Surfactant protein A binding to cytomegalovirus proteins enhances virus entry into rat lung cells

The role of surfactant protein (SP)-A in cytomegalovirus (CMV) infection of the lung was investigated. We found that SP-A binds to various immobilized human CMV proteins and those exposed on the surface of infected embryonal lung fibroblasts. The interaction between SP-A and immobilized CMV proteins was found to be calcium-dependent and inhibited by mannan, suggesting involvement of the carbohydrate recognition domain of SP-A and high-mannose carbohydrate residues of viral envelope glycoproteins. Using flow cytometry and confocal laser fluorescence microscopy in the rat model we showed that preincubation of rat CMV with SP-A stimulates its binding and internalization by rat type II pneumocytes and alveolar tissue macrophages. This effect was concentration- and Ca(2+)-dependent but was not inhibited by mannan. Therefore, the domains of SP-A involved in SP-A CMV interaction and in interaction of the SP-A/virus complex with rat lung cells are distinct. Additionally, in the human CMV model, sheep as well as human proteinosis SP-A did not significantly affect human CMV replication in embryonal lung fibroblasts. Thus, SP-A may contribute to CMV-associated pathology of the lung by increasing the efficiency of target cell infection.