Flt3 ligand generates morphologically distinct semimature dendritic cells in ovalbumin-sensitized mice

Fms-like tyrosine kinase 3 ligand-dependent dendritic cells in autoimmune inflammation

Dendritic cells (DCs) are specialized in capture, processing and presentation of antigens to T cells. Depending on the type of DC and its activation state, the interaction of DCs with naive T cells can lead to different types of immune response, or to T-cell tolerance. The existence of many specialized subtypes of DCs with particular functions has raised the need to distinguish DCs formed in steady-state from those produced during an inflammatory response. In patients with autoimmune disease and in experimental animal models of autoimmunity, DCs show abnormalities in both numbers and activation state, expressing immunogenic levels of co-stimulatory molecules and pro-inflammatory cytokines. Initial in vitro studies of cytokines in DC development revealed distinct and important roles for the receptor tyrosine kinases, granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF, also called CSF1) and fms-like tyrosine kinase 3 ligand (Flt3L) in the generation of DCs. Flt3L is critical for instructing DC generation throughout different organs and regulates DC development from Flt3(+) lymphoid and myeloid-committed progenitors to DCs in vivo. The aim of this review is to provide an overview of the role of Flt3L-dependent DCs in the immunopathogenesis of autoimmunity and chronic inflammation and its potential as therapeutic targets.

Mitochondrial Dysfunction and Oxidative Stress in Asthma: Implications for Mitochondria-Targeted Antioxidant Therapeutics

Asthma is a complex, inflammatory disorder characterized by airflow obstruction of variable degrees, bronchial hyper-responsiveness, and airway inflammation. Asthma is caused by environmental factors and a combination of genetic and environmental stimuli. Genetic studies have revealed that multiple loci are involved in the etiology of asthma. Recent cellular, molecular, and animal-model studies have revealed several cellular events that are involved in the progression of asthma, including: increased Th2 cytokines leading to the recruitment of inflammatory cells to the airway, and an increase in the production of reactive oxygen species and mitochondrial dysfunction in the activated inflammatory cells, leading to tissue injury in the bronchial epithelium. Further, aging and animal model studies have revealed that mitochondrial dysfunction and oxidative stress are involved and play a large role in asthma. Recent studies using experimental allergic asthmatic mouse models and peripheral cells and tissues from asthmatic humans have revealed antioxidants as promising treatments for people with asthma. This article summarizes the latest research findings on the involvement of inflammatory changes, and mitochondrial dysfunction/oxidative stress in the development and progression of asthma. This article also addresses the relationship between aging and age-related immunity in triggering asthma, the antioxidant therapeutic strategies in treating people with asthma.

Pathogenesis of allergic airway inflammation

Advances have been made in defining the mechanisms for the control of allergic airway inflammation in response to inhaled antigens. Several genes, including ADAM33, DPP10, PHF11, GPRA, TIM-1, PDE4D, OPN3, and ORMDL3, have been implicated in the pathogenesis and susceptibility to atopy and asthma. Growing evidence associates asthma with a systemic propensity for allergic T-helper type 2 cytokines. Disordered coagulation and fibrinolysis also exacerbate asthma symptoms. Balance among functionally distinct dendritic cell subsets contributes to the outcome of T-cell-mediated immunity. Allergen-specific T-regulatory cells play a pivotal role in the development of tolerance to allergens and immune suppression. The major emphasis on immunotherapy for asthma during the past decade has been to direct the immune response to a type 1 response, or immune tolerance. In this review, we discuss the current information on the pathogenesis of allergic airway inflammation and potential immunotherapy, which could be beneficial in the treatment of airway inflammation, allergy, and asthma.

Fms-like tyrosine kinase 3 ligand regulates migratory pattern and antigen uptake of lung dendritic cell subsets in a murine model of allergic airway inflammation

Fms-like tyrosine kinase 3 ligand (Flt3L) reverses the features of allergic airway inflammation and increases a Th2-suppressive regulatory lung CD11c(high)CD11b(low) dendritic cell (DC) subset in a mouse model. We examined the migratory pattern and Ag uptake efficiency of lung DC subsets in the therapeutic effect of Flt3L. Lung CD11c(high)CD11b(low) and CD11c(low)CD11b(high) DCs from PBS-treated, OVA-sensitized, and Flt3L-treated/OVA-sensitized BALB/c mice were sorted using MACS and FACS for phenotype analysis. Lymphatic chemokine expression in thoracic lymph nodes was determined by immunohistochemistry. Migration of two lung DC subsets to lymphatic chemokines was examined in vitro using a Transwell chemotaxis assay. Labeled Ag was intranasally delivered into mouse lung to track the migration and Ag uptake of lung DCs. The in vitro cytokine secretion of mediastinal lymph node cells was determined using ELISA. CD11c(low)CD11b(high) DCs have higher expression of CCR5, CCR6, and CCR7, but lower expression of CCR2 than CD11c(high)CD11b(low) DCs. CD11c(low)CD11b(high) DCs in Flt3L-treated/OVA-sensitized mice demonstrated a less mature phenotype, inefficiency in Ag uptake, and impaired migration in vitro to lymphatic chemokine than those in OVA-sensitized mice. Administration of Flt3L decreased the expression of CCR5 and CCR7 in CD11c(low)CD11b(high) DCs in OVA-sensitized mice. Fewer Ag-carrying cells were detected in the lungs and lymph nodes in Flt3L-treated/OVA-sensitized mice than OVA-sensitized mice with a greater decrease in CD11c(low)CD11b(high) DCs. Mediastinal lymph node cells from Flt3L-treated mice secreted higher levels of Th1 cytokines and IL-10 than OVA-sensitized mice in vitro. In conclusion, Flt3L-generated lung immunogenic CD11c(low)CD11b(high) DCs have a less mature phenotype, impaired Ag uptake, and impaired migration to draining lymph nodes.

Coxsackievirus B3 infection promotes generation of myeloid dendritic cells from bone marrow and accumulation in the myocardium

Myocarditis is associated with increased number of CD4+ T cells in the myocardium after coxsackievirus B3 (CVB3) infection. Previous studies show that CD11c+ myeloid dendritic cells (mDC) loaded with myosin could induce myocarditis. This study aims to investigate the generation and accumulation of mDC in CVB3-induced myocarditis. The presence of mDC in myocardium was detected by immunohistochemisty. Bone marrow-derived mDC were generated from uninfected and CVB3-infected mice. The percentage of CD11c+ mDC on cultured cells and mean fluorescence index (MFI) of double positive cells (CD11c+CD40+, CD11c+CD80+) were measured by flow cytometry. The expression of chemokine receptors (CCR5, CCR7) on mDC and chemokines (CCL4, CCL19) in the myocardium was detected. The migration of mDC in response to CCL4 or CCL19 was measured by chemotaxis assay. Mature mDC were elevated in the myocardium from CVB3-infected mice. The percentage of mDC generated from CVB3-infected group was increased. The MFI of CD11c+CD40+ and CD11c+CD80+ was increased in CVB3-infected group. The mDC showed a down-regulation of CCR5 and unaffected CCR7 mRAN levels associated with elevated CCL4 and CCL19 in the myocardium in CVB3-infected group. Numbers of migrating bone marrow-derived mDC from CVB3-infected mice were increased in vitro. We conclude that CVB3 infection induced the greater generation of mDC from bone marrow and accumulation of mature mDC in myocardial tissues. This migration was associated with increased levels of both CCL4 and CCL19 in the heart tissue. These suggest that blocking the migration of mDC may provide a novel therapy for myocarditis.

Fms-like tyrosine kinase 3 ligand increases a lung DC subset with regulatory properties in allergic airway inflammation

BACKGROUND

Dendritic cell (DC) subsets display different functional roles in regulating immune responses and lead to various outcomes, including T(H)1 versus T(H)2 or regulatory versus immunologic responses. Administration of Fms-like tyrosine kinase 3 (Flt3) ligand prevents and reverses allergic airway inflammation and airway hyperresponsiveness in a mouse model. However, the underlying mechanisms are unclear.

OBJECTIVE

We characterized and examined the role of lung DC subsets in the therapeutic effect of Flt3 ligand.

METHODS

DCs were isolated from the lungs of ovalbumin (OVA)-sensitized and OVA-challenged mice treated with recombinant human Flt3 ligand. Two populations of CD11c+ cells labeled with fluorochrome-conjugated antibodies were sorted. The ability of the purified cells to stimulate T-cell proliferation and cytokine secretion patterns by different DC subsets was examined. Also, DCs were adoptively transferred in mice to examine their effect on pulmonary function.

RESULTS

Two DC populations, CD11c(high)CD11b(low) and CD11c(low)CD11b(high), were identified in the lungs of naive and OVA-sensitized and OVA-challenged mice with and without treatment with Flt3 ligand. The expression levels of CD8alpha, B220, CD19, F4/80, MHC II, CCR7, CD40, programmed death ligand 1, programmed death ligand 2, CD80, and CD86 were distinctly different between the 2 DC populations, which supports the notion that CD11c(high)CD11b(low) and CD11c(low)CD11b(high) DCs potentially have regulatory and immunogenic properties, respectively. Administration of Flt3 ligand increased the DCs with regulatory potential in the lungs of antigen-sensitized mice, and CD11c(high)CD11b(low) DCs acquired a maximum degree of regulatory capacity after Flt3 ligand treatment.

CONCLUSION

These data suggest that Flt3 ligand reverses airway hyperresponsiveness by regulating the function of lung DCs in a mouse model of allergic airway inflammation.

Dendritic cells in allergic airway inflammation

Dendritic cells (DCs) are primary antigen-presenting cells involved in interactions with T cells leading to the proliferation of TH1 or TH2 cell types. In asthma, predominance of TH2 cells appears to be responsible for disease pathogenesis. Differentiation of TH2 cells is driven by a variety of factors such as the expression of high levels of costimulatory molecules, the cytokine profile, and the subset of DCs. Many inflammatory cells involved in the pathogenesis of asthma either directly or indirectly modulate DC function. Traditional treatments for asthma decrease the number of airway DCs in animals as well as in patients with asthma. Immunomodulators including interleukin (IL)-10, transforming growth factor (TGF)-beta, cytosine-phosphate-guanosine-containing oligodeoxynucleotides (CpG-ODN), 1alpha,25-dihydroxyvitamin D3, and fetal liver tyrosine kinase 3 ligand (Flt3L) are involved in the modulation of the function of DCs. Based on the critical review of the interaction between DCs and other inflammatory cells, we propose that activation of T cells by DCs and sensitization to inhaled allergen and resulting airway inflammation are dependent on plasmacytoid and myeloid subset of lung DCs to induce an immune response or tolerance and are tightly regulated by T-regulatory cells. Effects of various therapeutic agents to modulate the function of lung myeloid DCs have been discussed.