Aberrant plasmacytoid dendritic cell distribution and function in patients with Crohn's disease and ulcerative colitis.

Dendritic cell (DC) function is believed to be of critical importance for the pathogenesis of inflammatory bowel disease (IBD). To date, most research in animal models and the few human data available is restricted to myeloid DC, while plasmacytoid DC (pDC) capable of controlling both innate and adaptive immune responses have not yet been investigated systematically in human Crohn's disease (CD) or ulcerative colitis (UC). CD11c(-) , CD303(+) /CD304(+) and CD123(+) pDC from peripheral blood (n = 90), mucosal tissue (n = 28) or mesenteric lymph nodes (n = 40) (MLNs) of patients with UC and CD or controls were purified and cultured. Thereafter, pDC were enumerated, phenotyped and cytokine secretion measured by flow cytometry (FACS), immunohistochemistry and/or cytometric bead array, respectively. Interferon (IFN)-α secretion following cytosine phosphatidyl guanine (CpG) A oligodeoxynucleotide (ODN) 2216 (5'-GGGGGACGATCGTCGGGGGG-3') stimulation was assessed by enzyme-linked immunosorbent assay (ELISA). We found a significantly higher frequency of pDC in the inflamed colonic mucosa and MLN of IBD patients. Moreover, the fraction of CD40 and CD86 expressing cultured peripheral blood pDC was significantly higher in flaring UC and CD patients and their secretion of tumour necrosis factor (TNF)-α, interleukin (IL)-6 and IL-8 were increased significantly compared with controls. In contrast, the IFN-α secretion of peripheral blood pDC isolated from flaring IBD, particularly in UC patients, was reduced significantly compared with controls. Our data suggest an aberrant distribution and function of pDC in IBD, contrary to their generally implicated role as inducers of tolerance. We speculate that the impaired IFN-α secretion may relate to the hypothesized defect in innate immunity in IBD and could also impact upon the generation of regulatory T cells (T(reg) ).

Saccharomyces boulardii inhibits lipopolysaccharide-induced activation of human dendritic cells and T cell proliferation.

Saccharomyces boulardii (Sb) is a probiotic yeast preparation that has demonstrated efficacy in inflammatory and infectious disorders of the gastrointestinal tract in controlled clinical trials. Although patients clearly benefit from treatment with Sb, little is known on how Sb unfolds its anti-inflammatory properties in humans. Dendritic cells (DC) balance tolerance and immunity and are involved critically in the control of T cell activation. Thus, they are believed to have a pivotal role in the initiation and perpetuation of chronic inflammatory disorders, not only in the gut. We therefore decided to investigate if Sb modulates DC function. Culture of primary (native, non-monocyte-derived) human myeloid CD1c+CD11c+CD123(-) DC (mDC) in the presence of Sb culture supernatant (active component molecular weight < 3 kDa, as evaluated by membrane partition chromatography) reduced significantly expression of the co-stimulatory molecules CD40 and CD80 (P < 0.01) and the DC mobilization marker CC-chemokine receptor CCR7 (CD197) (P < 0.001) induced by the prototypical microbial antigen lipopolysaccharide (LPS). Moreover, secretion of key proinflammatory cytokines such as tumour necrosis factor-alpha and interleukin (IL)-6 were notably reduced, while the secretion of anti-inflammatory IL-10 increased. Finally, Sb supernatant inhibited the proliferation of naive T cells in a mixed lymphocyte reaction with mDC. In summary, our data suggest that Sb may exhibit part of its anti-inflammatory potential through modulation of DC phenotype, function and migration by inhibition of their immune response to bacterial microbial surrogate antigens such as LPS.

Exaggerated inflammatory response of primary human myeloid dendritic cells to lipopolysaccharide in patients with inflammatory bowel disease.

Inflammatory bowel disease (IBD) results from a breakdown of tolerance towards the indigenous flora in genetically susceptible hosts. Failure of dendritic cells (DC) to interpret molecular microbial patterns appropriately when directing innate and adaptive immune responses is conceivable. Primary (conventional, non-monocyte generated) CD1c(+)CD11c(+)CD14(-)CD16(-)CD19(-) myeloid blood or mucosal dendritic cells (mDC) from 76 patients with Crohn's disease (CD) or ulcerative colitis (UC) in remission, during flare-ups (FU) and 76 healthy or non-IBD controls were analysed by fluorescence activated cell sorter (FACS) flow cytometry and real-time polymerase chain reaction. Cytokine secretion of freshly isolated, cultured and lipopolysaccharide (LPS)-stimulated highly purified mDC (purity >95%) was assessed using cytometric bead arrays (CBA). More cultured and stimulated circulating mDC express CD40 in IBD patients. Stimulated circulating mDC from IBD patients secrete significantly more tumour necrosis factor (TNF)-alpha and interleukin (IL)-8. Toll-like receptor (TLR)-4 expression by mDC was higher in remission and increased significantly in flaring UC and CD patients compared with remission (P < 0.05) and controls (P < 0.001). Fluorochrome-labelled LPS uptake by mDC was evaluated at different time-points over 24 h by measuring mean fluorescence intensity (MFI). Circulating mDC from IBD patients take up more LPS and the uptake begins earlier compared with controls (P < 0.05 in CD-FU and UC-FU at 24 h). The frequency of mucosal mDC (P < 0.05) and the number of CD40 expressing mucosal mDC is significantly greater in UC and CD compared with non-IBD controls (P < 0.001 versus P < 0.01, respectively). Our data suggest an aberrant LPS response of mDC in IBD patients, resulting in an inflammatory phenotype and possibly intestinal homing in acute flares.