Tumour necrosis factor-α expression and cell recruitment in Sephadex particle-induced lung inflammation: effects of dexamethasone and cyclosporin A

Abstract

1. Tumour necrosis factor-α (TNF-α) is a cytokine with diverse properties consistent with a possible role in inflammatory disease. We investigated whether TNF-α is induced during the progression of lung inflammation elicited by a particulate non-antigenic stimulus, and whether pharmacological control of TNF-α expression influences recruitment of specific inflammatory cell types.

2. A single intravenous injection of Sephadex particles into rats led to extensive granulomatous inflammation in lung alveolar and bronchial tissue that peaked in intensity after 24–72 h. Mononuclear cells were the principal component of granulomas, but neutrophils and eosinophils were also abundant. Numbers of mononuclear cells, neutrophils and eosinophils recovered by bronchoalveolar lavage (BAL) peaked at 72 h, 48 h and 72 h, respectively.

3. Messenger RNA encoding TNF-α was induced in lung epithelial cells, lung granulomas and BAL cells 6 h after Sephadex administration and remained elevated for 72 h before declining to baseline by 7 days. In BAL cell populations TNF-α protein was localized to mononuclear cells at all times points pre- and post-Sephadex administration.

4. Treatment of rats with dexamethasone significantly reduced the Sephadex-induced recruitment of mononuclear cells, neutrophils and eosinophils into the bronchoalveolar cavity, and significantly reduced TNF-α mRNA expression by BAL cells.

5. Treatment of rats with cyclosporin A was without effect on Sephadex-induced elevations of mononuclear cell numbers and expression of TNF-α, but did reduce significantly recruitment of neutrophils and eosinophils to BAL cell populations.

6. These results show that a sequential asthma-like recruitment of neutrophils, eosinophils and mononuclear cells into lung tissue can be induced by single exposure to a non-antigenic stimulus. Pharmacological and histological studies reveal that mononuclear cell mobilization relates closely to induced TNF-α expression, whereas mobilization of neutrophils and eosinophils appears secondary to expression of the cytokine.

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