Introduction: Migration of neutrophils across the intestinal epithelium is the hallmark of inflammatory conditions of the bowel. In cultured intestinal epithelial monolayer models, neutrophils can be induced to migrate along a chemotactic gradient such as n-formyl-methionyl-leucyl-phenylalanine (fMLP). Physical passage of the neutrophils across the epithelium could disrupt the tight-junctions, possibly leading to a large increase in the transepithelial conductance (Gt). The goal of this study is to determine whether transepithelial migration of neutrophils induced by enteropathogenic Escherichia coli (EPEC) causes changes in Gt comparable with those seen with fMLP.
Methods: The apical side of T84 monolayers were rapidly infected with EPEC E2348/69 or exposed to 1μM fMLP. A third group of monolayers exposed to neither EPEC nor fMLP served as control. Indium-labeled neutrophils were added to the serosal side of monolayers grown on a cell culture insert membrane (12 μm pores). Gt was measured at fixed intervals up to 4 hours. After a 150-minute incubation, radioactivity of the neutrophils that migrated to the apical side was assayed and the number of migrating neutrophils was calculated.
Results: At 150 minutes, EPEC induced similar neutrophil chemotactic capability compared to fMLP (231 ± 34 · 103 and 193 ± 48 · 103, respectively, n = 13, P > 0.05). However, EPEC-induced neutrophil migration was not associated with significant increase in Gt, 1.13 ± 0.16 fold of baseline Gt, in distinction with fMLP groups, 13.3 ± 0.48 fold, n = 7 (P < 0.05). Gt changes with EPEC were seen after 4 hours of infection, but were not different in the presence or absence of neutrophil migration (1.37 ± 0.12 fold and 1.42 ± 0.17 fold of baseline Gt, respectively).
Conclusions: The results indicate that EPEC-induced neutrophil migration can occur without significant disruption of barrier function. In addition, the chemo-attractant recruiting neutrophils during EPEC infection is unlikely to be fMLP; and, the Gt increase seen with fMLP-driven recruitment may indicate a discretionary compromise of barrier function during neutrophil migration.