Effects of IL-8 and PMN transmigration on PCPEC barrier function. The inverted Transwell system used to investigate PMN transmigration is displayed in (A). (B, C) Effects of IL-8 or PMN transmigration on barrier function were measured by TEER (B) and TR-dextran flux (C) of PCPEC monolayers. IL-8 (10 ng/ml) was applied to the lower compartment, and PMNs (PCPECs:PMNs ratio 1:10) to the apical compartment of inverted PCPEC cultures or PMNs and IL-8 in combination. The TEER results are expressed as absolute TEER values (Ω × cm2) and were measured before and after 4 h of PMN transmigration. TR-dextran flux was determined in the basolateral-to-apical direction (upper to lower compartment) after 4 h of incubation and is expressed as percentage of tracer in the basolateral compartment. Data are shown are mean ± SD for four independent experiments, each performed in triplicate.