Origin of heterogeneity of interleukin-6 (IL-6) levels in malignant pleural effusions.

We measured interleukin-6 (IL-6) concentrations from 48 malignant pleural effusions by an enzyme immunoassay and found a marked heterogeneity of the concentrations. The histological type of the malignant cells and total counts or differentials of the cells in effusions could not account for the heterogeneity. We newly established five malignant cell lines and found that the amounts of IL-6 produced by them were well correlated with IL-6 concentrations of the effusions from which these lines were derived (r=0.96; p<0.01). These results suggest that a marked heterogeneity of IL-6 concentrations in malignant effusions reflects the differential production of IL-6 by malignant cells in pleural space.