Porcine Intestinal Epithelial Cells Initiate an Early Stage Protection Against Escherichia coli K88

Enterotoxigenic Escherichia coli (ETEC) are major intestinal pathogens, resulting in serious diarrhea or even death in animal husbandry. Recent studies mainly focus on exogenous treatment, whereas the internal protective reaction is not fully clarified. In this study, we discovered a defensive response in porcine intestinal epithelial cell line IPEC-J2 against ETEC infection. After 15 minutes challenged with E. coli K88 (multiplicity of infection was 10:1), the transepithelial electrical resistance (TEER) descended (p<0.01), expression of tight junction (TJ) proteins occludin and claudin-1 reduced (p<0.05), and immunofluorescence (IF) showed disassembly of TJs occludin, claudin-1 and zonula occluden (ZO)-1. Meanwhile the TJ restoration was already initiated through increased transcription of occludin (p<0.05), claudin-1 (p<0.001), ZO-1 (p<0.05), and myosin cytoskeleton F-actin (p<0.001). 15 minutes later we detected an elevation in TEER (1.29 fold, p<0.05), upregulation of occludin and claudin-1 (both p<0.05), and relocalization of occludin, claudin-1 and ZO-1, compared with non-infected control. The repaired barrier would gradually diminish in 90 minutes according to observations on TEER, TJ expression, and IF. Interestingly when we eliminated E. coli K88 after 15-minute infection, the rapid response was replaced by a long-term recovery within 120 minutes. In order to elucidate the molecular mechanism, we compared gene expression patterns of non-infected control, 15 min and 60 min after infection using PCR array. Factors in four signaling pathways, including interferon-gamma (IFN-γ), fibroblast growth factors (FGFs), epidermal growth factors (EGFs), gonadotropin-releasing hormone (GnRH), were enhanced (p<0.05) at 15 min. At 60 min, however, majority of those enhanced factors were not differentially expressed compared with non-infected control, suggesting the signaling pathways may be suppressed. Altogether, the intestinal epithelial cells will initiate an immediate protective system to restore the damaged intestinal integrity caused by ETEC. The defensive mechanism works effectively at the early stage and will be blocked as the infection progressing.