부산대학교 도서관

ABSTRACTAlthough the probiotic Escherichia colistrain Nissle 1917 has been proven to be efficacious for the treatment of inflammatory bowel diseases, the underlying mechanisms of action still remain elusive. The aim of the present study was to analyze the effects of E. coliNissle 1917 on cell cycling and apoptosis of peripheral blood and lamina propria T cells (PBT and LPT, respectively). Anti-CD3-stimulated PBT and LPT were treated with E. coliNissle 1917-conditioned medium (E. coliNissle 1917-CM) or heat-inactivated E. coliNissle 1917. Cyclin B1, DNA content, and caspase 3 expression were measured by flow cytometry to assess cell cycle kinetics and apoptosis. Protein levels of several cell cycle and apoptosis modulators were determined by immunoblotting, and cytokine profiles were determined by cytometric bead array. E. coliNissle 1917-CM inhibits cell cycling and expansion of peripheral blood but not mucosal T cells. Bacterial lipoproteins mimicked the effect of E. coliNissle 1917-CM; in contrast, heat-inactivated E. coliNissle 1917, lipopolysaccharide, or CpG DNA did not alter PBT cell cycling. E. coliNissle 1917-CM decreased cyclin D2, B1, and retinoblastoma protein expression, contributing to the reduction of T-cell proliferation. E. coliNissle 1917 significantly inhibited the expression of interleukin-2 (IL-2), tumor necrosis factor α, and gamma interferon but increased IL-10 production in PBT. Using Toll-like receptor 2 (TLR-2) knockout mice, we further demonstrate that the inhibition of PBT proliferation by E. coliNissle 1917-CM is TLR-2 dependent. The differential reaction of circulating and tissue-bound T cells towards E. coliNissle 1917 may explain the beneficial effect of E. coliNissle 1917 in intestinal inflammation. E. coliNissle 1917 may downregulate the expansion of newly recruited T cells into the mucosa and limit intestinal inflammation, while already activated tissue-bound T cells may eliminate deleterious antigens in order to maintain immunological homeostasis.