Hemolytic Anemia with Cold Detectable IgG Antibodies

Erythrocytes obtained from patients who manifest autoimmune hemolytic anemia can be divided into at least three categories by the nature of their protein coats as determined by direct antiglobulin (Coombs) test: IgG alone, IgG and complement (C), C alone. IgG antibodies were detected by direct Coombs Test at 4°C but not at 37°C in patients of type 3 A.H.A. Experiments at 4, 10, 15, 20, 30 and 37°C demonstrated that the IgG antibody was not eluted from the red cells at 37°C but apparently underwent a configurational change above 10°C such that agglutination no longer occurred with the Coombs reagent. This change was reversible. The presence of cold detectable IgG antibodies provides a mechanism for C deposition on erythrocytes in some cases of A.H.A., ostensibly due to complement alone.