Dendritic cells revisited in human allergic rhinitis and asthma

The role of dendritic cells (DCs) in airway allergy has been studied for 15 years; recent data has highlighted the cross talk with airway epithelial cells and environmental factors (allergens, virus) during the inception and exacerbation of allergic asthma. Although murine models have provided key information, it remains uncertain to what extent these basic mechanisms take place in human allergic disease, notably with regard to different clinical phenotypes. In the present review, we discuss new evidence regarding mechanisms of DC regulation in the mouse which could be important in human asthma. Finally, after discussing the effects of current therapies on DC biology, we focus on pathways that could represent targets for future therapies.     

Functional expression of granzyme B in human plasmacytoid dendritic cells: a role in allergic inflammation

Background Plasmacytoid dendritic cells (pDCs) are involved in a variety of immune functions. However, the expression of cytotoxic granule proteins like granzymes and perforin in human pDCs is still poorly understood. Objective The aim of this study was to systematically analyse the expression and regulation of cytotoxic granule proteins in human pDCs. Methods The expression of cytotoxic proteins was analysed by RT‐PCR, flow cytometry, and fluorescence microscopy. The functional expression of these proteins was confirmed in a flow‐cytometry‐based cytotoxicity assay using K562 cells as targets. In order to analyse the regulation of pDC‐derived cytotoxic proteins in infectious and allergic diseases, human pDCs were analysed after stimulation with toll‐like receptor (TLR)7/9 ligands and in the human asthma model of segmental allergen challenge. Results Granzyme B (GrB), but not the granzymes A, H, K, M or perforin, was specifically expressed by human pDCs and this GrB expression was up‐regulated by IL‐3 stimulation. In addition, IL‐3‐stimulated pDCs were found to kill K562 cells in a GrB‐ and caspase‐dependent manner. TLR7/9 ligands significantly suppressed GrB expression in pDCs. In contrast, there was an up‐regulation of GrB in endobronchial pDCs 24 h after allergen challenge, and this was accompanied by enhanced GrB concentrations in bronchoalveolar lavage fluid. Conclusion We report the selective expression of GrB in human pDCs and show for the first time pDC‐mediated GrB‐ and caspase‐dependent cytotoxicity against target cells. In addition, the regulation of GrB expression was investigated in vitro and in vivo providing an evidence for a specific role of pDC‐derived GrB in allergic inflammation. Cite this as: K. Bratke, J. Nielsen, F. Manig, C. Klein, M. Kuepper, S. Geyer, P. Julius, M. Lommatzsch and J. C. Virchow, Clinical & Experimental Allergy, 2010 (40) 1015–1024.     

Possible role of macrophages in allergic rhinitis

Mononuclear phagocytes have been investigated in biopsies taken from the nasal mucosa and in epithelial cell samples from 22 grass-pollen-allergic subjects before season, after allergen challenge and during season by means of immunohistochemistry and electron microscopy. The cells were positive for CD68/EBM11 and HLA-DR, but failed to react with CD1 and CD23/BB10. The cells increased in number during season as well as after allergen challenge, especially in the upper part of the mucosa. Heteromorphy of macrophages, as seen by transmission electron microscopy, confirmed the presence of diverse macrophage subpopulations in the nasal mucosa of allergic subjects. Using brush sampling techniques, CD68-positive and HLA-DR-positive cells significantly increased in epithelial cell samples 4-8 h after allergen challenge, indicating a central role of these cells not only in antigen processing but also in late phase reactions of allergic rhinitis.     

An electron microscopic study of migrating cells in the nasal epithelial compartment of human allergic rhinitis

Since intraepithelial migrating cells are the first to come into contact with various foreign particles inhaled and deposited on the nasal surface, it is important to study the distribution and function of these cells in the epithelial layer of nasal mucosa. We examined nasal scrapings by means of electron microscopy and electron microscope immunocytochemistry and found that lymphocytes were the major population in the epithelial layer, followed by eosinophils, basophilic cells, globule leukocytes and neutrophils in the order of predominance in patients with allergic rhinitis. However, no significant difference was noted in lymphocyte population between the allergy group and the chronic infectious rhinitis group, while significant increase was found in the normal group than in other two groups. Meanwhile, significant difference of eosinophils and basophilic cells were found between allergic group and non-allergic group. Globule leucocytes, characterized by their huge and irregular size and granules, were observed in the allergy group and the implication of their existence was discussed. In immunoelectron microscopic study, CD8 positive cells were more numerous than CD4 positive cells. However there was no relation between the surface marker and ultrafine structure.     

Therapeutic potential of IFN-gamma-modified dendritic cells in acute and chronic experimental allergic encephalomyelitis

Dendritic cells (DC) are antigen-presenting cells specialized to regulate immune responses. DC not only control immunity, but also maintain tolerance to self-antigens-two complementary functions that would ensure the integrity of the organism in an environment full of pathogens. Here we report that splenic DC that had been exposed in vitro to IFN-gamma (IFN-gamma-DC) exhibit therapeutic potential on acute experimental allergic encephalomyelitis (EAE) in Lewis rats, and on chronic-relapsing EAE in B6 and SJL/J mice. During incipient EAE [day 5 post-immunization (p.i.) in rats, day 7 p.i. in mice], IFN-gamma-DC were injected s.c. Severity of clinical signs of EAE was dramatically inhibited in animals injected with IFN-gamma-DC, showing normal magnetic resonance imaging (MRI) of the spinal cord and brain. In contrast, the EAE rats receiving PBS or naive DC had severe clinical signs with multiple and extensive MRI lesions in the spinal cord and brain. IFN-gamma-DC triggered an antigen-specific IFN-gamma production, and induced apoptosis of CD4(+) T cells possibly through DC expressing indoleamine 2,3-dioxygenase and/or an IFN-gamma-dependent pathway. As a result, infiltration of macrophages and CD4(+) T cells within the spinal cords was dramatically reduced in animals injected with IFN-gamma-DC as compared to animals injected with PBS or naive DC. This approach may represent a novel possibility of individualized immunotherapy using autologous, in vitro modified DC as a complement to conventional therapy in multiple sclerosis and other diseases with an autoimmune background.     

CD8alpha dendritic cells and immune protection from experimental allergic encephalomyelitis

Dendritic cells (DC) represent a phenotypically heterogeneous population endowed with two important biological functions, immunity and tolerance. Here we report that the injection of splenic CD8alpha(+) DC, derived from rats with experimental allergic encephalomyelitis (EAE), delayed the onset and suppressed the severity of EAE in Lewis rats. This was accompanied by the lack of magnetic resonance imaging (MRI) lesions in the brain and spinal cord and by reduced numbers of inflammatory cells within the central nervous system. Injection of CD8(alpha+) DC inhibited T cell proliferation that may relate to increased interferon (IFN)-gamma and nitric oxide production. Although CD8(+)CD28(-) suppressor T cells, apoptotic cells and co-stimulatory molecules were not altered, CD4(+) T cells expressing interleukin (IL)-10 were augmented in rats receiving CD8alpha(+) DC compared to rats receiving total DC or medium. These results demonstrate that rat splenic CD8alpha(+) DC could provide a cellular basis for a novel, individualized immunotherapy using autologous DC as a complement to conventional therapy in diseases with an autoimmune background such as multiple sclerosis.     

The role of leukotrienes in allergic rhinitis.

OBJECTIVE: To review the role of cysteinyl leukotrienes (cysLTs) in allergic rhinitis and the scientific rationale for therapy with leukotriene receptor antagonists (LTRAs). DATA SOURCES: Relevant basic science and clinical articles were identified by a search of the PubMed database for articles published from 1984 to 2004 using the following keywords: allergic rhinitis; nose; immune response; allergen challenge; leukotrienes C, D, and E; cysteinyl leukotriene; cysteinyl leukotriene receptor; cytokine; leukocyte; montelukast; zafirlukast; and pranlukast. STUDY SELECTION: The authors' expert opinion was used to select studies for inclusion in this review. RESULTS: CysLTs are synthesized via 5-lipoxygenase metabolism of arachidonic acid by mast cells and basophils during the early-phase response to antigen and by eosinophils and macrophages during the late phase. The cysLT levels in nasal secretions are elevated after short-term allergen instillation and in allergy season in patients with allergic rhinitis. These lipid mediators act locally and systemically by interacting with receptors, particularly the cysLT1 receptor, on target cells. Evidence derived from topical application of cysLTs in the nose and from the effects of LTRAs indicates that cysLTs contribute to nasal mucous secretion, congestion, and inflammation. CysLTs promote allergic inflammation by enhancing immune responses and the production, adhesion, migration, and survival of inflammatory cells such as eosinophils. They also increase the generation of an array of other proinflammatory mediators, such as cytokines, which in turn increase the production of and receptors for cysLTs. Clinical trials have demonstrated that LTRAs have significant but modest efficacy as single agents but additive efficacy when used with other classes of agents. CONCLUSIONS: CysLTs fulfill the criteria for relevant mediators of allergic rhinitis via their diverse effects on immune, inflammatory, and local structural components of disease. By blocking the cysLT1 receptor responsible for most of these effects, LTRAs represent a useful approach to treatment of this important and prevalent disorder.     

Cutaneous dendritic cells in allergic inflammation

The skin represents a physical barrier, which is capable of protecting the body from damaging invaders. Moreover, the skin operates as an active immunological organ, harbouring a complex network of dendritic cells (DCs), which serve as a bridge between innate and adaptive immunity. Equipped with specific pattern recognition receptors (PRRs), DCs are able to capture, process and present antigens to naïve T cells in the skin draining lymph nodes, thereby inducing adaptive antigen‐specific immunity. However, the outcome of the immune response is shaped by numerous factors including the DC subtype, maturation state of DCs, composition of PRRs expressed by DCs, type of pathogen as well as factors in the microenvironment. Thus, cutaneous DC subtypes are known to contribute to both, peripheral tolerance and the generation of allergic skin inflammation. Identifying the underlying mechanisms is a challenging task in understanding DC biology. Based on their functional diversity, cutaneous DCs might represent promising therapeutic targets, with the potential of down‐modulating pro‐inflammatory immune responses and inducing tolerogenic pathways, thereby ensuring the maintenance of tissue homeostasis and restoring the balance of dysregulated immune reactions in the context of allergic skin diseases. In this review, we summarize the versatile character of DC subtypes in human skin and highlight their phenotypic characteristics and role in allergic skin inflammation. In addition, we discuss current therapeutic approaches for the management of inflammatory skin diseases such as atopic dermatitis with the main focus on strategies targeting DCs. We point towards potential challenges, benefits, risks and limitations for the treatment of patients.     

AIRE is not essential for the induction of human tolerogenic dendritic cells

Loss-of-function mutations of the Autoimmune Regulator (AIRE) gene results in organ-specific autoimmunity and disease Autoimmune Polyendocrinopathy type 1 (APS1)/Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy (APECED). The AIRE protein is crucial in the induction of central tolerance, promoting ectopic expression of tissue-specific antigens in medullary thymic epithelial cells and enabling removal of self-reactive T-cells. AIRE expression has recently been detected in myeloid dendritic cells (DC), suggesting AIRE may have a significant role in peripheral tolerance. DC stimulation of T-cells is critical in determining the initiation or lack of an immune response, depending on the pattern of costimulation and cytokine production by DCs, defining immunogenic/inflammatory (inflDC) and tolerogenic (tolDC) DC. In AIRE-deficient patients and healthy controls, we validated the role of AIRE in the generation and function of monocyte-derived inflDC and tolDCs by determining mRNA and protein expression of AIRE and comparing activation markers (HLA-DR/DP/DQ,CD83,CD86,CD274(PDL-1),TLR-2), cytokine production (IL-12p70,IL-10,IL-6,TNF-α,IFN-γ) and T-cell stimulatory capacity (mixed lymphocyte reaction) of AIRE+ and AIRE- DCs. We show for the first time that: (1) tolDCs from healthy individuals express AIRE; (2) AIRE expression is not significantly higher in tolDC compared to inflDC; (3) tolDC can be generated from APECED patient monocytes and (4) tolDCs lacking AIRE retain the same phenotype and reduced T-cell stimulatory function. Our findings suggest that AIRE does not have a role in the induction and function of monocyte-derived tolerogenic DC in humans, but these findings do not exclude a role for AIRE in peripheral tolerance mediated by other cell types.