Compartmentalization of pro-inflammatory cytokines in tuberculous pleurisy

Increased levels of interleukin-6 (IL-6) and IL-8 are found in various immunologically mediated inflammatory disorders. Concentrations of IL-6, IL-8 and the soluble form of the IL-6 receptor (sIL-6R) were determined in serum and effusion fluid of 25 patients with tuberculous pleurisy utilizing enzyme linked immunosorbent assays (EIA). Serum IL-6 levels were only slightly increased in patients with tuberculous pleurisy in comparison to controls (11.1 +/- 2.1 vs 7.3 +/- 1.0 pg ml-1). IL-8 could not be detected in the serum of tuberculosis patients, but it was detected in the serum of healthy controls (8.0 +/- 1.5 pg ml-1). In comparison to serum, IL-6 and IL-8 were found in high concentrations in pleural effusions (IL-6: 932 +/- 70 vs 11.1 +/- 2.1 pg ml-1, P < 0.0001; IL-8: 450 +/- 85 vs 0 +/- 0 pg ml-1). In contrast, sIL-6R concentrations were much higher in serum compared to pleural effusion levels [30,477 +/- 1905 vs 9881 +/- 1177 pg ml-1, P < 0.0001 (mean +/- SEM)]. The authors conclude that elevated levels of IL-6 and IL-8 in pleural effusions are compartmentalized at the site of active disease. The low levels of sIL-6R in the presence of high levels of IL-6 in pleural effusions, and the high levels of sIL-6R in the presence of low levels of IL-6 in serum suggest that the expression or shedding of sIL-6R may be downregulated in the presence of excessive amounts of IL-6.