INTERACTIONS OF SURFACTANT PROTEIN-A WITH INFLUENZA-A VIRUSES - BINDING AND NEUTRALIZATION

The interaction of pulmonary surfactant protein A (SP-A) with influenz a A H1N1 and H3N2 viruses was investigated. SP-A is a sialated C type lectin with affinity for mannose residues. Flow cytometry showed that binding of fluorescein isothiocyanate (FITC)-labeled SP-A to H3N2 viru s-infected cells was specific and time- and concentration-dependent. O ligosaccharides did not affect the binding of FITC-SP-A to the infecte d cells. Preincubation of H1N1 and H3N2 with SP-A resulted in a dose-d ependent reduction of the infectivity of the viruses to cells. Removal of the carbohydrate moiety of SP-A by N-glycosidase F or cleavage of its sialic acid residues by neuraminidase prevented the interactions o f SP-A with the viruses. It is concluded that SP-A binds to influenza A viruses via its sialic acid residues and, thereby, neutralizes the v irus.