Pleural fluid interferon-gamma and tumour necrosis factor-alpha in tuberculous and rheumatoid pleurisy

Tuberculous and rheumatoid pleural effusions show features suggesting a strong local cellular immune response. Pleural fluid (Pf) from patients with tuberculosis, rheumatoid arthritis (RA) and other diseases were compared with respect to interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). Immunoassays were used to determine Pf-IFN-gamma and Pf-TNF-alpha in 102 patients, including 11 with RA, 31 with verified tuberculosis, 23 with suspected tuberculosis, 11 with pneumonia, 14 with lung cancer and 12 with congestive heart failure. Measurable Pf-IFN-gamma occurred exclusively in patients with verified (median 1.8 ng x mL-1; 95% confidence interval (95% CI) 0.63-4.0 ng x mL-1) or suspected (0.37 ng x mL-1; 95%CI 0-0.7 ng x mL-1) tuberculosis. The highest median Pf-IFN-gamma was observed in those patients who showed a positive pleural fluid culture for Mycobacterium tuberculosis. In pleural effusions due to other diseases, including RA, IFN-gamma was undetectable. The highest Pf-TNF-alpha occurred in verified tuberculosis (median 198 ng x L-1; 95% CI 169-222 ng x L-1) and RA (210 ng x L-1; 95% CI 147-231 ng x L-1). Pleural fluid interferon-gamma is a highly useful marker for diagnosing tuberculous pleurisy. Although tuberculous and rheumatoid pleural effusions share several biochemical features, they are strikingly different with respect to interferon-gamma.