Function Of Dendritic Cells Subsets Research Articles

Pulmonary Conventional Type 1 Langerin-Expressing Dendritic Cells Play a Role in Impairing Early Protective Immune Response against Cryptococcus neoformans Infection in Mice.

Lung dendritic cells (DC) are powerful antigen-presenting cells constituted by various subpopulations that differ in terms of their function and origin and differentially regulate cell-mediated antifungal immunity. The lung is the primary target organ of Cryptococcus neoformans and C. gattii infections, which makes it essential in the establishment of the first line of anti-cryptococcal defense. However, the lung-specific dynamics and function of DC subsets are poorly understood in cryptococcosis. In this study, we provide evidence for the in vivo function of a conventional langerin-expressing DC1 dendritic cell (LangDC1) population during the first week of intratracheal C. neoformans infection in mice. By using conditional depletion of LangDC1 after diphtheria toxin treatment of LangDTREGFP mice, we demonstrate that these animals better control the fungal infection and produce type 1 and 17 cytokines in the context of a type 2 immune response, favoring a predominance of iNOS over arginase-1 expression by pulmonary cells. Our results suggest that LangDC1 cells play a role in impairing immune response for the clearance of C. neoformans in the early stage of pulmonary infection.

Reduced frequencies and functional impairment of dendritic cell subsets and non-classical monocytes in myelodysplastic syndromes.

In myelodysplastic syndromes (MDS) the immune system is involved in pathogenesis as well as in disease progression. Dendritic cells (DC) are key players of the immune system by serving as regulators of immune responses. Their function has been scarcely studied in MDS and most of the reported studies didn’t investigate naturally occurring DC subsets. Therefore, we here examined the frequency and function of DC subsets and slan+ non-classical monocytes in various MDS risk groups. Frequencies of DC as well as of slan+ monocytes were decreased in MDS bone marrow compared to normal bone marrow samples. Transcriptional profiling revealed down-regulation of transcripts related to pro-inflammatory pathways in MDS-derived cells as compared to normal bone marrow. Additionally, their capacity to induce T-cell proliferation was impaired. Multidimensional mass cytometry showed that whereas healthy donor-derived slan+ monocytes supported Th1/Th17/Treg differentiation/expansion their MDS-derived counterparts also mediated substantial Th2 expansion. Our findings point to a role for an impaired ability of DC subsets to adequately respond to cellular stress and DNA damage in the immune escape and progression of MDS. As such, it paves the way toward potential novel immunotherapeutic interventions.

Abstract 3881: Distinguishing dendritic cell subtypes in the tumor microenvironment using MultiOmyxTM

Abstract Dendritic cells (DCs) are key initiators and regulators of the innate and adaptive immune responses. An emerging interest in cancer therapies is the capability to activate endogenous DCs to induce antigen specific T cell responses and thereby generate DC-based immunotherapies. Understanding the function and diversity of DC subsets in the tumor environment will help improve therapies developed for cancer treatment. DC subpopulations have been recognized in humans and categorized based on their phenotype and functional criteria. These DC subsets are classified based on biomarker expressions and include CD123+ plasmacytoid dendritic cells (pDCs), two types of classical dendritic cells CD141+Clec9A+CD11c+ HLADR+ conventional type 1 dendritic cells (cDC1), CD1c+CD11c+HLADR+ conventional type 2 dendritic cells (cDC2) and CD14+CD11c+CD209+ monocyte derived dendritic cells (Mo-DCs). To help understand the complexity of distinct subsets of DCs, their spatial distribution within the tumor microenvironment (TME), and correlation with other immune cells, multiplex immunohistochemistry using a panel of antibodies broad enough to differentiate and characterize multiple DC subsets and T cell populations will be used. MultiOmyxTM, a novel hyperplexed multi ”omic” technology, enables visualization and characterization of multiple biomarkers across multiple assays on a single 4μm tissue section. MultiOmyx protein immunofluorescence (IF) assays utilize a pair of directly conjugated Cyanine dye-labeled (Cy3, Cy5) antibodies per round of staining. Each round of staining is imaged and followed by novel dye inactivation chemistry, enabling repeated rounds of staining and deactivation for up to 60 protein biomarkers. In this study, a MultiOmyx hyperplexed IF assay will be utilized to distinguish different DC subset within a tumor. Biomarkers including CD11c, CD123, CD141, CleC9A, CD1c, DC-Lamp, DC-sign, HLADR, CD14, CD68, CD163, CD3, CD4, CD8, FOXP3 and PanCK protein expression from a single 4 µm FFPE section in order to identify different subsets of DCs in tumor tissue from patients with Melanoma, a cancer type in which immunotherapeutic treatment has had a transformative effect and become the dominant therapeutic approach. Hopefully, a greater understanding of the phenotypes and functions of dendritic cells subsets will result in new cancer immunotherapy strategies. Citation Format: Maricel C. Gozo, Vivek Reddy, Mate Nagy, Nickolas Attanasio, Naiyun Zhou, Sara Pollan, Erinn Parnell, Eric Leones, Judy Kuo, Anna Juncker-Jensen, Josette William Ragheb, Qingyan Au. Distinguishing dendritic cell subtypes in the tumor microenvironment using MultiOmyxTM [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3881.

Innate Functions of Dendritic Cell Subsets in Cardiac Allograft Tolerance.

Survival rates after heart transplant have significantly improved over the last decade. Nevertheless, long-term allograft viability after 10 years remains poor and the sequelae of transplant-associated immunosuppression increases morbidity. Although several studies have implicated roles for lymphocyte-mediated rejection, less is understood with respect to non-major histocompatibility, and innate immune reactivity, which influence graft viability. As immature and mature dendritic cells (DCs) engage in both Major Histocompatibility Complex (MHC)-dependent and MHC-independent immune responses, these cells are at the crossroads of therapeutic strategies that seek to achieve both allograft tolerance and suppression of innate immunity to the allograft. Here we review emerging roles of DC subsets and their molecular protagonists during allograft tolerance and allograft rejection, with a focus on cardiac transplant. New insight into emerging DC subsets in transplant will inform novel strategies for operational tolerance and amelioration of cardiac vasculopathy.

Impaired Autophagy in CD11b+ Dendritic Cells Expands CD4+ Regulatory T Cells and Limits Atherosclerosis in Mice.

Atherosclerosis is a chronic inflammatory disease. Recent studies have shown that dysfunctional autophagy in endothelial cells, smooth muscle cells, and macrophages, plays a detrimental role during atherogenesis, leading to the suggestion that autophagy-stimulating approaches may provide benefit. Dendritic cells (DCs) are at the crossroad of innate and adaptive immune responses and profoundly modulate the development of atherosclerosis. Intriguingly, the role of autophagy in DC function during atherosclerosis and how the autophagy process would impact disease development has not been addressed. Here, we show that the autophagic flux in atherosclerosis-susceptible Ldlr-/- (low-density lipoprotein receptor-deficient) mice is substantially higher in splenic and aortic DCs compared with macrophages and is further activated under hypercholesterolemic conditions. RNA sequencing and functional studies on selective cell populations reveal that disruption of autophagy through deletion of Atg16l1 differentially affects the biology and functions of DC subsets in Ldlr-/- mice under high-fat diet. Atg16l1 deficient CD11b+ DCs develop a TGF (transforming growth factor)-β-dependent tolerogenic phenotype and promote the expansion of regulatory T cells, whereas no such effects are seen with Atg16l1 deficient CD8α+ DCs. Atg16l1 deletion in DCs (all CD11c-expressing cells) expands aortic regulatory T cells in vivo, limits the accumulation of T helper cells type 1, and reduces the development of atherosclerosis in Ldlr-/- mice. In contrast, no such effects are seen when Atg16l1 is deleted selectively in conventional CD8α+ DCs and CD103+ DCs. Total T-cell or selective regulatory T-cell depletion abrogates the atheroprotective effect of Atg16l1 deficient DCs. In contrast to its proatherogenic role in macrophages, autophagy disruption in DCs induces a counter-regulatory response that maintains immune homeostasis in Ldlr-/- mice under high-fat diet and limits atherogenesis. Selective modulation of autophagy in DCs could constitute an interesting therapeutic target in atherosclerosis.

Dendritic cells in cancer immunology and immunotherapy.

Dendritic cells (DCs) are a diverse group of specialized antigen-presenting cells with key roles in the initiation and regulation of innate and adaptive immune responses. As such, there is currently much interest in modulating DC function to improve cancer immunotherapy. Many strategies have been developed to target DCs in cancer, such as the administration of antigens with immunomodulators that mobilize and activate endogenous DCs, as well as the generation of DC-based vaccines. A better understanding of the diversity and functions of DC subsets and of how these are shaped by the tumour microenvironment could lead to improved therapies for cancer. Here we will outline how different DC subsets influence immunity and tolerance in cancer settings and discuss the implications for both established cancer treatments and novel immunotherapy strategies.

Hippo/Mst signalling couples metabolic state and immune function of CD8α+ dendritic cells.

Dendritic cells orchestrate the crosstalk between innate and adaptive immunity. CD8α+ dendritic cells present antigens to CD8+ T cells and elicit cytotoxic T cell responses to viruses, bacteria and tumours 1 . Although lineage-specific transcriptional regulators of CD8α+ dendritic cell development have been identified 2 , the molecular pathways that selectively orchestrate CD8α+ dendritic cell function remain elusive. Moreover, metabolic reprogramming is important for dendritic cell development and activation3,4, but metabolic dependence and regulation of dendritic cell subsetsare largely uncharacterized. Here we use a data-driven systems biology algorithm (NetBID) to identify a role of the Hippo pathway kinases Mst1 and Mst2 (Mst1/2) in selectively programming CD8α+ dendritic cell function and metabolism. Our NetBID analysis reveals a marked enrichment of the activities of Hippo pathway kinases in CD8α+ dendritic cells relative to CD8α- dendritic cells. Dendritic cell-specific deletion of Mst1/2-but not Lats1 and Lats2 (Lats1/2) or Yap and Taz (Yap/Taz), which mediate canonical Hippo signalling-disrupts homeostasis and function of CD8+ T cells and anti-tumour immunity. Mst1/2-deficient CD8α+ dendritic cells are impaired in presentation of extracellular proteins and cognate peptides to prime CD8+ T cells, while CD8α- dendritic cells that lack Mst1/2 have largely normal function. Mechanistically, compared to CD8α- dendritic cells, CD8α+ dendritic cells exhibit much stronger oxidative metabolism and critically depend on Mst1/2 signalling to maintain bioenergetic activities and mitochondrial dynamics for their functional capacities. Further, selective expression of IL-12 by CD8α+ dendritic cells depends on Mst1/2 and the crosstalk with non-canonical NF-κB signalling. Our findings identify Mst1/2 as selective drivers of CD8α+ dendritic cell function by integrating metabolic activity and cytokine signalling, and highlight that the interplay between immune signalling and metabolic reprogramming underlies the unique functions of dendritic cell subsets.

Dendritic cell intrinsic IRF4 expression regulates production of regulatory cytokines during influenza virus infection

Abstract Lung resident dendritic cells (DCs) are a heterogeneous population with diverse roles in respiratory infection. The development and function of DC subsets are controlled by distinct transcription factors including IRF4, which regulates CD11b+ cDC2 development, migration, and function. CD11c-cre Irf4fl/fl mice (KO) with a deletion of Irf4 in DCs lack a subset (P1) of lung CD11b+ DCs while other DCs are present but lack IRF4. To test the hypothesis that DC intrinsic IRF4 regulates anti-viral responses, wild type (WT) and KO mice were infected with a sublethal dose of influenza A/PuertoRico/8/34. On days 3–8 post-infection, a novel flow cytometry scheme was used to assess numbers and functional responses of lung and mediastinal lymph node (mLN) DCs, including tissue DC subsets CD103+ and CD11b+ (P1, P2), and inflammatory monocyte-derived Ly6Chi DCs. In addition to lacking CD11b+P1 DCs, KO mice had increased numbers of lung CD103+DCs, a defect in migration of CD11b+P2 DCs to the mLN and reduced numbers of Ly6Chi DCs in the mLN. In WT mice, CD11b+P1 DCs mice produced IL-10, and CD103+DCs preferentially displayed a latent form of TGFβ (LAP) and expressed Itgb8 needed to retain surface LAP for TGFβ activation. KO CD103+DCs showed reduced expression of TGFβ-LAP and Itgb8. Thus, DC production of both IL-10 and TGFβ is deficient in infected KO mice. The reduction of regulatory cytokines is consistent with our earlier finding that infected KO mice harbor decreased numbers of Foxp3+ T regulatory and CD8+ T memory cells, yet greater numbers of effector IFNg+ influenza-specific CD8+ T cells. In sum, IRF4 differentially regulates lung DC subsets to promote regulatory cytokines, and this diversity balances the anti-viral immune response to influenza infection.

Transcriptional Profiling of Age-Associated Gene Expression Changes in Human Circulatory CD1c+ Myeloid Dendritic Cell Subset.

Immune dysfunction is a hallmark of aging and is thought to be responsible for the age-associated diseases. Dendritic cells (DCs) of the immune system function as initiators and regulators of the immune responses. Recent studies have highlighted the division of labor between various DC subsets. CD1c+ DC subset has emerged as a major inducer of CD4 T cell response. There is a scarcity of information regarding the age-associated changes in the functions of DC subsets in the elderly. Here, we investigated the changes in transcriptional profile of CD1c+ DC subset from healthy aged and young individuals using RNA sequencing. Our results suggest that majority of the genes in DCs are upregulated with age. Glucose transport, GPCR, and potassium channel genes are all upregulated in DCs from aged as compared to young indicating an enhanced activation state of DCs from aged individuals. The expression of histones, small nucleolar RNA H/ACA box (SNORA) and small nucleolar RNA C/D/box (SNORD), and long non-coding RNA (lncRNA) is also substantially upregulated in the DCs from aged. In contrast, the antigen-presenting and energy generating pathways are downregulated. In summary, DCs from aged subjects display an activated state coupled with reduced antigen presentation which may be responsible for age-associate immune dysfunction.

Experimental models to investigate the function of dendritic cell subsets: challenges and implications

The dendritic cell (DC) lineage is remarkably heterogeneous. It has been postulated that specialized DC subsets have evolved in order to select and support the multitude of possible T cell differentiation pathways. However, defining the function of individual DC subsets has proven remarkably difficult, and DC subset control of key T cell fates such as tolerance, T helper cell commitment and regulatory T cell induction is still not well understood. While the difficulty in assigning unique functions to particular DC subsets may be due to sharing of functions, it may also reflect a lack of appropriate physiological in-vivo models for studying DC function. In this paper we review the limitations associated with many of the current DC models and highlight some of the underlying difficulties involved in studying the function of murine DC subsets.

In Vitro and In Vivo Effects of Ketamine on Generation and Function of Dendritic Cells

The question about how intravenous anesthetic reagents affect the development and function of dendritic cell subsets still has no comprehensive answers. Bone marrow cells differentiated with FMS-like tyrosine kinase 3 ligand in vitro represented the steady-state dendritic cell subsets. The effects of ketamine on the generation and function of dendritic cell subsets were investigated. We found that dendritic cell subsets responded to the anesthetic reagent ketamine in several aspects: 1) The in vitro and in vivo development of plasmacytoid dendritic cells were inhibited by ketamine at high concentrations; 2) The endocytosis of dendritic cells were not influenced by ketamine at concentrations from 50 - 200 µM; 3) The maturation markers of conventional dendritic cells were not changed by ketamine upon LPS or CpG stimulation, although the cytokines mRNA profiles were affected; 4) The allogenic-stimulatory activity of dendritic cells was suppressed by ketamine. In conclusion, ketamine hampered plasmacytoid dendritic cell subset development both in vivo and in vitro. The dendritic cells maturation and downstream responses towards different toll-like receptor stimuli were differently regulated by ketamine treatment.

Chemokine-mediated distribution of dendritic cell subsets in renal cell carcinoma

BackgroundRenal cell carcinoma (RCC) represents one of the most immunoresponsive cancers. Antigen-specific vaccination with dendritic cells (DCs) in patients with metastatic RCC has been shown to induce cytotoxic T-cell responses associated with objective clinical responses. Thus, clinical trials utilizing DCs for immunotherapy of advanced RCCs appear to be promising; however, detailed analyses concerning the distribution and function of DC subsets in RCCs are lacking.MethodsWe characterized the distribution of the different immature and mature myeloid DC subsets in RCC tumour tissue and the corresponding normal kidney tissues. In further analyses, the expression of various chemokines and chemokine receptors controlling the migration of DC subsets was investigated.ResultsThe highest numbers of immature CD1a+ DCs were found within RCC tumour tissue. In contrast, the accumulation of mature CD83+/DC-LAMP+ DCs were restricted to the invasive margin of the RCCs. The mature DCs formed clusters with proliferating T-cells. Furthermore, a close association was observed between MIP-3α-producing tumour cells and immature CCR6+ DC recruitment to the tumour bed. Conversely, MIP-3β and SLC expression was only detected at the tumour border, where CCR7-expressing T-cells and mature DCs formed clusters.ConclusionIncreased numbers of immature DCs were observed within the tumour tissue of RCCs, whereas mature DCs were found in increased numbers at the tumour margin. Our results strongly implicate that the distribution of DC subsets is controlled by local lymphoid chemokine expression. Thus, increased expression of MIP-3α favours recruitment of immature DCs to the tumour bed, whereas de novo local expression of SLC and MIP-3β induces accumulation of mature DCs at the tumour margin forming clusters with proliferating T-cells reflecting a local anti-tumour immune response.

The dendritic cell subsets function and the cytokines levels in plasma change in different period in patients with HBV infection

We studied the function of dendritic cells subsets and the cytokines levels in plasma in patients with different periods of returning (immune tolerance, hepatitis active and non-replicating period) and aimed to explore the possible reasons for HBV chronic infection. Thirty HBV infected patients in different stages of infection were enrolled and divided into three groups: the immune tolerance group (10 cases), the hepatitis active group (10 cases), and the non-replicating group (10 cases). Ten healthy people were enrolled and served as controls. Blood from the patients and controls were collected and the dendritic cells subsets function (The cytokine levels in different groups) were analyzed using statistical method. The total IL-12 output and single nucleus IL-12 output of the total HBV infected patients were lower than that of the healthy control group (P value less than 0.01). The total IFNa output and single nucleus IFNa output of the total HBV infected patients had no significant difference between the total HBV infected patients and the healthy controls (P value more than 0.05). The total IL-12 output of the healthy control group was higher than that in others 3 groups of the HBV infected patients. (Z = -3.039, -2.967 ,-2.949, P value less than 0.01) and the single nucleus IL-12 output of the healthy control group was also higher than that in others 3 groups of the HBV infected patients. (Z =-3.027, -2.671 , -2.863, P value less than 0.01) . The total IFNa output and the single nucleus IFNa output of the healthy control group was higher than that in the hepatitis active group of HBV infected patients (Z = -3.016, -3.176, P value less than 0.01). While the plasma IFNa cytokine levels in the 3 HBV infection groups were higher than in the healthy control group (Z = -2.967, -2.896, -3.054, P value less than 0.01). Difference existed between the function of dendritic cells subsets and the IFNa levels in different returning periods of HBV infected patients. The function of dendritic cells subsets has no significant difference in HBV patients with different periods of returning. The flawed function of dendritic cells subsets and the abnormal IFNa level may be one of the reasons for chronic HBV infection.

Lack of Retinoic Acid Leads to Increased Langerin-Expressing Dendritic Cells in Gut-Associated Lymphoid Tissues

Retinoic acid (RA) is a crucial factor for maintaining homeostasis in the gut, including lymphocyte homing, immunoglobulin (Ig) A production, and T regulatory cells (Treg) and T helper cell 17 (T(H)17) generation. Until now, most attention has focused on the function of dendritic cells (DCs) to initiate adaptive immunity including T and B lymphocytes through RA. To investigate the effects of RA on DCs of gut-associated lymphoid tissue (GALT), we analyzed the phenotype and function of DC subsets from GALT of vitamin A-deficient (VAD) mice. VAD mice were prepared by feeding them a VAD diet over 12 weeks from gestational days 10-14. Here, we report that tremendous increase of langerin(+) DCs occurred in the mesenteric lymph nodes (MLNs) and gut lamina propria of VAD mice dependent on CCR7 signaling. Langerin(+) DCs have phenotypes more similar to those of bone marrow-derived dermal langerin(+) DCs than epidermal Langerhans cells. Moreover, RA receptor antagonists enhance the differentiation of langerin(+) DCs from mouse and human precursors of bone marrow and peripheral blood. Langerin(+) DCs were highly differentiated but less inflammatory than langerin(-) DCs of MLNs of VAD mice. Moreover, tolerance to orally delivered antigen was completely abrogated by depletion of langerin(+) DCs in the VAD mice. These results suggest that generation of langerin(+) DCs in the GALT is tightly regulated by RA and that the microenvironment of tissues determines the phenotype of DCs.

Deficiency of Type I IFN Receptor in Lupus-Prone New Zealand Mixed 2328 Mice Decreases Dendritic Cell Numbers and Activation and Protects from Disease

Type I IFNs are potent regulators of innate and adaptive immunity and are implicated in the pathogenesis of systemic lupus erythematosus. Here we report that clinical and pathological lupus nephritis and serum anti-nuclear Ab levels are greatly attenuated in New Zealand Mixed (NZM) 2328 mice deficient in type I IFN receptors (IFNAR). To determine whether the inflammatory environment in NZM 2328 mice leads to IFNAR-regulated changes in dendritic cells (DC), the number, activation, and function of DC subsets were compared in 2- and 5-mo-old (clinically healthy) female NZM and NZM-IFNAR(-/-) mice. Numbers of activated CD40(high) plasmacytoid DC (pDC) were significantly increased in renal lymph nodes of 2-mo-old NZM but not NZM-IFNAR(-/-) mice, suggesting an early IFNAR-dependent expansion and activation of pDC at disease sites. Relative to NZM spleens, NZM-IFNAR(-/-) spleens in 5-mo-old mice were significantly decreased in size and contained reduced numbers of conventional DC subsets, but not pDC. Splenic and renal lymph node NZM-IFNAR(-/-) DC analyzed directly ex vivo expressed significantly less CD40, CD86, and PDL1 than did NZM DC. Upon activation with synthetic TLR9 ligands in vitro, splenic NZM-IFNAR(-/-) DC produced less IL-12p40/70 and TNF-alpha than did NZM DC. The limited IFNAR(-/-) DC response to endogenous activating stimuli correlated with reduced numbers of splenic activated memory CD4(+) T cells and CD19(+) B cells in older mice. Thus, IFNAR signaling significantly increases DC numbers, acquisition of Ag presentation competence, and proinflammatory function before onset of clinically apparent lupus disease.

Phenotype changes and impaired function of dendritic cell subsets in patients with sepsis: a prospective observational analysis

IntroductionPatients with sepsis often demonstrate severely impaired immune responses. The hallmark of this state of immunoparalysis is monocytic deactivation characterized by decreased human leukocyte antigen (HLA)-DR expression and reduced production of proinflammatory cytokines. Recently, diminished numbers of dendritic cells (DCs) were reported in patients with sepsis. However, little is known about DC phenotype and function in human sepsis. We therefore compared phenotypic and functional changes in monocyte and DC subsets in patients with sepsis and immunoparalysis.MethodsIn a prospective observational analysis, 16 consecutive patients with severe sepsis and septic shock (age 59.2 ± 9.7 years, 13 male, Sequential Organ Failure Assessment score 6.1 ± 2.7) and immunoparalysis (monocytic HLA-DR expression < 5,000 antibodies/cell) and 16 healthy volunteers were included. Peripheral blood DC counts, HLA-DR expression and ex vivo cytokine production were evaluated in comparison with monocyte subsets over time.ResultsAt baseline, a profound reduction in the numbers of myeloid DCs (MDCs), plasmacytoid DCs (PDCs), and CD14dimCD16positive monocytes was observed in sepsis whereas CD14brightCD16negative and CD14brightCD16positive monocyte numbers were increased. HLA-DR expression was reduced on all monocyte and DC subsets. Production of proinflammatory cytokines and intracellular cytokine staining in response to lipopolysaccharide and lipoteichoic acid was impaired in monocyte subsets and MDCs, whereas IL-10 secretion was increased. IFNα response by stimulated PDCs was significantly decreased compared with controls. At day 28, HLA-DR expression and cytokine production of DC and monocyte subsets remained lower in septic patients compared with controls.ConclusionsIn sepsis, long-lasting functional deactivation is common to all circulating monocyte and DC subsets. In addition to decreased peripheral blood DC counts, functional impairment of antigen-presenting cells may contribute to an impaired antimicrobial defense in sepsis.

Distinct functional capacities of mouse thymic and splenic dendritic cell populations

Dendritic cells (DC) are antigen-presenting cells that activate naive T cells. Murine DC are a heterogeneous population and can be subdivided into distinct subsets with different immune regulatory functions, namely the conventional DC (cDC), which include the CD8(+)Sirpalpha(-) and CD8(-)Sirpalpha(+) DC, and the plasmacytoid DC (pDC). In this study, the phenotype and function of DC subsets in both the thymus and spleen were compared. Significant differences between the thymic and splenic DC were observed in the expression of genes encoding chemokine receptors (CCRs), toll-like receptors (TLRs) and chemokines. Thymic DC expressed high levels of genes encoding a unique set of chemokines (CCL17 and CCL22) known to be important for T-cell development. Moreover, the capacity of the DC from the two organs to produce IL-6, IFN-alpha and IL-12p70 in response to the TLR 9 agonist CpG differed markedly, indicating intrinsic functional differences between subsets with similar surface phenotype. These results indicate that the microenvironment is an important factor that contributes to the functional specification of DC subsets in different lymphoid tissues.

Control of myeloid dendritic cell differentiation and function by CD1d-restricted (NK) T cells.

While regulating a wide variety of immunologic responses, the precise immunologic functions of CD1d-restricted (NK) T cells are not well defined. Notably, In vitro activation of human NK T cell clones results in the secretion of multiple cytokines important for the recruitment and differentiation of myeloid dendritic cells (DC). Once differentiated, these DC strongly activate NK T cells. In humans, CD1d is expressed by myeloid DC and on tumor cells of this lineage. Another specialized myeloid antigen presenting cell, the epithelioid histiocyte seen in granulomatous inflammation, also expresses CD1d. Because myeloid DC are important regulators of Th1/Th2 T cell responses, cross talk between human NK T cells and myeloid DC would be expected to have significant impact on many immune responses. Consistent with this hypothesis, NK T cells are required for myeloid DC-controlled antitumor responses in mice, and regulate diabetes in nonobese diabetic (NOD) mouse by locally controlling the frequency and function of DC subsets. Thus, regulation of myeloid DC by NK T cells controls both the transition from innate to adaptive immunity and the Th-phenotype of subsequent T cell responses.

IL-12 induction by a TH1-inducing adjuvant in vivo: dendritic cell subsets and regulation by IL-10.

IL-12 induction is critical for immune responses against many viruses and intracellular bacterial pathogens. Recent studies suggest that IL-12-secreting dendritic cells (DC) are potent Th1-inducing APC. However, controversy exists concerning the function of DC subsets. Murine studies have suggested that CD8(+) DC preferentially induce Th1 responses, whereas CD8(-) DC induce Th2 development; in this model, different DC subsets prime different responses. Alternatively, the propensity of DC subsets to prime a Th1 response could depend upon the type of initial stimulus. We used a prototypic Th1-inducing adjuvant, heat-killed Brucella abortus (HKBA) to assess stimulation of DC subsets, relationship between Ag burden and IL-12 production, and down-regulation of DC subset IL-12 production by IL-10. In this study, we show that DC were sole producers of IL-12, although most HKBA uptake was by splenic macrophages and granulocytes. More CD8(-) than CD8(+) DC produced IL-12 after HKBA challenge, whereas only CD8(+) DC produced IL-12 after injection of another Th1-promoting microbial substance, soluble Toxoplasma gondii Ags. Studies in IL-10-deficient mice revealed that IL-10 down-regulates frequency and duration of IL-12 production by both DC subsets. In the absence of IL-10, IL-12 expression is enabled in CD11c(low) cells, but not in macrophages or granulocytes. These findings support the concept of DC as the major IL-12 producers in spleens, but challenge the notion that CD8(+) and CD8(-) DC are destined to selectively induce Th1 or Th2 responses, respectively. Thus, the nature of the stimulating substance is important in determining which DC subsets are activated to produce IL-12.