PMN serine proteases elastase and proteinase-3, but not cathepsin G, decrease TER. Purified PMN elastase, proteinase-3, and cathepsin G (1 U/ml) were added to the basolateral aspect of inverted T84 monolayers cultured on 0.4-μm pore size filters. TER was measured after 30 s of incubation and is expressed as the percentage of the baseline TER at the start of the assay. Values are means ± SEM, n = 3 per group; *, p < 0.05 compared with vehicle control (HBSS). Data were generated from three independent experiments done in duplicate.