to the M-specific peptide backbone of glycophorin A. The antibody, termed anti-PrM, occurred in a blood group MN patient with chronic cold agglutinin disease and caused autoimmune hemolytic anemia.