Identification of a lectin activity in Pneumocystis carinii

Pneumocystitis carinii is known to adhere to pulmonary alveolar epithelial cells in vivo and to epithelial cell lines in vitro by a mechanism unknown at the molecular level. P. carinii is now found to adhere to rabbit and human red blood cells leading to rosette formation and hemagglutination. P. carinii erythrocyte-adherence was best inhibited by bovine submaxillary mucin and by a polysaccharide from the wall of group A Streptococcus, and to a lesser extent by Streptococcus group C polysaccharide, asialofetuin and fetuin. Among the mono- and oligosaccharides tested, only lactose inhibited hemagglutination. Other glycoconjugates and oligosaccharides tested were inactive. P. carinii also bound to purified glycoproteins coupled to Sepharose or adsorbed to plastic, and the binding was inhibited by soluble bovine submaxillary mucin. These results indicate that P. carinii has a novel surface lectin that may be important in adherence to lung alveolar epithelial cells.