Constitutive and regulated secretion of secretory leukocyte proteinase inhibitor by human intestinal epithelial cells

Background & Aims: Epithelial cells participate in immune regulation and mu cosal integrity by generating a range of biologically active mediators. In the intestine, little is known about the potential endogenous antiinflammat ory molecules. Secretory leukocyte proteinase inhibitor (SLPI) is a major s erine proteinase inhibitor, a potent antibiotic, and thus a potential antii nflammatory molecule, although it is not known if it is secreted by intesti nal epithelial cells. Methods: We show, by reverse-transcription polymerase chain reaction, the presence of SLPI messenger RNA in human model intestin al epithelial cell lines (Caco2-BBE, T84, and HT29-Cl.19A) and human jejunu m and colon biopsy specimens. The polymerase chain reaction product was clo ned and sequenced and is identical to that of SLPI isolated previously from the human parotid gland. Results: As analyzed by enzyme-linked immunosorbe nt assay, the constitutive secretion of SLPI occurs in a markedly polarized manner toward the apical surface and is enhanced by inflammatory mediators including tumor necrosis factor alpha and interleukin 1 beta (approximate to 3.5-fold increase over control value). SLPI release is also stimulated b y activation of protein kinase C isoenzymes, but not by activation of adeno sine 3',5'-cyclic monophosphate- or Ca2+-regulated signaling molecules. SLP I protein is detectable in intestinal lavage fluids collected from normal a dult humans. Recombinant SLPI attenuates digestive enzyme (trypsin)- or leu kocyte proteinase (elastase)-induced permeability alteration of a model epi thelia in a dose-dependent manner. Moreover, SLPI exhibits an antibacterial activity against at least one major intestinal pathogen, Salmonella typhim urium. In contrast, SLPI does not influence epithelial barrier integrity as assessed by transepithelial conductance measurements or electrogenic ion t ransport. Conclusions: These results establish that human intestinal epithe lium expresses and apically secretes SLPI, a molecule that may significantl y contribute to the protection against attack from inflammatory cells and d igestive enzymes, as well as against microbial infection.