Inhibitory effect of cystic fibrosis serum on pseudomonas phagocytosis by rabbit and human alveolar macrophages.

Summary: 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. Speculation: 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. Pultionary infection is a major factor in the morbidity and mortality associated with cystic fibrosis (CF) (6). Pseudomonas, a uhrquitous organism in the environment, is cystic fibrosis (CF) (6). Pseudomonas, a uhrquitous organism in the environment, is usually not pathogenic for healthy individuals. However, individuals with the chronic lung disease of CF are particularly susceptible to opportunistic Pseudomonas aeruginosa infections. The frequency of this organism in CF pulmonary infections is inadequately explained. It is well known that most CF patients have elevated levels of Pseudomonas antibodies in their sera and pulmonary secretions (l2,14). While recently there has been an indication that a lymphocyte unresponsiveness to Pseudomonas may be acquired as the infection progresses (18,19), no other immunologic abnormality has been consistendy observed (5.10). Extrapulmonary infection is extremely rare and sepsis is almost never, seen after the first months of life (22). This unusual susceptibility to Pseudomonas despite apparently normal systemic humoral and cellular immunity. suggests that local pulmonary host defense mechanisms are defective in CF. Several recent studies have indicated that lung defenses can, to a certain extent, function independently of systemic humoral and cell mediated immune systems (9,15,20,21). Lung defenses include mucociliary transport as well as phagocytic cells, lymphocytes, and immunoglobulin secretion. Since mucociliary transport in some CF patients is compromised (5). clearing of the bacteria becomes more dependent on the efficient action of the phagocytic cells. Previous studies in our laboratory (2) and by Biggar, et al. (I) have shown that CF serum impairs phagocytosis of Pseudomonas by rabbit alveolar macrophages. This report presents experimental observations indicating the presence of an inhibitory activity in CF serum which impairs phagocytosis of Pseudomonas by human as well as rabbit alveolar macrophages.