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

Summary 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 adap- tive 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), immunohistochemistryand/orcytometricbeadarray,respectively.Interferon (IFN)-a secretion following cytosine phosphatidyl guanine (CpG) A oligode- oxynucleotide(ODN)2216(5-GGGGGACGATCGTCGGGGGG-3)stimula- tion 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)-a, interleukin (IL)-6 and IL-8 were increased significantly compared with controls. In con- trast, the IFN-a secretion of peripheral blood pDC isolated from flaring IBD, particularlyinUCpatients,wasreducedsignificantlycomparedwithcontrols. Our data suggest an aberrant distribution and function of pDC in IBD, con- trary to their generally implicated role as inducers of tolerance. We speculate that the impaired IFN-a secretion may relate to the hypothesized defect in innate immunity in IBD and could also impact upon the generation of regu- latory T cells (Treg).