Lung and salivary scavenger receptor glycoprotein-340 contribute to the host defense against influenza A viruses

The lung scavenger receptor-rich protein glycoprotein-340 (gp-340) is present in bronchoalveolar lavage (BAL) fluids and saliva and mediates specific adhesion to and aggregation of bacteria. It also binds to surfactant proteins A and D ( SP-A and - D). Prior studies demonstrated that SP-A and SP-D contribute to innate defense against influenza A virus (IAV). We now show that lung and salivary gp-340 inhibit the hemagglutination activity and infectivity of IAV and agglutinate the virions through a mechanism distinct from that of SP-D. As in the case of SP-A, the antiviral effects of gp-340 are mediated by noncalcium-dependent interactions between the virus and sialic acid-bearing carbohydrates on gp-340. Gp-340 inhibits IAV strains that are resistant to SP-D. Concentrations of gp-340 present in saliva and BAL fluid of healthy donors are sufficient to bind to IAV and inhibit viral infectivity. On the basis of competition experiments using competing saccharide ligands, it appears that SP-D does not entirely mediate that anti-IAV activity of BAL fluid and contributes little to that of saliva. Furthermore, removal of gp-340 from BAL fluid and saliva significantly reduced anti-IAV activity. Hence, gp-340 contributes to defense against IAV and may be particularly relevant to defense against SP-D-resistant viral strains.