Effects of tobacco smoke on IL-16 in CD8+ cells from human airways and blood: a key role for oxygen free radicals?

Abstract

Chronic exposure to tobacco smoke leads to an increase in the frequency of infections and in the number of CD8+ and CD4+ cells as well as the CD4+ chemoattractant cytokine IL-16 in the airways. Here, we investigated whether tobacco smoke depletes intracellular IL-16 protein and inhibits de novo production of IL-16 in CD8+ cells from human airways and blood while increasing extracellular IL-16 and whether oxygen free radicals (OFR) are involved. Intracellular IL-16 protein in CD8+ cells and mRNA in all cells was decreased in bronchoalveolar lavage (BAL) samples from chronic smokers. This was also the case in human blood CD8+ cells exposed to water-soluble tobacco smoke components in vitro, in which oxidized proteins were markedly increased. Extracellular IL-16 protein was increased in cell-free BAL fluid from chronic smokers and in human blood CD8+ cells exposed to water-soluble tobacco smoke components in vitro. This was not observed in occasional smokers after short-term exposure to tobacco smoke. A marker of activation (CD69) was slightly increased, whereas other markers of key cellular functions (membrane integrity, apoptosis, and proliferation) in human blood CD8+ cells in vitro were negatively affected by water-soluble tobacco smoke components. An OFR scavenger prevented these effects, whereas a protein synthesis inhibitor, a β-adrenoceptor, a glucocorticoid receptor agonist, a phosphodiesterase, a calcineurin phosphatase, and a caspase-3 inhibitor did not. In conclusion, tobacco smoke depletes preformed intracellular IL-16 protein, inhibits its de novo synthesis, and distorts key cellular functions in human CD8+ cells. OFR may play a key role in this context.