BINDING OF PULMONARY SURFACTANT PROTEIN-A AND PROTEIN-D TO ASPERGILLUS-FUMIGATUS CONIDIA ENHANCES PHAGOCYTOSIS AND KILLING BY HUMAN NEUTROPHILS AND ALVEOLAR MACROPHAGES

To determine whether the lung surfactant proteins A (SP-A) and D (SP-D ) are involved in the initial protective immunity against opportunisti c pulmonary fungal infections caused by Aspergillus fumigatus, we perf ormed a series of in vitro functional studies to see if SP-A and SP-D enhanced binding, phagocytosis, activation, and killing of A. fumigatu s conidia by human alveolar macrophages and circulating neutrophils. B oth SP-A and SP-D bound to carbohydrate structures on A. fumigatus con idia in a calcium-dependent manner. SP-A and SP-D were also chemoattra ctant and significantly enhanced agglutination and binding of conidia to alveolar macrophages and neutrophils, Furthermore, in the presence of SP-A and SP-D, the phagocytosis, oxidative hurst, and killing of A. fumigatus conidia by neutrophils were significantly increased. These findings indicate that SP-A and SP-D may have an important immunologic al role in the early antifungal defense responses in the lung, through inhibiting infectivity of conidia by agglutination and by enhancing u ptake and killing of A. fumigatus by phagocytic cells.