Clara cell secretory protein increases phagocytic and decreases oxidative activity of neutrophils

Horses suffer from recurrent airway obstruction, an asthma-like condition induced by repeat inhalation of environmental substances present in barn air. Clara cell secretory protein (CCSP) is much reduced during active inflammation when neutrophils predominate in the airways, and in chronic asthmatics. We sought to investigate morphologic and functional interactions of CCSP with neutrophils. Bronchoalveolar and blood neutrophils from healthy control animals, and from animals with recurrent airway obstruction in remission and exacerbation, were evaluated by immuno-cytochemistry and immuno-electron microscopy for presence of CCSP. Blood neutrophil oxidative burst and phagocytic activities were determined in the presence of different concentrations of recombinant equine CCSP. Bronchoalveolar lavage neutrophils from horses with exacerbated lung inflammation, but not from control horses, and not blood neutrophils from either group of animal, contained abundant immunoreactive CCSP. On immuno-electron microscopy, CCSP localized to the cytoplasm and nucleus. Incubation of blood neutrophils with CCSP significantly reduced oxidative burst activity (P < 0.0001) and increased phagocytosis (P < 0.001) of neutrophils. These findings indicate that CCSP enters neutrophils in horses with active neutrophilic lung inflammation and alters the function of neutrophils in blood. Presence in the nucleus suggests a potential transcriptional role of CCSP in neutrophils.