Dexamethasone preferentially suppresses plasmacytoid dendritic cell differentiation and enhances their apoptotic death

Corticosteroid-depending effects on peripheral immune cell subsets vary according to disease modifying strategies in multiple sclerosis

Background

The primary treatment for acute relapses in multiple sclerosis (MS) is the intravenous administration of high-dose methylprednisolone (IVMP). However, the mechanisms through which corticosteroid treatment impacts acute neuroinflammation in people with MS (pwMS) remain not fully understood. In particular, the changes induced by glucocorticoids (GCs) on cells of the innate immune system and the differences between patients with distinct immunotherapies have received little attention to date.

Methods

We conducted immunophenotyping using flow cytometry on peripheral blood mononuclear cells of pwMS who received IVMP treatment during a relapse. We compared the impact of an IVMP treatment on a broad variety of immune cell subsets within three groups: twelve patients who were treatment-naïve to disease modifying therapies (wDMT) to ten patients on platform therapies (PT) and eighteen patients on fingolimod therapy (FTY).

Results

We observed pronounced interindividual short- and intermediate-term effects of IVMP on distinct immune cells subsets. In addition to the well-documented decrease in T-helper cells (Th cells), we detected significant alterations after the first IVMP infusion within the innate immune response among neutrophil, eosinophil and basophil granulocytes, monocytes and plasmacytoid dendritic cells (pDCs). When comparing patients wDMT to the PT and FTY cohorts, we found that IVMP had a similar impact on innate immune cells across all treatment groups. However, we did not observe a significant further decline in T lymphocyte counts during IVMP in patients with pre-existing lymphopenia under FTY treatment. Although T cell apoptosis is considered the main mechanism of action of GCs, patients with FTY still reported symptom improvement following IVMP treatment.

Conclusion

In addition to T cell suppression, our data suggests that further immunoregulatory mechanisms of GC, particularly on cells of the innate immune response, are of greater significance than previously understood. Due to the regulation of the adaptive immune cells by DMTs, the impact of GC on these cells varies depending on the underlying DMT. Additional studies involving larger cohorts and cerebrospinal fluid samples are necessary to gain a deeper understanding of the immune response to GC in pwMS with different DMTs during relapse to define and explain differences in clinical response profiles.

SARS-CoV-2 induces human plasmacytoid predendritic cell diversification via UNC93B and IRAK4

Several studies have analyzed antiviral immune pathways in late-stage severe COVID-19. However, the initial steps of SARS-CoV-2 antiviral immunity are poorly understood. Here we have isolated primary SARS-CoV-2 viral strains and studied their interaction with human plasmacytoid predendritic cells (pDCs), a key player in antiviral immunity. We show that pDCs are not productively infected by SARS-CoV-2. However, they efficiently diversified into activated P1-, P2-, and P3-pDC effector subsets in response to viral stimulation. They expressed CD80, CD86, CCR7, and OX40 ligand at levels similar to influenza virus-induced activation. They rapidly produced high levels of interferon-α, interferon-λ1, IL-6, IP-10, and IL-8. All major aspects of SARS-CoV-2-induced pDC activation were inhibited by hydroxychloroquine. Mechanistically, SARS-CoV-2-induced pDC activation critically depended on IRAK4 and UNC93B1, as established using pDC from genetically deficient patients. Overall, our data indicate that human pDC are efficiently activated by SARS-CoV-2 particles and may thus contribute to type I IFN-dependent immunity against SARS-CoV-2 infection.

SARS-CoV-2 induces human plasmacytoid pre-dendritic cell diversification via UNC93B and IRAK4

Several studies have analyzed antiviral immune pathways in late-stage severe COVID-19. However, the initial steps of SARS-CoV-2 antiviral immunity are poorly understood. Here, we have isolated primary SARS-CoV-2 viral strains, and studied their interaction with human plasmacytoid pre-dendritic cells (pDC), a key player in antiviral immunity. We show that pDC are not productively infected by SARS-CoV-2. However, they efficiently diversified into activated P1-, P2-, and P3-pDC effector subsets in response to viral stimulation. They expressed CD80, CD86, CCR7, and OX40 ligand at levels similar to influenza virus-induced activation. They rapidly produced high levels of interferon-α, interferon-λ1, IL-6, IP-10, and IL-8. All major aspects of SARS-CoV-2-induced pDC activation were inhibited by hydroxychloroquine. Mechanistically, SARS-CoV-2-induced pDC activation critically depended on IRAK4 and UNC93B1, as established using pDC from genetically deficient patients. Overall, our data indicate that human pDC are efficiently activated by SARS-CoV-2 particles and may thus contribute to type I IFN-dependent immunity against SARS-CoV-2 infection.

Epidemiologic and clinical characteristics of heart transplant recipients during the 2019 coronavirus outbreak in Wuhan, China: A descriptive survey report

BACKGROUND

The epidemiologic and clinical characteristics of heart transplant (HTx) recipients during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic remains unclear. We studied the characteristics of HTx recipients from December 20, 2019, to February 25, 2020, in an effort to understand their risk and outcomes.

METHODS

All accessible HTx recipients were included in this single-center retrospective study. We collected information on the recipients using a web-based questionnaire as well as the hospital database.

RESULTS

We followed 87 HTx recipients (72.4% were men, and the average age was 51 years). A total of 79 recipients resided in Hubei, and 57 recipients had a Wuhan-related history of travel or contact. Most took precautionary measures while in contact with suspicious crowds, and 96.6% of the families and communities undertook prevention and quarantine procedures. Four upper airway infections were reported, and 3 of them tested negative for SARS-CoV-2 (the fourth recovered and was not tested). All cases were mild and successfully recovered after proper treatment. Laboratory results of 47 HTx cases within the last 2 months were extracted. Of these, 21.3% of recipients had pre-existing lymphopenia, and 87.2% of recipients had a therapeutic concentration of tacrolimus (5-12 ng/ml). Liver and kidney insufficiency was seen in 5 and 6 recipients, respectively.

CONCLUSION

HTx recipients who practiced appropriate prevention measures had a low rate of infection with SARS-CoV-2 and transition to the associated disease COVID-19. These early data will require confirmation as the pandemic establishes around the world.

Cigarette Smoke Decreases the Maturation of Lung Myeloid Dendritic Cells

BACKGROUND

Conflicting data exist on the role of pulmonary dendritic cells (DCs) and their maturation in patients with chronic obstructive pulmonary disease (COPD). Herein, we investigated whether disease severity and smoking status could affect the distribution and maturation of DCs in lung tissues of patients undergoing elective pneumectomy or lobectomy for suspected primary lung cancer.

MATERIALS AND METHODS

A total of 75 consecutive patients were included. Spirometry testing was used to identify COPD. Lung parenchyma sections anatomically distant from the primary lesion were examined. We used flow cytometry to identify different DCs subtypes-including BDCA1-positive myeloid DCs (mDCs), BDCA3-positive mDCs, and plasmacytoid DCs (pDCs)-and determine their maturation markers (CD40, CD80, CD83, and CD86) in all participants. We also identified follicular DCs (fDCs), Langerhans DCs (LDCs), and pDCs in 42 patients by immunohistochemistry.

RESULTS

COPD was diagnosed in 43 patients (16 current smokers and 27 former smokers), whereas the remaining 32 subjects were classified as non-COPD (11 current smokers, 13 former smokers, and 8 never smokers). The number and maturation of DCs did not differ significantly between COPD and non-COPD patients. However, the results of flow cytometry indicated that maturation markers CD40 and CD83 of BDCA1-positive mDCs were significantly decreased in smokers than in non-smokers (P = 0.023 and 0.013, respectively). Immunohistochemistry also revealed a lower number of LDCs in COPD patients than in non-COPD subjects.

CONCLUSIONS

Cigarette smoke, rather than airflow limitation, is the main determinant of impaired DCs maturation in the lung.

Plasmacytoid dendritic cells in allogeneic hematopoietic cell transplantation: benefit or burden?

Plasmacytoid dendritic cells (pDCs) bridge innate and adaptive immune responses and have important roles in hematopoietic engraftment, GvHD and graft-versus-leukemia responses following allogeneic hematopoietic cell transplantation (HCT). In addition, pDCs mediate antiviral immunity, particularly as they are the body's primary cellular source of type I interferon. Given their pleiotropic roles, pDCs have emerged as cells that critically impact transplant outcomes, including overall survival. In this article, we will review the pre-clinical and clinical literature, supporting the crucial roles that pDCs assume as key immune effector cells during HCT.

Accumulation and therapeutic modulation of 6-sulfo LacNAc(+) dendritic cells in multiple sclerosis

Objective:

To examine the potential role of 6-sulfo LacNAc⁺ (slan) dendritic cells (DCs) displaying pronounced proinflammatory properties in the pathogenesis of multiple sclerosis (MS).

Methods:

We determined the presence of slanDCs in demyelinated brain lesions and CSF samples of patients with MS. In addition, we explored the impact of methylprednisolone, interferon-β, glatiramer acetate, or natalizumab on the frequency of blood-circulating slanDCs in patients with MS. We also evaluated whether interferon-β modulates important proinflammatory capabilities of slanDCs.

Results:

SlanDCs accumulate in highly inflammatory brain lesions and are present in the majority of CSF samples of patients with MS. Short-term methylprednisolone administration reduces the percentage of slanDCs in blood of patients with MS and the proportion of tumor necrosis factor-α– or CD150-expressing slanDCs. Long-term interferon-β treatment decreases the percentage of blood-circulating slanDCs in contrast to glatiramer acetate or natalizumab. Furthermore, interferon-β inhibits the secretion of proinflammatory cytokines by slanDCs and their capacity to promote proliferation and differentiation of T cells.

Conclusion:

Accumulation of slanDCs in highly inflammatory brain lesions and their presence in CSF indicate that slanDCs may play an important role in the immunopathogenesis of MS. The reduction of blood-circulating slanDCs and the inhibition of their proinflammatory properties by methylprednisolone and interferon-β may contribute to the therapeutic efficiency of these drugs in patients with MS.

Stressful presentations: mild cold stress in laboratory mice influences phenotype of dendritic cells in naïve and tumor-bearing mice

The ability of dendritic cells (DCs) to stimulate and regulate T cells is critical to effective anti-tumor immunity. Therefore, it is important to fully recognize any inherent factors which may influence DC function under experimental conditions, especially in laboratory mice since they are used so heavily to model immune responses. The goals of this report are to 1) briefly summarize previous work revealing how DCs respond to various forms of physiological stress and 2) to present new data highlighting the potential for chronic mild cold stress inherent to mice housed at the required standard ambient temperatures to influence baseline DCs properties in naïve and tumor-bearing mice. As recent data from our group shows that CD8⁺ T cell function is significantly altered by chronic mild cold stress and since DC function is crucial for CD8⁺ T cell activation, we wondered whether housing temperature may also be influencing DC function. Here we report that there are several significant phenotypical and functional differences among DC subsets in naïve and tumor-bearing mice housed at either standard housing temperature or at a thermoneutral ambient temperature, which significantly reduces the extent of cold stress. The new data presented here strongly suggests that, by itself, the housing temperature of mice can affect fundamental properties and functions of DCs. Therefore differences in basal levels of stress due to housing should be taken into consideration when interpreting experiments designed to evaluate the impact of additional variables, including other stressors on DC function.

Fluticasone impact on airway dendritic cells in smokers: a randomized controlled trial

Background

Myeloid Dendritic cells are key drivers of inflammation in smoke-related lung diseases, whereas plasmacytoid DCs play a crucial role in the defense against infections. Effects of inhaled corticosteroids (ICS) on airway DCs in smokers are unknown.

Methods

In this randomized, double-blind, placebo-controlled clinical trial, 45 active cigarette smokers inhaled placebo, fluticasone or fluticasone plus salmeterol twice daily for 4 weeks. Bronchoalveolar lavage fluid DCs were analyzed using four-color flow cytometry before and after the inhalation period. In addition, fluticasone effects were tested on T-cell proliferation in co-cultures with blood myeloid DCs from smokers.

Results

Inhalation of fluticasone plus salmeterol, but not fluticasone alone or placebo, reduced endobronchial concentrations of myeloid DCs (median decrease: 24%), macrophages (median decrease: 26%) and neutrophils (median decrease: 76%). In contrast, fluticasone reduced plasmacytoid DC concentrations independently of salmeterol. There were no changes in the expression of function-associated surface molecules on myeloid DC (such as CD1a, Langerin, BDCA-1, CD83 or CCR5) in all groups after treatment. Fluticasone (either alone or in combination with salmeterol) suppressed T-cell proliferation in co-cultures with blood myeloid DCs from smokers.

Conclusions

Resistance to ICS monotherapy in smokers might in part be due to lacking effects on airway myeloid DCs, whereas the increased risk for infections during ICS therapy could be attributable to a reduction in plasmacytoid DCs. Combination therapy of fluticasone with salmeterol is associated with a reduction in airway myeloid DCs, but also airway macrophages and neutrophils.

Trial registration

Registered at ClinicalTrials.gov (identifier: NCT00908362) and the European Clinical Trial Database, EudraCT (identifier: 2009-009459-40).

Dendritic cell-based approaches for therapeutic immune regulation in solid-organ transplantation

To avoid immune rejection, allograft recipients require drug-based immunosuppression, which has significant toxicity. An emerging approach is adoptive transfer of immunoregulatory cells. While mature dendritic cells (DCs) present donor antigen to the immune system, triggering rejection, regulatory DCs interact with regulatory T cells to promote immune tolerance. Intravenous injection of immature DCs of either donor or host origin at the time of transplantation have prolonged allograft survival in solid-organ transplant models. DCs can be treated with pharmacological agents before injection, which may attenuate their maturation in vivo. Recent data suggest that injected immunosuppressive DCs may inhibit allograft rejection, not by themselves, but through conventional DCs of the host. Genetically engineered DCs have also been tested. Two clinical trials in type-1 diabetes and rheumatoid arthritis have been carried out, and other trials, including one trial in kidney transplantation, are in progress or are imminent.

Nuclear receptor expression patterns in murine plasmacytoid and conventional dendritic cells

Dendritic cells (DC) play a central role in the immune system. They can either induce immunity or promote tolerance. The DC family is generally comprised of two functionally distinct DC subsets. Conventional dendritic cells (cDC) are the classical antigen presenting cells; plasmacytoid dendritic cells (pDC) are the main producers of type I interferons thereby serving innate immunity. Upon activation DCs are able to present antigen and stimulate T cells. The immune modulatory functions of DCs largely depend on the recognition of soluble cues. Besides pathogen derived cues, recent data indicate that the tissue micro-environment, i.e. of the gut and skin affects cDC function. Many of these micro-environmental factors are ligands for the nuclear receptor (NR) family of transcription regulators known to affect immunity and tolerance. Whether pDC function is also influenced by tissue derived cues, like hormones, vitamins and metabolic products, is largely unknown. Here, we investigated the NR expression profile of murine pDCs and cDCs. We assessed the mRNA levels of 19 NRs of in vitro derived as well as ex vivo isolated DCs from four different lymphoid tissues. We observed that cDCs and pDCs expressed the same repertoire of NRs. Expression levels, however, differed between the two subsets, especially upon maturation of DCs. These data imply that NR ligands do impact pDC function and that their activity might be regulated in a DC-specific manner.

Reconstitution of 6-sulfo LacNAc dendritic cells after allogeneic stem-cell transplantation

BACKGROUND

Infections and acute graft-versus-host disease (GvHD) represent major complications of allogeneic stem-cell transplantation (SCT). Dendritic cells (DCs) display an extraordinary capacity to induce innate and adaptive immune responses. Therefore, they play a crucial role in the elimination of pathogens and in the pathogenesis of acute GvHD. 6-Sulfo LacNAc DCs (slanDCs) are a major subpopulation of human blood DCs with a high proinflammatory capacity. We investigated for the first time the reconstitution of slanDCs in the blood of patients after SCT and the modulation of their frequency by bacterial infection, cytomegalovirus (CMV) reactivation, and acute GvHD.

METHODS

The frequency of slanDCs, CD1c myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) in the peripheral blood was quantified by flow cytometry in 80 patients after SCT. To assess individual DC subsets, we used pregating of the HLADRLin subset and antibodies against slanDCs, blood DC antigen 1 (CD1c mDCs), and blood DC antigen 2 (pDCs).

RESULTS

SlanDCs showed the slowest reconstitution in the first month after SCT compared with CD1c mDCs and pDCs. Interestingly, in the second and third months after SCT, their percentage steadily increased, and slanDCs were the most abundant DC subset. In addition, we observed a markedly reduced frequency of slanDCs in the blood of patients with bacterial infection, CMV reactivation, or severe acute GvHD. Furthermore, slanDCs showed the most prominent reduction after steroid treatment of acute GvHD.

CONCLUSIONS

These results indicate that SCT-associated complications such as bacterial infection, CMV reactivation, and acute GvHD can significantly modulate the frequency of slanDCs.

Preterm neonates display altered plasmacytoid dendritic cell function and morphology

Bacterial and viral infections cause high rates of morbidity and mortality in premature newborns. In the setting of viral infection, pDCs play a key role as strong producers of IFN-α upon TLR9 activation. We analyzed pDC frequency, phenotype, morphology, and function in CB of preterm and term newborns in comparison with adults. Whereas all age groups show similar pDC numbers, BDCA-2, CD123, and TLR9 levels, the expression of BDCA-4 and capacity to produce IFN-α upon TLR9 challenge were decreased significantly in preterm neonates. Furthermore, we show by means of electron microscopy that pDCs from preterm newborns exhibit a distinct, "immature" morphology. Taken together, these findings suggest decreased functionality of pDCs in the premature newborn. The reduced capacity to produce IFN-α is likely to render such infants more susceptible to viral infections.

Glucocorticoid receptor translational isoforms underlie maturational stage-specific glucocorticoid sensitivities of dendritic cells in mice and humans

Although glucocorticoids are a profoundly important class of anti-inflammatory and immunosuppressive agents, their actions in dendritic cells (DCs) are not well understood. We found that dexamethasone, a potent glucocorticoid, selectively induced apoptosis in mature, but not in immature, DCs in healthy mice, in mice with experimental airway inflammation, and in vitro in bone marrow–derived DCs. Distinct glucocorticoid receptor (GR) translational isoforms expressed in immature and mature DCs probably contribute to the DC maturational stage-specific glucocorticoid sensitivity. The GR-D isoforms were the predominant isoforms in immature DCs, whereas the proapoptotic GR-A isoform was the main isoform in mature DCs. Ectopic expression of the GR-A isoform in immature DCs increased glucocorticoid sensitivity and RU486, a selective GR antagonist, inhibited the glucocorticoid sensitivity of mature DCs. Furthermore, the distinct expression pattern of GR isoforms in immature and mature murine DCs was also observed in human monocyte–derived DCs. These studies suggest that glucocorticoids may spare immature DCs and suppress mature DCs and inflammation via differential expression of GR translational isoforms.

Autoimmune Addison disease: pathophysiology and genetic complexity

Autoimmune Addison disease is a rare autoimmune disorder with symptoms that typically develop over months or years. Following the development of serum autoantibodies to the key steroidogenic enzyme, 21-hydroxylase, patients have a period of compensated or preclinical disease, characterized by elevations in adrenocortocotropic hormone and renin, before overt, symptomatic adrenal failure develops. We propose that local failure of steroidogenesis, causing breakdown of tolerance to adrenal antigens, might be a key factor in disease progression. The etiology of autoimmune Addison disease has a strong genetic component in man, and several dog breeds are also susceptible. Allelic variants of genes encoding molecules of both the adaptive and innate immune systems have now been implicated, with a focus on the immunological synapse and downstream participants in T lymphocyte antigen-receptor signaling. With the exception of MHC alleles, which contribute to susceptibility in both human and canine Addison disease, no major or highly penetrant disease alleles have been found to date. Future research into autoimmune Addison disease, making use of genome-wide association studies and next-generation sequencing technology, will address the gaps in our understanding of the etiology of this disease.

Berberine induces dendritic cell apoptosis and has therapeutic potential for rheumatoid arthritis

OBJECTIVE

To investigate the effects of berberine on dendritic cell (DC) apoptosis and its potential as a therapeutic agent in rheumatoid arthritis (RA).

METHODS

Bone marrow (BM)-derived myeloid DCs (MDCs) and plasmacytoid DCs (PDCs) were generated by culturing BM cells with granulocyte-macrophage colony-stimulating factor/interleukin-4 or flt3L, respectively. Splenic DCs, T cells, and B cells were purified using a magnetic-activated cell sorting system. In vitro apoptosis was assessed by annexin V/propidium iodide or Hoechst 33258 staining. The in vivo effects of berberine were examined in mice with collagen-induced arthritis (CIA). Immune responses against type II collagen (CII) were determined by assaying serum antibody levels, lymphocyte proliferation, and cytokine production. The proportions of DCs and apoptosis of different immune cell subsets in spleens and lymph nodes were analyzed by flow cytometry and immunohistochemistry after subset-specific surface marker labeling and TUNEL staining.

RESULTS

Exposure of MDCs to berberine during BM cell differentiation reduced cell recovery by inducing apoptosis. Sensitivity to berberine-induced apoptosis was acquired starting on day 3 of DC differentiation, and mature DCs were more sensitive to berberine than immature DCs. Murine peritoneal macrophages, RAW 264.7 cells, and Jurkat cells were insensitive to berberine-induced apoptosis. Splenic DCs were more sensitive to berberine than T and B cells. Susceptibility of PDCs to berberine-induced apoptosis was similar to that of MDCs. In mice with CIA, berberine treatment ameliorated arthritis, suppressed CII-specific immune responses, and selectively increased the incidence of apoptosis in DCs within spleens and lymph nodes.

CONCLUSION

These findings show that berberine selectively induces apoptosis in DCs. Berberine may thus represent a novel therapeutic agent for RA.

CpG-C immunotherapeutic efficacy is jeopardized by ongoing exposure to stress: potential implications for clinical use

Bi-directional influences between stress hormones and immune responses have been repeatedly documented, however, in the clinical setting they are rarely considered when immunotherapeutic approaches are used or studied in patients. As some immunotherapeutic treatments have shown great potential in animal models but have had limited success in patients, we hypothesize that ongoing psychological and physiological stress responses in patients, which do not characterize the setting of animal studies, contribute to this discrepancy. In the current study we examined the interaction between ongoing water stress and CpG-C immunotherapy to determine whether stress that precedes immunotherapy can modulate the efficacy of CpG-C immunostimulation. C57BL/6 mice were exposed to water stress or served as controls. Two hours following the commencement of the stress protocol animals were injected with CpG-C, non-CpG, or PBS, and sacrificed 1, 4 or 12h thereafter. We found that in CpG-C-treated animals stress eliminated the elevation of plasma IL-12, and synergistically elevated corticosterone levels. Furthermore, stress markedly reduced the total number of myeloid (33D1(+)), plasmacytoid (mPDCA-1(+)) and plasmacytoid-derived (33D1(+)mPDCA-1(+)) dendritic cells in CpG-C-treated animals, as well as the numbers of these cell sub-types expressing CD11b, CD80 and CD69. These changes were more dramatic in the blood than in the spleen. Overall, these findings indicate that under no-stress conditions CpG-C induces a robust immune response, which is significantly diminished when immunostimulation is attempted during ongoing stress. If these findings hold in humans, potential prophylactic treatments should be found to limit the deleterious effects of ongoing stress on the efficacy of immunotherapy.

Plasmacytoid dendritic cells and the control of herpesvirus infections

Type-I interferons (IFN-I) are cytokines essential for vertebrate antiviral defense, including against herpesviruses. IFN-I have potent direct antiviral activities and also mediate a multiplicity of immunoregulatory functions, which can either promote or dampen antiviral adaptive immune responses. Plasmacytoid dendritic cells (pDCs) are the professional producers of IFN-I in response to many viruses, including all of the herpesviruses tested. There is strong evidence that pDCs could play a major role in the initial orchestration of both innate and adaptive antiviral immune responses. Depending on their activation pattern, pDC responses may be either protective or detrimental to the host. Here, we summarize and discuss current knowledge regarding pDC implication in the physiopathology of mouse and human herpesvirus infections, and we discuss how pDC functions could be manipulated in immunotherapeutic settings to promote health over disease.

Regulation of rat and human T-cell immune response by pharmacologically modified dendritic cells

BACKGROUND

The central function of dendritic cells (DC) in inducing and preventing immune responses makes them ideal therapeutic targets for the induction of immunologic tolerance. In a rat in vivo model, we showed that dexamethasone-treated DC (Dex-DC) induced indirect pathway-mediated regulation and that CD4+CD25+ T cells were involved in the observed effects. The aim of the present study was to investigate the mechanisms underlying the acquired immunoregulatory properties of Dex-DC in the rat and human experimental systems.

METHODS

After treatment with dexamethasone (Dex), the immunogenicity of Dex-DC was analyzed in T-cell proliferation and two-step hyporesponsiveness induction assays. After carboxyfluorescein diacetate succinimidyl ester labeling, CD4+CD25+ regulatory T-cell expansion was analyzed by flow cytometry, and cytokine secretion was measured by ELISA.

RESULTS

In this study, we demonstrate in vitro that rat Dex-DC induced selective expansion of CD4+CD25+ regulatory T cells, which were responsible for alloantigen-specific hyporesponsiveness. The induction of regulatory T-cell division by rat Dex-DC was due to secretion of interleukin (IL)-2 by DC. Similarly, in human studies, monocyte-derived Dex-DC were also poorly immunogenic, were able to induce T-cell anergy in vitro, and expand a population of T cells with regulatory functions. This was accompanied by a change in the cytokine profile in DC and T cells in favor of IL-10.

CONCLUSION

These data suggest that Dex-DC induced tolerance by different mechanisms in the two systems studied. Both rat and human Dex-DC were able to induce and expand regulatory T cells, which occurred in an IL-2 dependent manner in the rat system.

Kinetics of dendritic cells reconstitution and costimulatory molecules expression after myeloablative allogeneic haematopoetic stem cell transplantation: implications for the development of acute graft-versus host disease

Allogeneic hematopoetic stem cell transplantation (HSCT) represents a unique opportunity to monitor the kinetics of reconstitution of dendritic cells (DCs) and their dynamics in distinct pathologies. We analyzed DCs reconstitution after myeloablative HSCT. We separately analyzed patients with acute GVHD. DCs were monitored from the earliest phase of hematopoetic reconstitution until day +365. Both myeloid DCs and plasmacytoid DCs appeared at earliest stages after engraftment and relative numbers within white blood cells compartment peaked between days 19-25 after HSCT. Their proportion then gradually declined and absolute numbers of both DC subsets remained lower than in controls during the whole follow-up. Patients with acute GVHD had significantly lower numbers of circulating DCs. Decrease in DC counts preceded onset of clinical symptoms by at least 24 h and was independent of corticosteroids administration. This study reveals quantification of plasmacytoid and myeloid DCs as a potential biomarker for the prediction of acute GVHD development.

Repeated social defeat activates dendritic cells and enhances Toll-like receptor dependent cytokine secretion

Stress hormones significantly impact dendritic cell (DC) activation and function, typically in a suppressive fashion. However, a social stressor termed social disruption (SDR) has been shown to induce an increase in inflammatory responses and a state of glucocorticoid resistance in splenic CD11b+ monocytes. These experiments were designed to determine the effects of SDR on DC activation, Toll-like receptor-induced cytokine secretion, and glucocorticoid sensitivity. Compared to cells obtained from control animals, splenic DCs from SDR mice displayed increased levels of MHC I, CD80, and CD44, indicative of an activated phenotype. In addition, DCs from SDR mice produced comparatively higher TNF-alpha, IL-6, and IL-10 in response to in vitro stimulation with LPS and CpG DNA. Increased amounts of TNF-alpha and IL-6 were also evident in SDR DC cultures stimulated with poly(I:C). Furthermore, as shown previously in CD11b+ monocytes, the CD11c+ DCs obtained from SDR mice were glucocorticoid resistant. Taken together, the data suggest that social stress, in the absence of any immune challenge, activates DCs, increases DC cytokine secretion in response to Toll-specific stimuli and renders DCs glucocorticoid resistant.

Handbook of experimental pharmacology "dendritic cells": the use of dexamethasone in the induction of tolerogenic DCs

Dendritic cells (DCs) have a central role in immune regulation, ranging from tolerance induction to the induction of specific immune responses. DCs serve as an essential link between innate and adaptive immunity. This broad range of powerful immune stimulatory as well as regulatory functions has made DCs as targets for vaccine development strategies. One approach to promote the tolerogenicity of DCs is to suppress their maturation by pharmacological agents, including glucocorticoids (GCs). In the present chapter we will review GCs used in vitro with cultured DCs, applied in vivo, or used to generate tolerogenic DCs for cellular therapy.

Circulating naïve and CD4+CD25high regulatory T cells in patients with autoimmune pancreatitis

OBJECTIVE

Autoimmune pancreatitis (AIP) is a new clinical entity of pancreatic disorder. There are several immunologic and histological abnormalities specific for the disease, including increased levels of serum IgG4 and infiltration of lymphocytes and IgG4-positive plasmacytes. The role of IgG4 is unclear. Recently, regulatory T cells (Tregs) have been reported to be involved in the development of various autoimmune diseases as well as B cell shifting to IgG4-producing plasmacytes. To clarify the role of Tregs in the pathophysiology of AIP, we analyzed circulating Tregs in AIP.

METHODS

We recruited 27 patients with AIP for this study. For comparison, we also recruited 23 patients with other pancreatic disease and 32 healthy subjects as controls. We analyzed Tregs as CD4+CD25high and CD4+CD25+CD45RA+ (naïve) from peripheral blood by flow cytometry.

RESULTS

In peripheral blood, CD4+CD25high Tregs were significantly increased in AIP patients (3.01% T 1.77%) compared with alcoholic chronic pancreatitis (CP) (1.65% T 0.58%), idiopathic CP (1.53% T0.56%), and healthy control (1.72% T 0.81%, P G 0.05). Naïve Tregs significantly decreased in AIP (0.32% T 0.22%) compared with healthy control (0.83% T 0.65%) and CP group (alcoholic and idiopathic CP; 0.52% T 0.40%, P G 0.05). In untreated AIP patients,the number of CD4+CD25high Tregs and IgG4 are correlated (R =0.53, P G 0.05).

CONCLUSIONS

Increased numbers of CD4+CD25high Tregs may influence IgG4 production in AIP, whereas decreased numbers of naïve Tregs may be involved in the pathogenesis of AIP.

Use of dendritic cells in drug selection, development and therapy

BACKGROUND

Dendritic cells (DC) have the unique ability to induce immunity against tumors and various pathogens or to promote tolerance in autoimmunity and transplantation. Hence, they are central to the regulation of immune responses.

OBJECTIVE/METHODS

Due to the unique tolerogenic ability of DC, understanding some of the key molecules that regulate DC function may help with targeting the relevant signals in DC as therapeutic options for many disease conditions. DC are also targets of drugs, and many of the anti-inflammatory and pharmaceutical agents used to prevent autoimmunity or inhibit graft rejection interfere with DC function.

RESULTS/CONCLUSION

The drug-induced changes in DC may provide information for the selection of drugs and further drug discovery along with the use of DC as adjuvant in the treatment of autoimmunity and prevention of graft rejection in transplantation.

Innate immune functions of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are specialized immune cells capable of producing large amounts of type I interferon (IFN) and other proinflammatory cytokines in response to viral infections. To date, a multicomponent cytoplasmic transductional-transcriptional complex and a spatiotemporal mechanism have been revealed in pDCs that mediate the rapid and robust IFN production after Toll-like receptor activation. Multiple regulatory mechanisms involving surface receptors, intracellular and exogenous factors as well as virally encoded molecules have been shown to modulate the IFN responses in these cells. The unique innate immune functions of pDCs are crucial both in infectious diseases and in autoimmune diseases. The recent research progress provides an in-depth understanding of the biology of pDCs and a sensible basis for future therapeutic interventions.

Pharmacologic approaches to composite tissue allograft

This article discusses the pharmacologic approaches and the most promising new compounds for composite tissue allograft tolerance. Although some approaches rely on a combination of immunosuppressive agents that act synergistically against rejection, other strategies use immunologic manipulation, including major histocompatibility complex matching, induction of chimerism, and use of monoclonal antibodies to abrogate the immune response. There is still a need, however, to reproduce these findings in species phylogenetically closer to humans. This may be the target of future research efforts, which may overcome the challenge of limb and face transplant rejection.

Prednisolone suppresses the function and promotes apoptosis of plasmacytoid dendritic cells

Organ transplant recipients are highly susceptible to viral infections early after transplantation. Plasmacytoid dendritic cells (PDC) play a major role in antiviral immunity. Therefore, we determined the numbers of circulating PDC after liver transplantation (LTX) and established the effects of immunosuppressive drugs on PDC survival and function. PDC were determined longitudinally in 13 LTX recipients treated with prednisone and cyclosporin or tacrolimus. Purified PDC were cultured with or without clinically relevant concentrations of cyclosporin, tacrolimus or prednisolone. Apoptosis induction was monitored by determination of active caspase-3, nuclear condensation and annexin-V/7AAD staining. After LTX, a 4-fold reduction in the number of circulating PDC was observed (p < 0.01), which recovered partially after discontinuation of prednisone treatment. In vitro, prednisolone induced apoptosis in PDC, while cyclosporin and tacrolimus did not. Higher doses of prednisolone were needed to induce apoptosis in Toll-like receptor (TLR)-stimulated PDC. However, non-apoptosis inducing concentrations of prednisolone suppressed interferon-alpha production, upregulation of co-stimulatory molecules and allo-stimulatory capacity of TLR-stimulated PDC. In conclusion, prednisolone induces apoptosis in PDC, which explains the decline in circulating PDC numbers after transplantation. Moreover, prednisolone suppresses the functions of TLR-stimulated PDC. Therefore, corticosteroid-free immunosuppressive therapy may reduce the number and severity of viral infections after transplantation.

Endotoxin modulates the capacity of CpG-activated liver myeloid DC to direct Th1-type responses

DC are believed to play important roles in the induction and regulation of immune responses in the liver, an organ implicated in peripheral tolerance. Since the liver is located downstream of the gut, it is constantly exposed to bacterial LPS. Our recent observations indicate that prior exposure to endotoxin modulates subsequent liver DC responses to this TLR4 ligand. In this study, we demonstrate that endotoxin modifies the capacity of mouse liver myeloid DC (MDC) activated by CpG (TLR9 ligand) to direct Th1-type responses. IL-12 production by liver MDC was significantly lower than that of spleen MDC following CpG or Imiquimod (R837; TLR7 ligand) activation in vitro. In addition, allogeneic T cells stimulated by CpG-activated liver MDC secreted significantly lower levels of IFN-gamma than T cells stimulated with CpG-activated spleen MDC. A similar effect on liver DC was observed in response to in vivo CpG administration. This effect may be explained by exposure of the DC to endotoxin, because LPS attenuated IL-12 production by CpG-stimulated liver MDC, both in vitro and in vivo. Moreover, attenuation of the response to CpG was not observed in liver MDC from TLR4-mutant (C3H/HeJ) mice, in which TLR4 signaling is impaired. These data suggest that endotoxin-induced 'cross-tolerance' to TLR ligands in liver DC may contribute to down-regulation of hepatic immune responses.

Tacrolimus treatment of plasmacytoid dendritic cells inhibits dinucleotide (CpG-)-induced tumour necrosis factor-alpha secretion

Tacrolimus is a widely used immunosuppressive agent. Although T cells are the main targets of these pharmacological drugs, antigen presentation may also be affected. Among antigen-presenting cells, plasmacytoid dendritic cells (PDCs) are the main source of type I interferons upon microbial challenge, and are involved in several diseases and autoimmune disorders. The aim of this study was to evaluate whether tacrolimus can modulate the function of PDCs in vitro. Maturation and function of PDCs was determined using flow cytometry, enzyme-linked immunosorbent assay and cytometry bead arrays. The effect of tacrolimus on PDCs was observed mainly when the cells were pretreated with the immunosuppressive agent before activation. Upon dinucleotide-oligodeoxynucleotide (CpG-ODN) activation, tacrolimus pretreated PDCs showed a significant reduction in the surface expression of co-stimulatory molecules and human leucocyte antigen D-related (HLA-DR) and secreted reduced levels of tumour necrosis factor (TNF)-alpha. These results show that tacrolimus treatment of PDCs impairs CpG-induced activation, which could affect the outcome of the immune response.

Regulatory dendritic cell therapy in organ transplantation

Dendritic cells (DCs) are uniquely well equipped antigen (Ag)-presenting cells. Their classic function was thought to be that of potent initiators of innate and adaptive immunity to infectious organisms and other Ags (including transplanted organs). Evidence has emerged, however, that DCs have a central and crucial role in determining the fate of immune responses toward either immunity or tolerance. This dichotomous function of DCs, coupled with their remarkable plasticity, renders them attractive therapeutic targets for immune modulation. In transplantation, much recent work has focused on the ability of DCs to silence immune reactivity in an Ag-specific manner in the hope of preventing rejection and diminishing reliance on potentially harmful immunosuppressive agents. Experimental strategies have included in vivo targeting of DCs, as well as ex vivo generation of regulatory (or tolerogenic) DCs with subsequent reinfusion (i.e. cell therapy). Different approaches to 'program' DC toward tolerogenic properties include genetic (transgene insertion), biologic (differential culture conditions, anti-inflammatory cytokine exposure) and pharmacologic manipulation. Recent data suggest a promising role for pharmacologic treatment as a means of generating potent regulatory DCs and have further stimulated speculation regarding their potential clinical application. Herein, we discuss evidence that the potential of regulatory DC therapy is considerable and that there are compelling reasons to evaluate it in the setting of organ transplantation in the near future.

Glucocorticoids severely impair differentiation and antigen presenting function of dendritic cells despite upregulation of Toll-like receptors

Glucocorticoids (GCs) are widely used as anti-inflammatory and immunosuppressive agents. Effects of GC have mainly been attributed to the suppression of T cells. Recently, several studies have indicated the role of dendritic cells (DC) in GC-mediated immunosuppression. We investigated the effect of GC on characteristics of DC. Given the crucial role of Toll-like receptor (TLR) triggering for the initiation of DC maturation program, we analyzed the expression of TLR2, 3, 4 by GC-treated DC. To extend our in vitro findings, we analyzed the distribution of DC subsets in the blood of patients treated with high-dose corticosteroids. DC differentiation in presence of GC was skewed to a qualitatively distinct population incapable of inducing an efficient immune response, whereas GC presence during the process of maturation significantly reduced DC IL-12 p70 and TNF production and T cell stimulatory function. Despite the fact that GC increased expression of TLR2, 3 and 4 on DC, their stimulation with TLR-derived signals did not induce maturation. Administration of high-dose GC to the patients with systemic autoimmunity induced a decrease of circulating myeloid DC and abrogated plasmacytoid DC. These findings provide further insights into the mechanisms of GC immunosuppressive functions and reveal additional mechanisms of their therapeutic efficiency.