TNF and IL-6 mediate MIP-1α expression in bleomycin-induced lung injury

Abstract

Previously, macrophage inflammatory protein-1␣ (MIP-1␣), a member of the C-C chemokine family, has been implicated in bleomycininduced pulmonary fibrosis, a model of the human disease idiopathic pulmonary fibrosis. Neutralization of MIP-1␣ protein with anti-MIP-1␣ antibodies significantly attenuated both mononuclear phagocyte recruitment and pulmonary fibrosis in bleomycin-challenged CBA/J mice. However, the specific stimuli for MIP-1␣ expression in the bleomycininduced lesion have not been characterized. In this report, two mediators of the inflammatory response to bleomycin, tumor necrosis factor (TNF) and interleukin-6 (IL-6), were evaluated as putative stimuli for MIP-1␣ expression after bleomycin challenge in CBA/J mice. Elevated levels of bioactive TNF and IL-6 were detected in bronchoalveolar lavage (BAL) fluid and lung homogenates from bleomycin-treated CBA/J mice at time points postbleomycin challenge, which precede MIP-1␣ protein expression. Treatment of bleomycin-challenged mice with soluble TNF receptor (sTNFr) or anti-IL-6 antibodies significantly decreased MIP-1␣ protein expression in the lungs. Furthermore, normal alveolar macrophages secreted elevated levels of MIP-1␣ protein in response to treatment with TNF plus IL-6 or bleomycin plus IL-6, but not TNF, bleomycin, or IL-6 alone. Finally, leukocytes recovered from the BAL fluid of bleomycin-challenged mice secreted higher levels of MIP-1␣ protein, compared to controls, when treated with TNF alone. Based on the data presented here, we propose that TNF and IL-6 are part of a cytokine network that modulates MIP-1␣ protein expression in the profibrotic inflammatory lesion during the response to intratracheal bleomycin challenge.

Cytoplasmic deposition of NFκB decoy oligonucleotides is insufficient to inhibit bleomycin-induced pulmonary inflammation

“…26 Following bleomycin administration, a complex spatial and temporal network of inflammatory mediators is upregulated. 3,6,27,28 We chose to measure the effect of NF B decoy ODN on IL-6 production. IL-6 has been shown to be involved in bleomycin-induced inflammation 28,29 and is produced by a variety of cell types, including epithelial cells and macrophages.…”

“…3,6,27,28 We chose to measure the effect of NF B decoy ODN on IL-6 production. IL-6 has been shown to be involved in bleomycin-induced inflammation 28,29 and is produced by a variety of cell types, including epithelial cells and macrophages. 30,31 There is also good evidence that secretion of IL-6 is regulated through NF B 32 and NF B consensus binding sites have been identified in the promoter of the IL6 gene.…”

“…30,31 There is also good evidence that secretion of IL-6 is regulated through NF B 32 and NF B consensus binding sites have been identified in the promoter of the IL6 gene. 33,34 We also measured the effect of NF B decoy ODN on total and differential cell counts, as it is well documented that inflammatory cell chemokines, such as macrophage inflammatory protein-1␣ and macrophage inflammatory protein-2, which are involved in the generation of bleomycin-induced lung damage, 28,35 are regulated through NF B. 36 Topical administration of NF B decoy ODN did not attenuate IL-6 or total and differential cell counts in the bleomycin model.…”

“…For example, the proinflammatory cytokine IL-6 can be produced by alveolar and bronchial epithelial cells, 37,38 as well as alveolar macrophages. 39 Smith et al 28 have proposed a cytokine network where initially TNF-␣ and IL-6 are secreted from airway epithelial cells and resident alveolar macrophages, leading to recruitment and stimulation of additional inflammatory cells into the lesion area. These inflammatory cells are mainly responsible for the inflammation and fibrotic lesions in the bleomycin treated lung.…”

TNF-α–stimulated fibroblasts secrete lumican to promote fibrocyte differentiation

“…We used TNF-α as the stimulus, as other profibrotic cytokines such as IL-4, IL-13, and TGF-β act directly on monocytes to regulate fibrocyte differentiation (31). TNF-α is produced by monocytes, macrophages, and fibrocytes, serum TNF-α levels are increased in fibrosis patients, and TNF-α induces fibrosis in animal models (32)(33)(34)(35)(36).…”