Surfactant protein A stimulates release of neutrophil chemotactic factors by alveolar type II pneumocytes.

Mucosal immunity is an important mechanism in the response to injury. Our hypothesis is that surfactant protein A (SP-A) is an autocrine factor that stimulates alveolar type II epithelial cell release of neutrophil chemotactic factors by binding to the SP-A receptor expressed by these cells. We examined (1) the effect of SP-A (20 μg/ml) or IL-1β (10 ng/ml) on release of neutrophil chemotactic factors by primary cultures of type II cells or alveolar macrophages, and (2) the effect of intratracheal instillation of the blocking antibody to the SP-A receptor on the response to oleic acid-induced lung injury in vivo. All media and cell culture supernates were assayed for neutrophil chemotactic activity, and bronchoalveolar lavage fluid from the in vivo experiments was analyzed for inflammatory cell counts. While SP-A and media used for the cell cultures has no intrinsic neutrophil chemotactic activity, supernates from primary cultures of type II cells incubated in either SP-A or IL-1β had twofold higher neutrophil chemotactic factor activity compared to supernates from controls. SP-A had no effect on release of neutrophil chemotactic factor by alveolar macrophages. Oleic acid-induced lung injury resulted in a marked influx of neutrophils into BAL, and this influx was reduced by 70% by pretreatment with the antibody to SP-A receptor. We conclude that SP-A stimulates the release of neutrophil chemotactic factor by alveolar type II cells, and this effect is mediated by the receptor for SP-A specifically expressed by these cells.