The Lud cold agglutinin: a further antibody recognizing N-acetylneuraminic acid-determined antigens not fully expressed at birth.

From a patient, a new type of human cold aggluntinin, Lud, which reacts with a determinant involving N-acetylneuraminic acid and which is not fully expressed at birth, is described. This antibody differs from a recently described cold agglutinin, Fl. The antigenic determinant recognized by antibody Lud is diminished after treatment of erythrocytes with proteases, whereas that recognized by Fl is not.