A new approach to the thermodynamic study of ABO antibodies.

Enthalpy change was determined for natural anti-A (B, O subjects) and anti-B (A1, A2, O subjects). Entropy change, free energy change and association constant were calculated according to the law of mass action and the Wurmser method. The concentrations of allohaemagglutinins were measured by the Wilkie and Becker method using an autoanalyser. 2-Mercaptoethanol was used to estimate the proportions of IgG and IgM and their respective contribution to the thermodynamic properties. The following results and conclusions were obtained. Individual enthalpy and entrophy changes are different for each subject so that only the average values of these thermodynamic parameters represent a characteristic of the phenotype. There is a correlation between enthalpy and entropy changes and the relative proportion of anti-A or anti-B IgG. There is heterogeneity of the values of association constant. Free energy change is about 10 kcal mol-1 for all anti-A and anti-B; this result confirms the low energy binding between antigen and antibody. All these results confirm the role of environment and red-cell phenotype in the synthesis of allohaemagglutinins.