Effect of sequential glycolysis of the lectin of Euonymus europaeus on activation of the classical complement pathway in normal human serum.

The lectin of Euonymus europaeus at concentrations of 5-21 micrograms/ml causes activation of the classical complement (C) pathway (C1, C4, C2) when added to normal human serum at 37 degrees C. At higher concentrations, C3 is also consumed. The effect is dependent on a 'natural antibody' in serum of the IgM class which reacts with an epitope of the lectin. With physicochemical methods, the carbohydrate of the lectin was shown to be involved in the activation of C, but not involved in the agglutination of group B erythrocytes. Removal of N-acetyl-D-glucosamine from the lectin with an exoglycosidase greatly reduced the activation of C in serum, but it did not affect erythroagglutination. Using competitive binding studies with various sugars, it was confirmed that N-acetyl-D-glucosamine is the dominant specificity of a determinant for activation of the classical C pathway in serum.