Mixed γG-γM Cold Agglutinin

Summary A mixed γG-γM cold agglutinin occurring in a patient with hemolytic anemia associated with infectious mononucleosis is described. Utilizing the technique of quantitative complement fixation, both γG and γM were detected in a 4 to 3 ratio in the eluate. Neither the γM nor γG chromatographically separated fractions of the eluate showed any cold agglutinin activity alone. When these two fraction were mixed, cold agglutinin activity was re-established. The addition of normal γG to the chromatographically separated γM cold agglutinin or the addition of normal γM to the γG cold agglutinin did not result in detectable cold agglutinin activity. The agglutinating activity of the patient’s serum against O Rh positive red blood cells sensitized with an incomplete γG-antibody (anti-CD serum Ripley) was 500 times greater at 4°C than at 37°C. Evidence is presented which suggests that the γG component of the cold agglutinin was directed against red cell antigenic determinants, and that the γM component represented antibody active at 4°C against the γG coating the red cells, i.e., “cold anti-antibody.”.