[125I]IgM (KAU) human monoclonal cold agglutinin: labelling and studies on its biological activity.

In order to study the interaction between an IgM cold agglutinin and the erythrocyte I antigen, the former antibody was labelled with 125I using the Chloramine-T, IODOGEN and Bolton-Hunter methods. High incorporation and adequate stability of the labelled IgM were obtained with all procedures. However, suitable biological activity was maintained only with the Bolton-Hunter method. Further studies suggest that tyrosine iodination affects antigen recognition by this IgM, whereas iodination of amino groups does not. The reagent thus prepared allowed the determination of the number of I sites per erythrocyte as well as the antibody affinity constant.