Abnormal activity of innate immune cells and T-helper (Th) 17 cells has been implicated in the pathogenesis of autoimmune and inflammatory diseases, including Crohn's disease (CD). Intestinal innate immune (myeloid) cells have been found to induce development of Th17 cells in mice, but it is not clear if this occurs in humans or in patients with CD. We investigated whether human intestinal lamina propria cells (LPCs) induce development of Th17 cells and whether these have a role in the pathogenesis of CD.
Normal intestinal mucosa samples were collected from patients with colorectal cancer and noninflamed and inflamed regions of mucosa were collected from patients with CD. LPCs were isolated by enzymatic digestion and analyzed for expression of HLA-DR, lineage markers CD14 and CD163 using flow cytometry.
Among HLA-DR(high) Lin(-) cells, we identified a subset of CD14(+) CD163(low) cells in intestinal LPCs; this subset expressed Toll-like receptor (TLR) 2, TLR4, and TLR5 mRNAs and produced interleukin (IL)-6, IL-1β, and tumor necrosis factor in response to lipopolysaccharide. In vitro co-culture with naïve T cells revealed that CD14(+) CD163(low) cells induced development of Th17 cells. CD14(+) CD163(low) cells from inflamed regions of mucosa of patients with CD expressed high levels of IL-6, IL-23p19, and tumor necrosis factor mRNAs, and strongly induced Th17 cells. CD14(+) CD163(low) cells from the noninflamed mucosa of patients with CD also had increased abilities to induce Th17 cells compared with those from normal intestinal mucosa.
CD14(+) CD163(low) cells in intestinal LPCs from normal intestinal mucosa induce differentiation of naive T cells into Th17 cells; this activity is increased in mucosal samples from patients with CD. These findings show how intestinal myeloid cell types could contribute to pathogenesis of CD and possibly other Th17-associated diseases.
Copyright © 2013 AGA Institute. Published by Elsevier Inc. All rights reserved.

Human dendritic cells (DC) can be differentiated from blood monocytes in the presence of GM-CSF and IL-4 and matured by lipopolysaccharide (LPS). Vitamin D3 inhibits the maturation of human DC measured by changes in surface expression of HLA-DR, CD14, CD40, CD80, CD83, and CD86. We here examine the function of vitamin D3 during DC maturation. One of the earliest changes to LPS-induced maturation was an increase in CD83 expression. Vitamin D3 inhibited the increase in expression of HLA-DR, CD40, CD80, CD83, and CD86 and the decrease in expression of CD14, which was paralleled morphologically by vitamin D3-induced inhibition of dendritic cell differentiation. Vitamin D3 acted in synergy with the TLR agonists LPS and peptidoglycan (PGN) in inducing IL-6, IL-8, and IL-10, whereas vitamin D3 completely inhibited LPS-induced secretion of IL-12. The synergy occurred at concentrations where neither vitamin D3 nor the TLR agonists alone induced measurable cytokine secretion. Both LPS and PGN enhanced the level of the vitamin D3 receptor (VDR). Taken together, these data demonstrated that vitamin D3 and TLR agonists acted in synergy to alter secretion of cytokines from human DC in a direction that may provide an anti-inflammatory environment.

Atopic dermatitis (AD) is a common skin disease associated with a T(H)2 response and increased levels of T(H)2-associated cytokines and IgE. The mechanisms resulting in skewing the immune response in a T(H)2 direction in AD are not fully elucidated. However, such skewing has recently been associated with IL-25 in a murine model for allergic airway disease. The aim of this study was to investigate whether IL-25 may have a role in AD. We have identified IL-25-producing cells within the dermis of AD patients and propose that these cells are dendritic cells (DCs). This is supported by in vitro experiments that indicate that monocyte-derived DCs are capable of producing IL-25. As null mutations of filaggrin are associated with the development of an impaired skin barrier in AD, we investigated whether IL-25 affects filaggrin synthesis by keratinocytes. Using mRNA analysis, we have shown that IL-25 stimulation does indeed decrease filaggrin synthesis in cultured keratinocytes. These results suggest that IL-25 produced by DCs could have a dual role as both an inducer of the T(H)2 response and as an inhibitor of filaggrin synthesis, thereby directly affecting skin barrier function in AD patients.

Protease-activated receptors (PARs) are a family of G protein-coupled receptors that are activated by serine protease-mediated proteolytic cleavage of their extracellular domain. We have previously characterized the expression and function of PARs in human monocytes and macrophages, yet information about PARs in dendritic cells (DC) is scarce. Monocyte-derived immature DC do not express PARs. Upon maturation with LPS, but not with TNF-alpha or CD40 ligand, DC express PAR1 and PAR3, but not PAR2 or PAR4. Stimulation of DC with the serine protease thrombin or PAR1-activating peptide elicits actin polymerization and concentration-dependent chemotactic responses in LPS-, but not in TNF-alpha-matured DC. The thrombin-induced migration is a true chemotaxis with only negligible chemokinesis. Stimulation of PARs with thrombin or the respective receptor-activating peptides activates ERK1/2 and Rho kinase as well as subsequent phosphorylation of the regulatory myosin L chain 2. The ERK1/2- and Rho kinase 1-mediated phosphorylation of myosin L chain 2 was indispensable for the PAR-mediated chemotaxis as shown by pharmacological inhibitors. Additionally, thrombin stimulated the Rho-dependent release of the CC chemokine CCL18/pulmonary and activation-regulated chemokine, which induces chemotaxis of lymphocytes and immature DC as well as fibroblast proliferation. The colocalization of CD83(+) DC with CCL18 in human atherosclerotic plaques revealed by immunofluorescence microscopy combined with the presence of functionally active thrombin receptors on mature DC point to a previously unrecognized functional role of thrombin in DC biology. The thrombin-induced stimulation of mature DC may be of particular relevance in atherosclerotic lesions, which harbor all components of this novel mechanism.