SPECIFIC BINDING OF SURFACTANT APOPROTEIN SP-A TO RAT ALVEOLAR MACROPHAGES

Surfactant protein A (SP-A) influences the function of alveolar macrophages in vitro. In this study the characteristics of the binding of I-125-labeled SP-A to rat alveolar macrophages has been investigated. The binding of SP-A to alveolar macrophages at 4-degrees-C was saturable with half-maximal binding at a SP-A concentration of 4-mu-g/ml. Bound SP-A was rapidly displaced by an excess of unlabeled SP-A. The binding of labeled SP-A to the alveolar macrophages was blocked in a dose-dependent fashion by unlabeled SP-A, the collagen-like protein C1q and type V collagen but not by bovine serum albumin. These results suggest that a component of the interaction between SP-A and alveolar macrophages is mediated through the collagen-like domain of SP-A and that the characteristics of this interaction are consistent with there being a specific receptor for SP-A on the surface of alveolar macrophages.