Successful granulocyte‐colony stimulating factor treatment of Crohn's disease is associated with the appearance of circulating interleukin‐10‐producing T cells and increased lamina propria plasmacytoid dendritic cells

Granulocyte‐colony stimulating factor (G‐CSF) has proved to be a successful therapy for some patients with Crohn's disease. Given the known ability of G‐CSF to exert anti‐T helper 1 effects and to induce interleukin (IL)‐10‐secreting regulatory T cells, we studied whether clinical benefit from G‐CSF therapy in active Crohn's disease was associated with decreased inflammatory cytokine production and/or increased regulatory responses. Crohn's patients were treated with G‐CSF (5 µg/kg/day subcutaneously) for 4 weeks and changes in cell phenotype, cytokine production and dendritic cell subsets were measured in the peripheral blood and colonic mucosal biopsies using flow cytometry, enzyme‐linked immunosorbent assay and immunocytochemistry. Crohn's patients who achieved a clinical response or remission based on the decrease in the Crohn's disease activity index differed from non‐responding patients in several important ways: at the end of treatment, responding patients had significantly more CD4⁺ memory T cells producing IL‐10 in the peripheral blood; they also had a greatly enhanced CD123⁺ plasmacytoid dendritic cell infiltration of the lamina propria. Interferon‐γ production capacity was not changed significantly except in non‐responders, where it increased. These data show that clinical benefit from G‐CSF treatment in Crohn's disease is accompanied by significant induction of IL‐10 secreting T cells as well as increases in plasmacytoid dendritic cells in the lamina propria of the inflamed gut mucosa.     

Pathogenic T cell subsets in allergic and chronic inflammatory bowel disorders

Homeostasis in the gastrointestinal tract relies on a sensitive equilibrium between permissive and protective functions. This is closely reflected in the regulation of the intestinal immune system and especially T cells in the gut. This balance, however, is susceptible to disturbances as demonstrated by pathological conditions like food allergy, celiac disease, or inflammatory bowel disease. In these allergic and chronic inflammatory bowel disorders, luminal antigens get access to the lamina propria where they trigger a dysregulated immune response with crucial involvement of different T cell subsets. We will begin this review with some comprehensive remarks on current concepts on the pathogenesis of these diseases before taking a closer look at the life cycle of intestinal T cells consisting of priming, homing, differentiation and proliferation and apoptosis respectively. Subsequently we will discuss the specific implication of distinct T cell subsets in allergic and chronic inflammatory conditions of the gastrointestinal tract in detail and comment on current and future approaches to targeted therapy in this context.     

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‐α 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.     

Involvement of plasmacytoid dendritic cells in human diseases

In vitro studies have reported that plasmacytoid dendritic cells (PDCs) exert multiple functions, including production of interferon (IFN)-alpha as effector cells and regulation of T-cell responses as mature DCs. Here we review recent data obtained in situ showing that PDCs accumulate in lesions of type I IFN-related disorders (virus infections and lupus erythematosus), Th2 cell-dominated allergic reactions, and ovarian carcinoma. These results demonstrate that PDCs do migrate to peripheral tissues during inflammation, which lends further support to the view that PDCs most likely are important players in innate and adaptive immunity in vivo. Future research should aim at defining the exact pathogenic or defense roles of PDCs in such disorders and determine whether these cells are potential targets for therapeutic intervention in microbial infections, allergy, autoimmunity, or cancer.     

Cytologic features and frequency of plasmacytoid dendritic cells in the lymph nodes of patients with histiocytic necrotizing lymphadenitis (Kikuchi‐Fujimoto disease)

Histiocytic necrotizing lymphadenitis (HNL), also known as Kikuchi‐Fujimoto disease, is a benign and self‐limiting disease. It is histologically characterized by nodal lesions that show the infiltration of histiocytes, lymphoid cells, myeloid dendritic cells (mDCs), and plasmacytoid dendritic cells (pDCs), along with either apoptotic or karyorrhexic nuclear debris. pDCs have been proposed to be lymphoid early‐committed immature DCs which are positive for CD123, CD303, CD68, and HLA‐DR but negative for fascin, a mature DC marker, as well as CD13 and CD33,which are mDC markers. In the present study, we analyzed the cytomorphologic features and frequency of pDCs in the lymph nodes of HNL patients. Because the cytologic apprearance of pDCs with Papanicolau staining was quite similar to that of large lymphocytes, immunocytochemistry against CD123 was necessary for the distinction of pDCs. Counting the number of CD123‐positive pDCs in the HNL lymph nodes revealed that pDCs more frequently infiltrated the lymph nodes in the setting of HNL than in either reactive lymphadenitis or T and B cell lymphoma. In addition, interestingly, the numberof pDCs did not depend on the age of the HNL lesion, thus suggesting that pDCs are excellent indicators for the cytologic diagnosis of HNL. Diagn. Cytopathol. 2010. © 2009 Wiley‐Liss, Inc.     

Role of plasmacytoid dendritic cell subsets in allergic asthma

Plasmacytoid dendritic cells (pDCs) are major type‐I interferon‐producing cells that play important roles in antiviral immunity and tolerance induction. These cells share a common DC progenitor with conventional DCs, and Fms‐like tyrosine kinase‐3 ligand is essential for their development. Several subsets of pDCs have been identified to date including CCR9⁺, CD9⁺, and CD2⁺ pDCs. Recently, three subsets of pDCs were described, namely CD8α⁻β⁻, CD8α⁺β⁻, and CD8α⁺β⁺ subsets. Interestingly, CD8α⁺β⁻ and CD8α⁺β⁺ but not CD8α⁻β⁻ pDCs were shown to have tolerogenic effects in experimentally induced allergic asthma. These tolerogenic effects were shown to be mediated by the generation of FOXP3⁺ regulatory T cells through retinoic acid and the induction of retinaldehyde dehydrogenase enzymes. These newly described subsets of pDCs show high potentials for novel therapeutic approaches for the treatment of allergic diseases. In this review, we will address the new progress in our understanding of pDC biology with respect to allergic disease, in particular allergic asthma.     

Dendritic cell subsets in lymph nodes are characterized by the specific draining area and influence the phenotype and fate of primed T cells

Dendritic cells (DC) are important in differential T-cell priming. Little is known about the local priming by DC in the microenvironment of different lymph nodes and about the fate of the imprinted T cells. Therefore, freshly isolated rat DC from mesenteric lymph nodes (mLN) and axillary lymph nodes (axLN) were phenotyped and cultured with blood T cells in the presence of the superantigen Mycoplasma arthritidis mitogen (MAM). The phenotype, proliferation and apoptosis of the primed T cells were analysed. Our data show that a common DC population exists in both mLN and axLN. In addition, region-specific DC with an organotypical marker expression imprinted by the drained area were found. Coculture of T cells with DC from mLN or axLN resulted in a distinct shift in the CD4 and CD8 expression of T cells and their phenotype. Furthermore, when these differentially primed mLN and axLN T cells were injected into recipients, mLN-primed T cells survived longer in other lymphoid organs. The results show that the region-specific DC have a unique phenotype and an impact on the ratio of CD4 : CD8 T cells during an immune response in vivo.     

Prostaglandin E2 is a negative regulator on human plasmacytoid dendritic cells

Prostaglandin E2 (PGE2), a major lipid derived from the metabolism of arachidonic acid, is an environmentally bioactive substance produced by inflammatory processes and acts as a cAMP up-regulator that plays an important role in immune responses. It has been reported that PGE2 has the ability to inhibit the production of interleukin-12 by myeloid dendritic cells (MDCs) and macrophages, and then induce preferential T helper type 2 (Th2) cell responses. However, little is known of the function of PGE2 for plasmacytoid dendritic cells (PDCs), which may contribute to the innate and adaptive immune response to viral infection, allergy and autoimmune diseases. In the present study, we compared the biological effect of PGE2 on human PDCs and MDCs. PGE2 caused the death of PDCs but MDCs survived. Furthermore, we found that, whereas PGE2 inhibited interferon-alpha production by PDCs in response to virus or cytosine-phosphate-guanosine, it inhibited interleukin-12 production by MDCs in response to lipopolysaccharide (LPS) or poly(I:C). Although both virus-stimulated PDCs and LPS-stimulated MDCs preferentially induced the development of interferon-gamma-producing Th1 cells, pretreatment with PGE2 led both DC subsets to attenuate their Th1-inducing capacity. These findings suggest that PGE2 represents a negative regulator on not only MDCs but also PDCs.     

Immune functions and recruitment of plasmacytoid dendritic cells in psoriasis

Psoriasis is one of the most common chronic T cell-mediated diseases in humans. Among the most proximal event in the innate immunity cascade driving psoriatic inflammation is the secretion of type I IFN by activated plasmacytoid dendritic cells (pDC), a special DC subset strategically positioned in pre-psoriatic symptomless skin. There is an IFN-α signature in primary psoriatic plaques, and blocking of type I IFN signalling can prevent the expansion of pathogenetic T cells and development of psoriatic phenotype. Recently, we have demonstrated that pDC infiltration in psoriatic skin correlates with the expression of markers typical of early phases of psoriasis, whereas it is almost absent in long-lasting lesions. Importantly, pDC recruitment in psoriatic skin is strictly associated with the chemerin/ChemR23 axis, and is temporally active during psoriatic plaque development. Pro-chemerin is produced primarily by dermal fibroblasts, but also by mast cells and endothelial cells. Once secreted, it can be activated by enzymes produced by neutrophils and mast cells, which infiltrate early psoriasis lesions. These findings propose the chemerin/ChemR23 axis as a potential novel therapeutic target in psoriasis.     

Human hepatic lymph nodes contain normal numbers of mature myeloid dendritic cells but few plasmacytoid dendritic cells

We investigated whether the hyporesponsiveness of the adaptive arm of the liver immune system is related to the composition of the dendritic cell (DC) population in hepatic lymph nodes. Noninflamed human hepatic lymph nodes (LN) were obtained from multiorgan donors, inflamed hepatic LN from liver transplant recipients with autoimmune cholestatic liver diseases, and inguinal LN from kidney transplant recipients. Quantitative immunohistochemistry showed that all three types of LN contained comparable numbers of mature and immature myeloid DC, but that noninflamed and inflamed hepatic LN contained significantly fewer plasmacytoid DC as compared to inguinal LN. Likewise, DC-enriched cell preparations from hepatic LN contained relatively few plasmacytoid DC. The difference in numbers of plasmacytoid DC was confirmed in comparisons of hepatic LN and ileacal LN from the same organ-donors. Myeloid DC from hepatic LN showed similar expressions of HLA-DR, CD83, and CD86, and higher expression of CD80 compared to myeloid DC from inguinal LN. In conclusion, hepatic LN contain similar numbers of myeloid DC as muscle/skin lymph-draining LN, with no signs of immaturity, but relatively few plasmacytoid DC.     

Anti‐atherogenic peptide Ep1.B derived from apolipoprotein E induces tolerogenic plasmacytoid dendritic cells

Tolerogenic dendritic cells (DCs) play a critical role in the induction of regulatory T cells (T_regs), which in turn suppress effector T cell responses. We have previously shown the induction of DCs from human and mouse monocytic cell lines, mouse splenocytes and human peripheral blood monocytes by a novel apolipoprotein E (ApoE)‐derived self‐peptide termed Ep1.B. We also showed that this C‐terminal region 239–252 peptide of ApoE has strong anti‐atherogenic activity and reduces neointimal hyperplasia after vascular surgery in rats and wild‐type as well as ApoE‐deficient mice. In this study, we explored the phenotype of DC subset induced by Ep1.B from monocytic cell lines and from the bone marrow‐derived cells. We found Ep1.B treatment induced cells that showed characteristics of plasmacytoid dendritic cells (pDC). We explored in‐vitro and in‐vivo effects of Ep1.B‐induced DCs on antigen‐specific T cell responses. Upon in‐vivo injection of these cells with antigen, the subsequent ex‐vivo antigen‐specific proliferation of lymph node cells and splenocytes from recipient mice was greatly reduced. Our results suggest that Ep1.B‐induced pDCs promote the generation of T_reg cells, and these cells contribute to the induction of peripheral tolerance in adaptive immunity and potentially contribute its anti‐atherogenic activity.     

Recruitment of immature plasmacytoid dendritic cells (plasmacytoid monocytes) and myeloid dendritic cells in primary cutaneous melanomas

The present study has analysed the distribution and phenotype of dendritic cells (DCs) in primary cutaneous melanomas and sentinel lymph nodes by immunohistochemistry. In primary melanomas, an increase of DCs was found in the epidermis and the peritumoural area. Intraepidermal DCs were mostly CD1a⁺/Langerin⁺ Langerhans cells. Peritumoural DCs included a large population of DC‐SIGN⁺/mannose‐receptor⁺/CD1a^? DCs, a small subset of CD1a⁺ DCs, and, remarkably, plasmacytoid monocytes/plasmacytoid DCs (PM/PDCs). The PM/PDCs, most likely recruited by SDF‐1 secreted by melanoma cells, produced type I interferon (IFN‐I), but the expression of the IFN‐α inducible protein MxA was extremely variable and very limited in the majority of cases. All DC subsets were predominantly immature. The peritumoural area also contained a minor subset of mature CD1a⁺ DCs. However, the small amount of local interleukin (IL)‐12 p40 mRNA and the naïve phenotype of 20–50% of peritumoural T‐lymphocytes are consistent with poor T‐cell stimulation or erroneous recruitment. In sentinel lymph nodes, notable expansion of mature CD1a⁺/Langerin⁺ DCs was observed. The paucity of intratumoural DCs and the predominant immature phenotype of peritumoural dermal DCs indicate defective maturation of primary cutaneous melanoma‐associated DCs, resulting in lack of T‐cell priming. These results may explain why melanoma cells grow despite the presence of infiltrating immune cells. Copyright © 2003 John Wiley & Sons, Ltd.     

Recruitment of myeloid and plasmacytoid dendritic cells in cervical mucosa during Chlamydia trachomatis infection

The mobilization of myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) to the cervix during chlamydial infection is not fully understood, and the role of these cells in immunopathogenesis is largely unknown. As an effective vaccine to control chlamydial infection is currently unavailable, understanding the regulation of the local immune response becomes a necessity. Therefore, mDC and pDC populations were analysed in peripheral blood and cervical samples of controls and Chlamydia -positive women, with or without mucopurulent cervicitis (MPC). Cervical cytokines and C-reactive protein levels in serum were quantified by ELISA and the chlamydial infectious load by culture. Chlamydia trachomatis infection mobilized both mDCs and pDCs to the cervical mucosa. pDCs were recruited more often in women with MPC (p <0.05) and they correlated significantly with the chlamydial load, C-reactive protein levels and cervical interleukin-8 (IL-8) levels. Upregulation of surface expression of co-stimulatory molecules (CD80, CD83 and CD86) on cervical mDCs and pDCs was observed during chlamydial infection but was significant only for mDCs. Significantly higher levels of IL-1β, IL-6 and IL-8 were observed in Chlamydia- positive women with MPC; however, after therapy, IL-8 levels decreased significantly. Median numbers of mDCs after therapy were significantly higher in the cervix and blood of infected women as compared to the numbers of pDCs, which were found to be lower in the cervix after therapy. These results thus suggest that during chlamydial infection, both mDCs and pDCs are recruited to the cervix, but their number and possible immunological functions may differ with the pathological condition. pDCs were associated more often with MPC and inflammatory factors, suggesting that they may possibly be involved in the immunopathogenesis of infections due to Chlamydia .     

Dendritic cells in remodeling of lymph nodes during immune responses

A critical hallmark of adaptive immune responses is the rapid and extensive expansion of lymph nodes. During this process, the complex internal structure of the organs is maintained revealing the existence of mechanisms able to balance lymph node integrity with structural flexibility. This article reviews the extensive architectural remodeling that occurs within lymph nodes during adaptive immune responses and how it is regulated by dendritic cells (DCs). In particular we focus on previously unappreciated functions of DCs in coordinating remodeling of lymph node vasculature, expansion of the fibroblastic reticular network and maintenance of lymphoid stromal phenotypes. Our increased understanding of these processes indicates that DCs need to be viewed not only as key antigen-presenting cells for lymphocytes but also as broad-acting immune sentinels that convey signals to lymphoid organ stroma and thereby facilitate immune response initiation at multiple levels.     

Innate mucosal‐associated invariant T (MAIT) cells are activated in inflammatory bowel diseases

Inflammatory bowel diseases are characterized by a deregulated immune response targeting the gut bacterial flora. Mucosal‐associated invariant T (MAIT) cells are major histocompatibility complex (MHC) class Ib‐restricted innate‐like lymphocytes with anti‐bacterial functions. They display an effector/memory phenotype and are found in large numbers in the blood, mucosae and liver. They have also been implicated in inflammatory diseases such as multiple sclerosis. Therefore, we aimed to analyse the possible involvement of MAIT cells in Crohn's disease (CD) and ulcerative colitis (UC). To this end, a phenotypical and functional analysis of MAIT cells isolated from the blood of healthy subjects, CD and UC patients was undertaken. MAIT cells were also quantified in ileal biopsies of CD patients. The frequency of blood MAIT cells was specifically reduced in IBD patients compared with healthy donors, whereas it was dramatically greater in the inflamed versus healthy tissue. MAIT cells were activated as they expressed significantly more the Ki67 antigen, and this was accompanied by phenotypical changes such as increased expression of natural killer (NK)G2D and B and T lymphocyte attenuator (BTLA). Finally, in‐vitro‐activated MAIT cells from CD and UC patients secreted significantly more interleukin (IL)‐17, together with a decreased interferon (IFN)‐γ in CD but an increased IL‐22 in UC. These data show that MAIT cells are activated in IBD, which results in an increased recruitment towards the inflamed tissues, an altered phenotype and a switch in the pattern of cytokine secretion. This is the first demonstration that MAIT cells are immune players in IBD, whose precise functions in this context need to be addressed.     

The superantigen-induced polarization of T cells in rat peripheral lymph nodes is influenced by genetic polymorphisms in the IL-4 and IL-6 gene clusters

In recent years, it has become clear that the polarization of T cells depends on the genetic background. However, due to the complexity of the genetic background of each animal, a direct comparison of the phenotype is difficult. In this study, a new rat strain LEW.BN-4-10 carrying the chromosomal regions on chromosomes 4 and 10, which harbor IL-6 and IL-4 gene clusters of BN, has been bred on the genetic background of LEW. It was asked whether these two gene clusters influence the polarization of T cell responses. As a model, the Mycoplasma arthritidis mitogen (MAM)-induced inflammation was used focusing on the microenvironment of the draining lymph node (LN). The effect of differences in these regions was tested by comparing LEW.BN-4-10 and LEW rats under steady-state conditions and upon injection of MAM into the forepaw. Under steady-state conditions, the two strains showed differences in the dendritic cell (DC) subset composition. When MAM was injected, the number of T cells in LEW.BN-4-10 rats producing T(h)2 cytokines such as IL-4 and IL-13 was significantly increased compared with LEW. The data suggest that these differences in the microenvironments in LN of LEW and LEW.BN-4-10 rats resulted in different susceptibility to the disease (increase of cells in LN and paw swelling). In addition, deviations in the distribution and function of injected effector T cells were found in the LN of LEW and LEW.BN-4-10 rats after MAM treatment. The data indicate that the IL-6 and IL-4 gene clusters are involved in polarizing T cell responses in vivo.     

Clonal lineage tracing reveals shared origin of conventional and plasmacytoid dendritic cells

1. Download : Download high-res image (131KB)
2. Download : Download full-size image