Pulmonary epithelial cells facilitate TNF-alpha-induced neutrophil chemotaxis. A role for cytokine networking.

TNF-alpha and neutrophils are postulated to play important roles in several inflammatory lung diseases. Thus, we examined TNF-alpha-induced neutrophil migration through polycarbonate filters and human pulmonary type II-like epithelial (A549) cells cultured as monolayers on these filters. TNF-alpha induced both dose- and time-dependent migration of neutrophils across both barriers, but migration across A549 cells was much greater than that across naked filters. Migration of neutrophils across both barriers was completely inhibited by anti-TNF-alpha. Furthermore, supernatants of TNF-alpha (10(-9) M)-stimulated A549 monolayers induced threefold greater migration of neutrophils across naked filters than 10(-9) M TNF-alpha itself, suggesting release of soluble chemotactic factor(s). Pretreatment of A549 monolayers with actinomycin D inhibited both the production of soluble chemotactic factors and TNF-alpha-induced transcellular migration. Supernatants from TNF-alpha-stimulated A549 cells contained significant concentrations of IL-8, and coincubation of these supernatants with anti-IL-8 decreased supernatant-induced chemotaxis. Finally, coincubation of TNF-alpha with anti-IL-8 during transmigration experiments partially inhibited neutrophil migration through A549 monolayers. Therefore, pulmonary type II epithelial cells facilitate TNF-alpha-induced transcellular migration of neutrophils through the production of soluble protein synthesis-dependent chemotactic factors, including IL-8. These data support the concepts of cytokine networking in inflammatory cell recruitment and an active role for pulmonary epithelium in lung inflammation.