Elevated pleural fluid levels of defensins in patients with empyema

Defensins, also known as human neutrophil peptides, are antimicrobial peptides present in the azurophil granules of neutrophils. We measured their level in pleural effusion in various pulmonary diseases to investigate whether they could be used as a diagnostic marker in the differential diagnosis of specific pleural diseases.

We analyzed pleural effusion samples collected from 61 patients, including 50 exudates (11 with empyema, 3 parapneumonic, 15 tuberculous, 18 neoplastic, 3 miscellaneous) and 11 transudates as controls.

Defensins were measured by radioimmunoassay and also analyzed by reverse-phase high-performance liquid chromatography. The concentrations of interleukin (IL)-8 and granulocyte colony-stimulating factor (G-CSF) in pleural effusion fluid were measured by enzyme-linked immunosorbent assay to examine the correlation between these cytokines and defensins.

The concentration of defensins in all samples of empyema was >5,100 ng/mL and the mean concentration (13,265.8+/-1,895.2 ng/mL) in these samples was the highest among other groups. The concentration in the other 50 pleural effusion samples tested was <2,800 ng/mL. Defensins were mostly of the mature type in empyema. Pleural effusion levels of IL-8 and G-CSF in patients with empyema were also significantly higher than those in other samples. There was a significant correlation between defensins and IL-8 or G-CSF in pleural effusion fluid (r=0.762, and 0.827, respectively).

Our results suggest that the high effusion concentrations of defensins in pleural effusion may constitute an important component of the host defense system or may have a cytotoxic role in empyema. Our results also indicate that the high levels of IL-8 and G-CSF in empyema may indirectly explain the elevated levels of defensins by increasing the number of neutrophils in the pleural space.