The natural heterohaemagglutinin in the serum of the toad Bufo regularis, and its relationship to lower vertebrate immunoglobulins.

The serum of the toad Bufo regularis contains a natural heterohaemagglutinin for human erythrocytes, Which appears to have anti-(B + HP) specificity. Results of inhibition and absorption experiments indicate that only one agglutinin is present. The biochemical specificity of the agglutinin may be provisionally described as involving alpha-D-galactose residues linked (1-3) in the B determinant, of red cells possessing the H ANTIGEN. Unlike amphibian IgM, the agglutinin was insensitive to 2-mercaptoethanol treatment; moreover, it could be eluted from the alpha1 globulin region on cellulose acetate electrophoresis. These results suggest that this naturally occurring heterohaemagglutinin has a structure similar to that of plant and animal lectins. The relationship of this observation to the phylogenetic evolution of immunity is discussed.