Influence of Surfactant on Cytokine Release from Ozone-Exposed Human and Bovine Alveolar Macrophages in Vitro

Abstract

Previous studies at our laboratory demonstrated that ozone, a ubiquitous air pollutant, was able to induce the liberation of cytokines from alveolar macrophages (AM) in vitro. As the lung cells in the alveoli are lined by surfactant, we exposed to ozone in this study surfactant-coated human (HAM) and bovine (BAM) alveolar macrophages in order to examine isolated cells under conditions that simulate as nearly as possible the in vivo situation in the lung. BAM were incubated with 0.25, 0.5, or 1 ppm ozone for 2 or 4 h in the presence or absence of the synthetic surfactant surrogate Alveofact or dipalmitoyl lecithine (DPL), the major lipid of natural surfactant. Incubations of BAM with Alveofact led, for 1 ppm ozone, to a significant suppression of the ozone-induced liberation of tumor necrosis factor α (TNF-α) and Mac-ChF, a chemotactic factor for macrophages, and DPL also reduced significantly the ozone-elicited Mac-ChF release when 0.5 ppm ozone was tested. When we exposed BAM to a combination of 1 ppm ozone and lipopolysaccharide (LPS), the Mac-ChF release was not more than additive, but DPL coating of the cells reduced, in spite of ozone treatment, the Mac-ChF liberation down to the level that had been observed with LPS alone. HAM were obtained from a patient with chronic obstructive bronchitis and showed a high spontaneous TNF-α secretion, an observation that in one case was also made for BAM. However, pretreatment of the cell cultures with Alveofact (BAM) or DPL (HAM) reduced these basal secretions of TNF-α (BAM and HAM) and Mac-ChF (BAM) significantly. As had already been demonstrated for BAM, DPL was also capable of inhibiting ozone-induced TNF-α release from HAM. Taken together, the data of this in vitro study showed that the surfactant substitutes Alveofact and DPL are able to reduce the concentration of TNF-α and of the chemoattractant Mac-ChF in the culture medium. Additionally, high spontaneous cytokine levels from both HAM and BAM were reduced by surfactant coating of the cells. It cannot yet be decided whether these effects are due to mere “mechanical'' protection, downregulation of secretion, or interaction of released cytokines with surfactant.