In Vitro Acute Effects of Tobacco Smoke on Tumor Necrosis Factor a and Interleukin-6 Production by Alveolar Macrophages

Abstract

Tobacco smoke is a usual form of oxidant aggression present in the domestic environment. In the present study, the in vitro acute effects of a 2-cigarette smoke gas phase were evaluated on cell viability and cytokine secretion by alveolar macrophages (AM) from guinea pigs and human healthy subjects. Cell injury was estimated immediately after smoke exposure by evaluation of ATP cell content (measured by bioluminescence) and lactic dehydrogenase (LDH) release in the culture medium. LDH release was also measured when the interleukin-6 (IL-6) and tumor necrosis factor a (TNF) activities were evaluated. No cytotoxic effect was found: The ATP cell content of both guinea pig AM and human AM did not significantly change after tobacco smoke exposure. Similarly, the LDH release in the culture medium was unchanged both immediately after tobacco smoke exposure and at the time of the cytokine evaluation (18-20 h later) compared to cells cultured in the air. The total protein synthesis by the guinea pig AM evaluated by ³⁵S-L-methionine labeling was unaffected by tobacco smoke exposure. The production of IL-6 and TNF activities was evaluated 18-20 h after smoke exposure. The IL-6 activity was measured by the proliferation test of 7TD1 hybridoma cell line; the TNF activity was evaluated by the L929 mouse fibroblast cytotoxic test and by an immunoradiometric assay (for human AM). A 2-cigarette smoke exposure decreased both activities significantly. The exposure of the guinea pig AM reduced IL-6 activity by 24.3 ± 6.7%, 42.4 ± 7.8%, and 39.7 ± 9.6% and TNF activity by 33.8 ± 10.4%, 35.1 ± 10.7%, and 38.8 ± 9.9% (respectively unstimulated cells and AM activated by 0.1 and 10 μg LPS/mL). The decrease in monokine production by the human AM was, respectively, 57.8 ± 8.8%, 59.7 ± 11.4%, and 49.9 ± 10.5% of IL-6 activity and 37.4 ± 14.6%, 17.6 ± 9.6%, and 37.2 ± 6.3% of TNF activity. The possible release of cytokine inhibitors was also investigated. The inhibitory activity against recombinant TNF and IL-6 was evaluated in culture medium from unstimulated AM exposed to tobacco smoke and did not significantly differ from that of AM exposed to air, demonstrating that the decrease of monokine levels could not be explained by the release of inhibitory factors. In contrast, the alteration of monokine release by AM exposed to tobacco smoke seemed to be mainly due to a defect of the cytokine production, since the TNF and IL-6 intracellular expressed as the percentage of total monokine activity produced by these cells were not significantly different between AM exposed to air or to cigarette smoke whatever the situation studied. Since TNF and IL-6 are important factors in normal host defenses, impaired response due to cigarette smoke might explain, at least in part, the increased susceptibility of smoking patient to infections.