In Vitro Tumor Necrosis Factor- α Secretion by Monocytes from Patients with Cystic Fibrosis

Immunoreactive tumor necrosis factor-alpha (TNF-alpha) concentration is increased in plasma from patients with cystic fibrosis and chronic Pseudomonas aeruginosa pulmonary infection. To determine if circulating monocytes could be the source of plasma TNF-alpha, we determined in vitro basal and endotoxin-stimulated TNF-alpha secretion by monocytes. In 10 adult patients studied at the time of a symptomatic respiratory exacerbation, basal secretion of TNF-alpha was significantly less than that for 10 matched healthy controls (median 265 pg/micrograms DNA, nonparametric 95% confidence interval 193 to 463 pg/micrograms DNA versus 575, 298 to 923 pg/micrograms DNA; P less than 0.006), although both groups responded equally effectively to added Escherichia coli endotoxin at greater than or equal to 25 ng/ml. In six patients and six matched controls, monocyte culture was repeated after completion of 2 wk anti-pseudomonal antibiotic treatment in the patients. The reduced basal TNF-alpha secretion in the patients had reversed and was not significantly different to that of controls. This effect mirrored a significant reduction in plasma immunoreactive TNF-alpha in these patients (mean +/- SD, 258 +/- 59.3 pg/ml pretreatment versus 133 +/- 47.8 pg/ml post-treatment; P less than 0.05). These findings suggest that a reversible downregulation of TNF-alpha secretion occurred at the time of a symptomatic respiratory deterioration in the presence of chronic P. aeruginosa infection. This may represent a physiologic regulatory mechanism to maintain a local inflammatory response to chronic pulmonary infection in cystic fibrosis.