The serum of people with blood group O contains not only classical anti-A and anti-B, but also anti-A,B antibodies, i.e., those whose Fab region equally recognizes both the A and B blood group antigens. The common epitope of the A and B antigens, recognized by these antibodies, is located strictly on one side of the tetrasaccharide molecule, which was shown by studying their complex with anti-A,B antibodies using the Saturation Transfer Difference (STD NMR) spectroscopy.
Tsygankova et al. (Mon,) studied this question.