Figure 4: Interleukin-6 production by 16-HBE cells, corrected for cell proliferation and expressed as a % of exposure with the corresponding pH without pepsin (control). Interleukin-6 release induced by pepsin is higher at pH 1.5 compared to pH 2.5 (mean difference 283%; ). Data are expressed as means (histograms) and SEM (bars) for 3 replicates. See supplement Figure  2 for induction of IL-6 at all pepsin concentrations and pH levels used in the statistical analysis.