[Cold agglutinin with anti-B specificity in an A1B subject].

A high titre cold autoagglutinin with anti-B specificity was found in the serum of an A1B group individual. It was associated with a low titre anti-I. This anti-B agglutinated most cells having a B antigen (normal B, A1B, A2B, from adult and cord bloods, B3), but failed to agglutinate Bx Cis-AB and Bh cells. Nevertheless, all these cells absorbed the anti-B SER at low temperatures. Fixation elution tests were also positive on the patient's cells and three consecutive absorptions on these cells completely removed the anti-B activity. The Coombs test was positive with anti-complement anti-globulin when the cells were sensitized by the serum at 4 degrees C. It was negative when the cells were sensitized at 37 degrees C. The patient did not show any sign of haemolysis. The anti-B was a IgM Kappa. Its reaction with normal B cells had an enthalpy change of - 36-000 cal./mole, i.e. very different from O ANd A individuals, but similar to that of the erythrocytic I antigen - anti-i antibody reaction. Quantitative measurements showed the erythrocyte B antigen similar to that of control A1B cells.