In vitro study of the induction of cytokine production and the secretion of mucinases by mucous-producing atypical EPEC strains

Abstract

Enteropathogenic Escherichia coli (EPEC) are important bacterial agents of diarrhea in developing countries and produce characteristic intestinal histopathological lesions. Typical EPEC strains carry a virulence plasmid (EPEC adherence factor) that is absent in atypical EPEC. Our group has demonstrated that atypical EPEC have more diverse phenotypic characteristics and virulence determinants than typical EPEC, and some of these strains present unusual properties such as the ability to induce a significant increase in mucus production on ligated rabbit ileal loops in vivo, and to induce the transcription of mucin-encoding genes in goblet cells and human enterocytes in culture. Mucins, synthesized and secreted by goblet cells, are major glicoprotein constitutents of mucus that act in defense against external stimuli such as mechanical injury, chemicals and infections by pathogens. Several pathogens stimulate mucus production in their interaction with different host epithelia by altering mucin-encoding genes expression in goblet cells. Several reports also point out that the adaptive immune response seems to modulate goblet cells, and their activation mediated by IL- 1, IL- 4, IL- 6, IL- 8, IL -13 and TNF- ± has been demonstrated on intestinal cells in vitro and/or in vivo animal models. Altough mucus production increases the intestinal mucosa protection, some microorganisms secrete proteases that cleave specific mucins, favoring their approximation to host cells receptors. Recent reports indicate that atypical EPEC are emerging pathogens, so there is a need to further study of their interaction with the host and the occurrence of new virulence mechanisms. The mechanisms that induce increased production of mucus by some atypical EPEC strains are not yet determined. Nor is it known whether these bacteria produce mucinases. This study was designed to examine the interference caused by two atypical EPEC strains that induce mucus production in TNF- ±, IL-1 b and IL-8 in human enterocytic lines (LS174T and Caco-2 cells). Furthermore, the ability to use mucus as a substrate will be evaluated through the analysis of mucinases production in a selected atypical EPEC strains collection.