PRODUCTION OF PROINFLAMMATORY CYTOKINES AND INFLAMMATORY MEDIATORS INHUMAN INTESTINAL EPITHELIAL-CELLS AFTER INVASION BY TRICHINELLA-SPIRALIS

Epithelial cells are the first point of host contact for invasive inte stinal pathogens and may initiate mucosal inflammatory responses via p roduction of proinflammatory cytokines and mediators. The aim of the p resent study was to investigate in vitro the initial invasion of a par asitic nematode (Trichinella spiralis), to measure the early productio n of specific epithelial cytokines and inflammatory mediators after in vasion, and to compare these responses with those to invasive bacteria , Monolayers of human colonic epithelial cell lines (HT29, T84, and Ca co-2) were infected by T. spiralis or Listeria monocytogenes. Bile-act ivated infective larvae of T. spiralis invaded and migrated into the e pithelial cell monolayers, leaving trails of dead cells. Transmission electron microscopy studies of damaged cells along the trail showed a progressive increase in size, disruption of cell membranes, loss or di lution of cytoplasmic proteins, and swelling of mitochondria and nucle i, However, no nuclear fragmentation was observed. With reverse transc ription-PCR and an enzyme-linked oligonucleotide chemiluminescent assa y, mRNA transcripts of interleukin-1 beta (IL-1 beta), IL-8, and epith elial neutrophil activating peptide 78 were shown to increase in epith elial cells invaded by T. spiralis or L. monocytogenes, but only L. mo nocytogenes elicited increased inducible nitric oxide synthase (iNOS) mRNA. No increase in tumor necrosis factor alpha or transforming growt h factor beta mRNA was seen after T. spiralis invasion. Increased leve ls of IL-8 were also released from the basolateral surfaces of infecte d monolayers as detected by sandwich enzyme-linked immunosorbent assay . Induction and secretion of proinflammatory cytokines in epithelial c ells after nematode or bacterial invasion may initiate the acute infla mmatory response of the small intestine. The upregulation of iNOS in b acterial infections may contribute to mucosal defense and may also be associated with subsequent cell death, whereas different mechanisms ap pear to operate after nematode invasion.