This report presents experimental observations indicating the presence of an inhibitory activity in cystic fibrosis (CF) serum which impairs phagocytosis of Pseudomonas aeruginosa by rabbit as well as human alveolar macrophages. Of the 49 patient serum samples studied, 40 consistently showed ≥ 60% inhibition, 3 showed no inhibition and 6 were in the range of 20–60% inhibition of Pseudomonas phagocytosis. In parallel studies, the phagocytosis of S. aureus and S. marcescens was found not to be inhibited by CF serum. Mixing of CF serum with normal serum could not overcome the inhibitory effect, indicating the presence of an inhibitory factor rather than the lack of a necessary component. The inhibitory activity is not lost upon exposure of serum to glass, upon freezing the serum once, or upon heating at 56 C for 30 minutes.
The serum of cystic fibrosis patients selectively inhibits alveolar macrophage function in vitro; the expression of this inhibitory activity in vivo may compromise effective host control of infection. Investigation of the origin, nature and pathophysiologic role of the activity may suggest new approaches to the control of Pseudomonas pulmonary infection.