IL-5 in post-traumatic eosinophilic pleural effusion.

Thoracic trauma or pneumothorax can result in pleural fluid eosinophilia. In this study we investigated the role of the eosinophilopoietic cytokine IL-5 in three cases of post-traumatic eosinophilic pleural effusions (EPE). Using a specific immunoenzymatic assay, significant levels of IL-5 were found in EPE (range 100-3000 pg/ml), while IL-5 was undetectable (< 25 pg/ml) in corresponding serum samples and in non-eosinophilic pleural fluids. IL-5 present in pleural fluids was found bioactive in a proliferative assay using a mouse CTLL-2 cell line transfected with the cDNA corresponding to the alpha chain of the human IL-5 receptor. Using a reverse polymerase chain reaction (PCR) method, we found IL-5 mRNA expression within pleural mononuclear cells from patients with EPE, but not in corresponding peripheral blood mononuclear cells (PBMC), confirming that IL-5 is synthesized locally in the pleural cavity. In the two cases in which pleural CD4+ cells were purified, these cells were identified as the major source of IL-5. Taken together, these data indicate that the development of post-traumatic EPE is related to a local secretion of IL-5 by CD4+ cells present in the pleural cavity.