Nature of human serum blood group T antibodies.

Antibodies against blood group substance T in normal human sera consist of two types, depending upon whether or not the molecules remain immunochemically active at 37 degrees C. The two agglutinins were isolated by means of T antigen-coupled Sepharose 48 affinity chromatography. Temperature-sensitive agglutinin was eluted from the affinity column at 37 degrees C, while temperature-independent agglutinin remained bound to the antigen. Subsequently, the latter was dissociated from the column in the presence of 2.5 M MgCl2. Examination of six normal sera revealed that the levels of temperature-independent agglutinin was about twice that of temperature-sensitive agglutinin. More than 90% of anti-T agglutinins in normal sera were of the IgM class, in 8 of 11 samples studied. No direct relationship appeared to exist between anti-T titers and blood type. Thermal effects on hemagglutination, at least for anti-T agglutinin interacting with T antigen bearing red cells, is primarily due to the molecular characteristics of the agglutinin and not to the conformational change of the red cell membranes.