Cold-induced augmentation of I blood group antigen interactions with galactophilic lectins

The I antigen appears on human cells in the postnatal period, by addition of N-acetyllactosamine (β1-6) branching to the fetal i antigen structure, which is specified by linear oligo N-acetyllactosamine (β1-3) chain. Concurrently with the I antigen appearance on adult human erythrocytes most human sera exhibit low levels of anti-I agglutinins. These antibodies induce hemagglutination mainly at low temperatures (4°C) and scantly at body temperature. Therefore they were named 'cold agglutinins'. We have used these antibodies and several hemagglutinating galactophilic animal, plant, and microbial lectins that also react with the I antigen, to study whether the cold-favored agglutination of the I antigen-bearing cells is a peculiar property of the anti-I antibodies or a special trait of that antigen. It has been found that the interactions of all of the examined lectins, irrespective of their source, with the adult human erythrocytes significantly increased at 4°C, in contrast to those of the same cells with diverse I-insensitive antibodies and lectins, which were significantly higher at room temperature.