Chronic Hemolytic Anemia due to Cold Agglutinins: the Mechanism of Resistance of Red Cells to C′ Hemolysis by Cold Agglutinins*

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Abstract
The red cells of patients with chronic hemolytic anemia due to cold agglutinins are agglutinated by antiglobulin serum in a nongamma reaction due to the coating of β-globulins, C′4 and C′3. The red cells of such patients are abnormally resistant to C′ hemolysis by cold agglutinin. Normal red cells can be made equally resistant to C′ hemolysis by incubation with cold agglutinin and normal serum at temperatures which allow transient reactions between the red cells and cold agglutinins. The development of resistance to C′ hemolysis was related to increasing susceptibility to agglutination in anti-β1c- and anti-β1e-sera and by increasing uptake of 131I activity from labeled anti-β-globulin serum containing antibodies for both globulins. There was decrease in the adsorption of 131I-labeled cold agglutinin during the development of resistance to C′ hemolysis and reduced susceptibility to agglutination by cold agglutinins. Since cold agglutinins have been demonstrated to dissociate from the red cell, leaving fractions of C′ globulin attached, it is postulated that repeated transient reactions produce the accumulation of incomplete C′ complexes. Steric hindrance by the adsorbed C′ complexes is probably responsible for the inhibition of the reaction with cold agglutinin. There is evidence that the adsorbed C′ complexes also interfere with the hemolytic action of C′ even when cold agglutinin has become reattached to the red cells. The accumulation of C′ complexes by cold agglutinins appears to be the most important factor in the abnormal resistance to C′ hemolysis exhibited by the patient's red cells. Other factors, such as the heterogeneity within a population of normal cells, appear to be of minor significance.