IL-6 AND SOLUBLE IL-6 RECEPTORS (SIL-6R AND SGP130) IN HUMAN PLEURAL EFFUSIONS - MASSIVE IL-6 PRODUCTION INDEPENDENTLY OF UNDERLYING DISEASES

IL-6, soluble IL-6 receptor (sIL-6R) and soluble gp 130 (sgp 130) leve ls were measured in sera and pleural effusions from 42 patients with m etastatic carcinoma, non-Hodgkin's lymphoma, tuberculosis, cardiac fai lure and miscellaneous diseases. Pleural IL-6 levels measured by ELISA were very high in all patient groups (mean 34.8 +/- 15.3 ng/ml) witho ut significant difference according to diseases. IL-6 was shown to be biologically active in a proliferative assay. Serum IL-6 levels were l ow (0.049 +/- 0.014 ng/ml) and did not correlate with pleural fluid le vels. Pleural IL-6 levels correlated with the number of polymorphonucl ear cells in pleural fluid (P < 0.03). Pleural slL-6R levels (76 +/- 8 ng/ml) were always lower than serum levels (196 +/- 12 ng/ml; P < 0.0 001) but correlated with them (P < 0.01). Pleural sIL-6R and albumin l evels correlated (P < 0.01), suggesting a transudation of sIL-6R from the serum. Pleural sgp130 levels (10.9 +/-1.0 ng/ml) were lower than s erum levels (24.6 +/- 2.8 ng/ml; P < 0.002). After gel filtration of p leural fluid, the bulk of IL-6 (> 90%) was recovered in a 15 000-30 00 0 fraction, corresponding to the expected mel. wt of free IL-6. These results suggest a production and a sequestration of IL-6 in the pleura l cavity in all studied conditions.