Red Cell Mucoproteins

Agglutination of red cells by influenza virus, and the concept of "receptor" areas on the cell surface which are enzymatically modified after contact with virus, were described by Hirst in 1942.17 Since that time much indirect evidence has been collected suggesting that virus receptors consist, at least in part, of mucoid substances; examples of this evidence are the inactiva-tion of receptors by periodate1' and the active competition with receptors by mucoids such as the "Francis inhibitor" of serum and ovarian cyst fluids,'" ovomucin,14"' and highly purified sheep salivary mucoid.' Direct isolation of specific receptor-substance mucoids from the complex lipoprotein of the erythrocyte surface is obviously more difficult than the purification of receptor analogues from soluble mucoid secretions. Virus-inhibitory extracts have, however, been prepared from red cells of various species by boiling stroma in water"5 or by extracting red cells in a Waring blendor.' A purified preparation isolated from human red cell stroma in the first instance as an ether-soluble lipomucoid was described in 1948 by deBurgh, Yu, Howe, and Bovarnick.' Their most active fraction contained at least 50%o reducing substances but was said to contain neither hexosa-mine nor phosphorus. In the same year Woolley'1 obtained a heat-labile polysaccharide substance from the supernatant fluid of hemolyzed erythro-cytes which was shown to antagonize the antihemagglutinin effect of apple pectin. After exposure to influenza virus the purified erythrocyte substance was no longer capable of inhibiting pectin, and it was concluded that the former material, which itself showed detectable inhibition of PR8 virus at 0.04 ,ug/ml.," was the substrate for enzymic attack by virus on the red cell surface. In an extensive study by Howe,1' which appeared while the present work was in progress, physical methods were described for the isolation