Acetylated galactosamine is a receptor for the influenza C virus glycoprotein

We have investigated the specificity of influenza C virus receptor destroying enzyme (RDE) by treatment of erythrocytes of various species with influenza C virus followed by examination of the agglutination patterns of the erythrocytes with a panel of 13 lectins and four anti-human blood group sera of known receptor specificity. Human and animal erythrocytes were agglutinated by lectins SBA, DBA, WFA, VAA II, RCA II, and WGA which have a specificity for the N-acetyl group of galactosamine (NAc-D-Gal) or glucosamine (NAc-D-Gal); this effect was abolished after treatment of erythrocytes with influenza C virus. On the other hand, lectins (RCA I, PNA, APA) with a specificity for D-Gal were able to agglutinate erythrocytes both before and after influenza C virus treatment. Thus, influenza C virus RDE is able to cleave an acetyl group at the 'N' position of galactosamine or glucosamine in addition to acetyl groups in the 'O' position of neuraminic acid and acetylated amino sugars such as galactosamine may act as receptors for the haemagglutinin of influenza C viruses in addition to acetylated neuraminic acid.