Interleukin 10 (IL-10) regulation of tumour necrosis factor α (TNF-α) from human alveolar macrophages and peripheral blood monocytes

Abstract

Background - Regulation of the inflammatory response within the human lung is essential to prevent this important part of the normal host defence response becoming a pathological process. Tumour necrosis factor α (TNF-α) is a cytokine involved in the pathogenesis of shock and in granuloma formation, tissue necrosis, and fibrosis in many organ systems including the lung. Interleukin 10 (IL-10) has been proposed as having an inhibitory effect on the production of several inflammatory cytokines including TNF-α. Methods - The effect of IL-10 administration on TNF-α production was explored in human alveolar macrophages and peripheral blood monocytes from matched individuals. The effects of IL-10 on TNF-α protein production were determined by sandwich enzyme linked immunosorbant assay (ELISA), whereas the TNF-α mRNA response was established by Northern blotting using a TNF-α specific oligonucleotide probe. The protein synthesis inhibitors actinomycin D and cyclohexamide were utilised to monitor IL-10 effects on mRNA degradation and de novo protein synthesis, respectively. Results - The lipopolysaccharide-mediated TNF-α production in alveolar macrophages was reduced from 3.508 (0.629) to 2.035 (0.385) ng/ml by 100 U/ml IL-10. Lipopolysaccharide-induced TNF-α production in peripheral blood monocytes was reduced from 2.035 (0.284) to 0.698 (0.167) ng/ml. TNF-α gene expression was also inhibited in both alveolar macrophages and peripheral blood monocytes; lipopolysaccharide-induced TNF-α mRNA was reduced by 47.8 (15.2)% and 83.1 (4.2)%, respectively, by IL-10. The IL-10 mediated suppression of TNF-α mRNA was unaffected by addition of cyclohexamide, suggesting that de novo protein synthesis was not required for TNF-α inhibition. mRNA stability experiments indicated no acceleration in lipopolysaccharide-induced TNF-α mRNA degradation in response to IL-10. Conclusions - These findings suggest that IL-10 is a potent inhibitor of TNF-α expression and release from alveolar macrophages and peripheral blood monocytes, and thus it may have an important role in the cytokine network of the pulmonary immune response.