Effect of neutrophil elastase (NE) on SLPI in supernatants from cultured A549 cells. A549 cells were cultured for 24 h with NE at the concentrations shown, with an equivalent concentration of the buffer alone, or in a serum free media control. The y axis shows the average of the SLPI secreted in each condition as a percentage of the SLPI secreted by control cells (% SLPI release). Error bars represent standard error of the mean (SEM). N = 3–5 separate experiments for all except buffer control (N = 2). A dose-related reduction in SLPI supernatant concentration was seen with NE (statistically significant from 2.5 nM) (p = 0.006, one way ANOVA).