Dendritic cells and their potential implication in pathology and treatment of rheumatoid arthritis

Neuro-Immunomodulatory Potential of Nanoenabled 4D Bioprinted Microtissue for Cartilage Tissue Engineering

Cartilage defects trigger post-traumatic inflammation, leading to a catabolic metabolism in chondrocytes and exacerbating cartilage degradation. Current treatments aim to relieve pain but fail to target the inflammatory process underlying osteoarthritis (OA) progression. Here, a human cartilage microtissue (HCM) nanoenabled with ibuprofen-loaded poly(lactic-co-glycolic acid) nanoparticles (ibu-PLGA NPs) is 4D-bioprinted to locally mitigate inflammation and impair nerve sprouting. Under an in vitro inflamed environment, the nanoenabled HCM exhibits chondroprotective potential by decreasing the interleukin (IL)1β and IL6 release, while sustaining extracellular matrix (ECM) production. In vivo, assessments utilizing the air pouch mouse model affirm the nanoenabled HCM non-immunogenicity. Nanoenabled HCM-derived secretomes do not elicit a systemic immune response and decrease locally the recruitment of mature dendritic cells and the secretion of multiple inflammatory mediators and matrix metalloproteinases when compared to inflamed HCM condition. Notably, the nanoenabled HCM secretome has no impact on the innervation profile of the skin above the pouch cavity, suggesting a potential to impede nerve growth. Overall, HCM nanoenabled with ibu-PLGA NPs emerges as a potent strategy to mitigate inflammation and protect ECM without triggering nerve growth, introducing an innovative and promising approach in the cartilage tissue engineering field.

Regulation of Myeloid Dendritic Cells by Synthetic and Natural Compounds for the Treatment of Rheumatoid Arthritis

Different subsets of dendritic cells (DCs) participate in the development of rheumatoid arthritis (RA). In particular, myeloid DCs play a key role in the generation of autoreactive T and B cells. Herein, we undertook a literature review on those synthetic and natural compounds that have therapeutic efficacy/potential for RA and act through the regulation of myeloid DCs. Most of these compounds inhibit both the maturation of DCs and their secretion of inflammatory cytokines and, subsequently, alter the downstream T-cell response (suppression of Th1 and Th17 responses while expanding the Treg response). The majority of the synthetic compounds are approved for the treatment of patients with RA, which is consistent with the importance of DCs in the pathogenesis of RA. All of the natural compounds are derived from plants. Their DC-modulating effect has been demonstrated both in vitro and in vivo. In addition, these natural products ameliorate arthritis in rodents and are potential therapeutics for human RA.

Simultaneous transduction of dendritic cells with A20 and BTLA genes stimulates the development of stable and efficient tolerogenic dendritic cells and induces regulatory T cells

BACKGROUND

This study investigated the potential of simultaneous overexpression of A20 and B- and T-lymphocyte attenuator (BTLA) genes in dendritic cells (DCs) to develop a tolerogenic phenotype in DCs and investigate their capabilities for induction of immunosuppression.

METHODS

Plasmid vectors were designed harboring A20, BTLA, and A20 + BTLA genes and were transfected to HEK 293T cells to produce lentiviruses. DCs were transduced by the gene carrying viruses and evaluated for the surface expression of MHCII, CD40, and CD86 molecules by flow-cytometry. The mRNA expression of A20, BTLA, and CCR7 were determined. Mixed-lymphocyte reaction was conducted to evaluate the T cell stimulation potency and ELISA was used to measure the production of IL-10, TGF-β, and TNF-α. The potential of DCs for migration to lymph nodes and Treg induction were assessed by in vivo experiments.

RESULTS

Transduction of DCs resulted in significantly decreased surface expression of CD40 and CD86 co-stimulators and upregulated A20, BTLA, and CCR7 mRNA expression. The IL-10 and TGF-β levels were enhanced significantly in the supernatant of LPS-treated DCs transduced with A20 + BTLA-containing virus group relative to the DCs transduced with pCDH vectors. DCs transduced with A20 + BTLA harboring vectors had higher migratory potential to mouse lymph nodes and caused the development of higher numbers of Treg cells compared with the DCs transduced with pCDH vectors.

CONCLUSIONS

Simultaneous overexpression of A20 and BTLA genes in DCs caused development of tolerogenic DCs with a promoted potential in induction of Treg cells, accompanied by remarkable stability after inflammatory stimulation. All these offer a promising potential of such DCs in treating autoimmune and inflammatory disorders.

TonEBP in dendritic cells mediates pro-inflammatory maturation and Th1/Th17 responses

Dendritic cells (DCs) are potent antigen-presenting cells that link the innate and adaptive immune responses; as such they play pivotal roles in initiation and progression of rheumatoid arthritis (RA). Here, we report that the tonicity-responsive enhancer-binding protein (TonEBP or NFAT5), a Rel family protein involved in the pathogenesis of autoimmune disease and inflammation, is required for maturation and function of DCs. Myeloid cell-specific TonEBP deletion reduces disease severity in a murine model of collagen-induced arthritis; it also inhibits maturation of DCs and differentiation of pathogenic Th1 and Th17 cells in vivo. Upon stimulation by TLR4, TonEBP promotes surface expression of major histocompatibility complex class II and co-stimulatory molecules via p38 mitogen-activated protein kinase. This is followed by DC-mediated differentiation of pro-inflammatory Th1 and Th17 cells. Taken together, these findings provide mechanistic basis for the pathogenic role of TonEBP in RA and possibly other autoimmune diseases.

Blocking Matrix Metalloproteinase-9 Abrogates Collagen-Induced Arthritis via Inhibiting Dendritic Cell Migration

Trafficking of dendritic cells (DCs) to lymph nodes (LNs) to present Ags is a crucial step in the pathogenesis of rheumatoid arthritis (RA). Matrix metalloproteinase-9 (MMP-9) is the key molecule for DC migration. Thus, blocking MMP-9 to inhibit DC migration may be a novel strategy to treat RA. In this study, we used anti-MMP-9 Ab to treat collagen-induced arthritis (CIA) in DBA/1J mice and demonstrated that anti-MMP-9 Ab treatment significantly suppressed the development of CIA via the modulation of DC trafficking. In anti-MMP-9 Ab-treated CIA mice, the number of DCs in draining LNs was obviously decreased. In vitro, anti-MMP-9 Ab and MMP-9 inhibitor restrained the migration of mature bone marrow-derived DCs in Matrigel in response to CCR7 ligand CCL21. In addition, blocking MMP-9 decreased T and B cell numbers in LNs of CIA mice but had no direct influence on the T cell response to collagen II by CD4⁺ T cells purified from LNs or spleen. Besides, anti-MMP-9 Ab did not impact on the expression of MHC class II, CD40, CD80, CD86, and chemokine receptors (CCR5 and CCR7) of DCs both in vivo and in vitro. Furthermore, we discovered the number of MMP-9^-/- DCs trafficking from footpads to popliteal LNs was dramatically reduced as compared with wild type DCs in both MMP-9^-/- mice and wild type mice. Taken together, these results indicated that DC-derived MMP-9 is the crucial factor for DC migration, and blocking MMP-9 to inhibit DC migration may constitute a novel strategy of future therapy for RA and other similar autoimmune diseases.

Update on Dendritic Cell-Induced Immunological and Clinical Tolerance

Dendritic cells (DCs) as highly efficient antigen-presenting cells are at the interface of innate and adaptive immunity. As such, they are key mediators of immunity and antigen-specific immune tolerance. Due to their functional specialization, research efforts have focused on the characterization of DCs subsets involved in the initiation of immunogenic responses and in the maintenance of tissue homeostasis. Tolerogenic DCs (tolDCs)-based therapies have been designed as promising strategies to prevent and control autoimmune diseases as well as allograft rejection after solid organ transplantation (SOT). Despite successful experimental studies and ongoing phase I/II clinical trials using autologous tolDCs in patients with type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and in SOT recipients, additional basic research will be required to determine the optimal DC subset(s) and conditioning regimens for tolDCs-based treatments in vivo. In this review, we discuss the characteristics of human DCs and recent advances in their classification, as well as the role of DCs in immune regulation and their susceptibility to in vitro or in vivo manipulation for the development of tolerogenic therapies, with a focus on the potential of tolDCs for the treatment of autoimmune diseases and the prevention of allograft rejection after SOT.

Dendritic Cells from Rheumatoid Arthritis Patient Peripheral Blood Induce Th17 Cell Differentiation via miR-363/Integrin αv/TGF-β Axis

Dendritic cells (DCs) are critical regulators of immune responses. This study was to observe the effect of DCs from peripheral blood on the differentiation of Th17 in patients with rheumatoid arthritis (RA). Peripheral blood samples were collected from 30 patients with RA and 20 healthy controls, respectively. Flow cytometry results showed that in contrast to Treg cells, the proportion of Th17 cells in T cells and the Th17/Treg ratio were both increased in patients with RA. The RT-PCR results showed that Foxp3、ROR γt and miR-363 expression in PBMC of patients with RA were reduced, but the ITGAV expression was increased, which was negatively related to miR-363 expression. IL-17, TGF-β and IL-6 levels detected by ELISA were increased in peripheral blood serum of patients with RA. Moreover, we noted that the CD11C⁺ αν⁺ /CD11C⁺ DCs ratio was obvious increased in patients with RA and has positive correlation to the Th17/Treg ratio. In cocultured system, Th17 cell differentiation was significantly inhibited in the presence of ITGF-β suggesting that Th17 cell differentiation was controlled by active TGF-β (aTGF-β). After DCs transfecting with miR-363 mimics and cocultured with T cells, Th17 cell number, IL-17 level and ROR-γt expression were significantly reduced in the presence of latent TGF-β (ITGF-β). In addition, the integrin αv protein expression was both reduced in the presence of aTGF-β or ITGF-β. These data demonstrated that DCs induced Th17 cell differentiation through miR-363/Integrin αv/TGF-β pathway in patients with RA.

The inflammatory role of phagocyte apoptotic pathways in rheumatic diseases

Rheumatoid arthritis affects nearly 1% of the world's population and is a debilitating autoimmune condition that can result in joint destruction. During the past decade, inflammatory functions have been described for signalling molecules classically involved in apoptotic and non-apoptotic death pathways, including, but not limited to, Toll-like receptor signalling, inflammasome activation, cytokine production, macrophage polarization and antigen citrullination. In light of these remarkable advances in the understanding of inflammatory mechanisms of the death machinery, this Review provides a snapshot of the available evidence implicating death pathways, especially within the phagocyte populations of the innate immune system, in the perpetuation of rheumatoid arthritis and other rheumatic diseases. Elevated levels of signalling mediators of both extrinsic and intrinsic apoptosis, as well as the autophagy, are observed in the joints of patients with rheumatoid arthritis. Furthermore, risk polymorphisms are present in signalling molecules of the extrinsic apoptotic and autophagy death pathways. Although research into the mechanisms underlying these pathways has made considerable progress, this Review highlights areas where further investigation is particularly needed. This exploration is critical, as new discoveries in this field could lead to the development of novel therapies for rheumatoid arthritis and other rheumatic diseases.

Maturation and cytokine production potential of dendritic cells isolated from rheumatoid arthritis patients peripheral blood and induced in vitro

BACKGROUND

Since dendritic cells (DC) are involved in the development of autoimmune inflammation, researchers consider DC both as target cells for specific therapy of rheumatoid arthritis (RA) and as candidate cells for the development of cell-based methods to treat autoimmune diseases. The development of treatment strategies requires comprehensive research into the quantitative and qualitative characteristics of DC subtypes both ex vivo from RA patients and in vitro, to determine the possibility of inducing functionally mature DC in RA.

OBJECTIVE

To study the phenotypic and functional properties of myeloid (mDC) and plasmacytoid (pDC) DC isolated from the peripheral blood of patients with RA and induced in vitro.

MATERIALS AND METHODS

Blood samples were obtained from RA patients and healthy donors. Immature DC in the whole blood and in vitro induced DC were characterized by the positive expression of CD80, CD83, CCR7, IL-10, IL-4, IL-12 and IFN-α. R848 and lipopolysaccharide were used to determine DC maturation ability. From PBMCs of RA patients and health donors DCs with myeloid (imDC) and plasmacytoid (ipDC) phenotype were induced.

RESULTS

The relative count of mDC in the peripheral blood between studied groups did not differ. pDC count was significantly lower for RA patients. DC from RA patients were characterized by low expression levels of CD80 and CD83 on both populations cells and high expression of CCR7 only on pDC. An increase in pDC producing IL-12 and IFN-α and a decrease in mDC and pDC producing IL-4 and IL-10 were shown in RA. imDC and ipDC obtained from RA patients according to their phenotype and cytokine profile did not differ from those obtained from healthy donors.

CONCLUSIONS

There is an imbalance between subpopulations of DC in the peripheral blood of RA patients. DC of RA patients are less mature. The data suggest the involvement of DC in RA pathogenesis and confirm DC participation in balance shift towards Th1-type immune responses. At the same time, in vitro induced RA DC are phenotypically and functionally competent.

Tolerogenic dendritic cells for reprogramming of lymphocyte responses in autoimmune diseases

Dendritic cells (DCs) control immune responses by driving potent inflammatory actions against external and internal threats while generating tolerance to self and harmless components. This duality and their potential to reprogram immune responses in an antigen-specific fashion have made them an interesting target for immunotherapeutic strategies to control autoimmune diseases. Several protocols have been described for in vitro generation of tolerogenic DCs (tolDCs) capable of modulating adaptive immune responses and restoring tolerance through different mechanisms that involve anergy, generation of regulatory lymphocyte populations, or deletion of potentially harmful inflammatory T cell subsets. Recently, the capacity of tolDCs to induce interleukin (IL-10)-secreting regulatory B cells has been demonstrated. In vitro assays and rodent models of autoimmune diseases provide insights to the molecular regulators and pathways enabling tolDCs to control immune responses. Here we review mechanisms through which tolDCs modulate adaptive immune responses, particularly focusing on their suitability for reprogramming autoreactive CD4⁺ effector T cells. Furthermore, we discuss recent findings establishing that tolDCs also modulate B cell populations and discuss clinical trials applying tolDCs to patients with autoimmune diseases.

Apigenin, a potent suppressor of dendritic cell maturation and migration, protects against collagen-induced arthritis

This study aimed to investigate whether apigenin (API) suppresses arthritis development through the modulation of dendritic cell functions. Bone marrow-derived dendritic cells (BMDCs) were stimulated in vitro with lipopolysaccharide (LPS) and treated with API for 24 hrs; DC functions, including phenotype expressions, cytokine secretion, phagocytosis and chemotaxis, were then investigated. The effects of API on collagen-induced arthritis (CIA) were examined in vivo, and purified DCs from the lymph nodes (LNs) of API-treated CIA mice were analysed for phenotypes and subsets. In in vitro, API efficiently restrained the phenotypic and functional maturation of LPS-stimulated BMDCs while maintaining phagocytotic capabilities. Moreover, API inhibited the chemotactic responses of LPS-stimulated BMDCs, which may be related to the depressive effect on chemokine receptor 4 (CXCR4). In in vivo, API treatment delayed the onset and reduced the severity of arthritis in CIA mice, and diminished secretion of pro-inflammatory cytokines in the serum and supernatants from the LN cells of the CIA mice. Similar to the in vitro findings, the API-treated mice exhibited reduced expression of co-stimulatory molecules and major histocompatibility complex II on DCs. Furthermore, API treatment strongly down-regulated the number of Langerhans cells, but not plasmacytoid DCs (pDCs) in LNs, which may be related to the depressive effect of API on the expression of CXCR4 on DCs of peripheral blood. These data provide new insight into the mechanism of action of API on arthritis and indicate that the inhibition of maturation and migration of DCs by API may contribute to its immunosuppressive effects.

FTY720 Abrogates Collagen-Induced Arthritis by Hindering Dendritic Cell Migration to Local Lymph Nodes

Because dendritic cells (DCs) play critical roles in the pathogenesis of rheumatoid arthritis, modulation of their functions could serve as a novel therapy. In this study, we demonstrated that FTY720 treatment significantly suppressed the incidence and severity of collagen-induced arthritis (CIA) in DBA/1J mice via the modulation of DC functions. In FTY720-treated CIA mice, a decrease in the number of DCs in local draining lymph nodes (LNs) was observed. In vitro, FTY720 inhibited the trafficking of LPS-stimulated bone marrow-derived DCs (BMDCs). Decreased secretion of CCL19 and downregulation of CCR7 on DCs may explain the mechanisms underlying the impairment of DC migration induced by FTY720. In a DC-induced mouse arthritis model, FTY720 treatment also suppressed the incidence and severity of arthritis, which was correlated with a decrease in the migration of injected BMDCs to draining LNs. Although lower levels of costimulatory molecules (CD40, CD80, and CD86) and I-A(q) expressed on LN DCs were observed in FTY720-treated mice, in vitro analysis showed no effect of FTY720 on LPS-stimulated BMDC maturation. Furthermore, LN cells from FTY720-treated CIA mice displayed diminished production of proinflammatory cytokines in response to collagen II and Con A stimulation. In addition, the ratio of Th1/Th2 in the draining LNs of mice with DC-induced arthritis was decreased upon FTY720 treatment. This finding was consistent with the fact that FTY720 suppressed IL-12p70 production in cultured BMDCs. Taken together, these results indicate that inhibition of DC migration by FTY720 may provide a novel approach in treating autoimmune diseases such as rheumatoid arthritis.

Targeting BCL2 family in human myeloid dendritic cells: a challenge to cure diseases with chronic inflammations associated with bone loss

Rheumatoid arthritis (RA) and Langerhans cell histiocytosis (LCH) are common and rare diseases, respectively. They associate myeloid cell recruitment and survival in inflammatory conditions with tissue destruction and bone resorption. Manipulating dendritic cell (DC), and, especially, regulating their half-life and fusion, is a challenge. Indeed, these myeloid cells display pathogenic roles in both diseases and may be an important source of precursors for differentiation of osteoclasts, the bone-resorbing multinucleated giant cells. We have recently documented that the proinflammatory cytokine IL-17A regulates long-term survival of DC by inducing BCL2A1 expression, in addition to the constitutive MCL1 expression. We summarize bibliography of the BCL2 family members and their therapeutic targeting, with a special emphasis on MCL1 and BCL2A1, discussing their potential impact on RA and LCH. Our recent knowledge in the survival pathway, which is activated to perform DC fusion in the presence of IL-17A, suggests that targeting MCL1 and BCL2A1 in infiltrating DC may affect the clinical outcomes in RA and LCH. The development of new therapies, interfering with MCL1 and BCL2A1 expression, to target long-term surviving inflammatory DC should be translated into preclinical studies with the aim to increase the well-being of patients with RA and LCH.

Immunological effects of Oenothein B, an ellagitannin dimer, on dendritic cells

Oenothein B is a unique macrocyclic ellagitannin dimer that has been found in various medicinal plants belonging to Onagraceae, Lythraceae, and Myrtaceae, with diverse biological activities. The immunological effects of tannins in terms of cytokine-release from macrophages and monocytes have been discussed, while the effects on other immunocompetent cells have been the subject of minimal investigation. We evaluated the immunomodulatory effects induced by tannin treatment in human dendritic cells (DCs), which play a critical role in the initial immune response, by measuring the changes in cytokine production, cell differentiation, and cell viability. Oenothein B showed significant down-regulation of the expression of cell surface molecules, CD1a and CD83, suggesting the inhibition of DC differentiation and/or maturation. The suppressive effect on DCs was associated with the induction of apoptosis without the activation of caspase-3/7, 8, and 9, and this was supported by the morphological features indicating significant nuclear condensation. Oenothein B also markedly suppressed the production of inflammatory cytokines, such as IL-1β and IL-6, in a dose-dependent manner. These data may, in part, be able to explain the traditional use of tannin-containing medicinal plants for the treatment of a variety of inflammatory diseases, including inflammatory bowel disease, celiac disease, and rheumatoid arthritis.

Fas-independent T-cell apoptosis by dendritic cells controls autoimmune arthritis in MRL/lpr mice

Background

Although autoimmunity in MRL/lpr mice occurs due to a defect in Fas-mediated cell death of T cells, the role of Fas-independent apoptosis in pathogenesis has rarely been investigated. We have recently reported that receptor activator of nuclear factor (NF)-κB ligand (RANKL)-activated dendritic cells (DCs) play a key role in the pathogenesis of rheumatoid arthritis (RA) in MRL/lpr mice. We here attempted to establish a new therapeutic strategy with RANKL-activated DCs in RA by controlling apoptosis of peripheral T cells. Repeated transfer of RANKL-activated DCs into MRL/lpr mice was tested to determine whether this had a therapeutic effect on autoimmunity.

Methods and Finding

Cellular and molecular mechanisms of Fas-independent apoptosis of T cells induced by the DCs were investigated by in vitro and in vivo analyses. We demonstrated that repeated transfers of RANKL-activated DCs into MRL/lpr mice resulted in therapeutic effects on RA lesions and lymphoproliferation due to declines of CD4⁺ T, B, and CD4⁻CD8⁻ double negative (DN) T cells. We also found that the Fas-independent T-cell apoptosis was induced by a direct interaction between tumor necrosis factor (TNF)-related apoptosis-inducing ligand-receptor 2 (TRAIL-R2) on T cells and TRAIL on Fas-deficient DCs in MRL/lpr mice.

Conclusion

These results strongly suggest that a novel Fas-independent apoptosis pathway in T cells maintains peripheral tolerance and thus controls autoimmunity in MRL/lpr mice.

Endogenous activation of adaptive immunity: tenascin-C drives interleukin-17 synthesis in murine arthritic joint disease

OBJECTIVE

Rheumatoid arthritis is characterized by persistent synovial inflammation and progressive joint destruction, which are mediated by innate and adaptive immune responses. Cytokine blockade successfully treats some patient subsets; however, ∼50% do not respond to this approach. Targeting of pathogenic T lymphocytes is emerging as an effective alternative/complementary therapeutic strategy, yet the factors that control T cell activation in joint disease are not well understood. Tenascin-C is an arthritogenic extracellular matrix glycoprotein that is not expressed in healthy synovium but is elevated in the rheumatoid joint, where high levels are produced by myeloid cells. Among these cells, tenascin-C expression is most highly induced in activated dendritic cells (DCs). The aim of this study was to examine the role of tenascin-C in this cell type.

METHODS

We systematically compared the phenotype of DCs isolated from wild-type mice or mice with a targeted deletion of tenascin-C by assessing cell maturation, cytokine synthesis, and T cell polarization.

RESULTS

Dendritic cells derived from tenascin-C-null mice exhibited no defects in maturation; induction of the class II major histocompatibility complex and the costimulatory molecules CD40 and CD86 was unimpaired. Dendritic cells that did not express tenascin-C, however, produced lower levels of inflammatory cytokines than did cells from wild-type mice and exhibited specific defects in Th17 cell polarization. Moreover, tenascin-C-null mice displayed ablated levels of interleukin-17 in the joint during experimental arthritis.

CONCLUSION

These data demonstrate that tenascin-C is important in DC-mediated polarization of Th17 lymphocytes during inflammation and suggest a key role for this endogenous danger signal in driving adaptive immunity in erosive joint disease.

Dendritic cell control of tolerogenic responses

One of the most fundamental problems in immunology is the seemingly schizophrenic ability of the immune system to launch robust immunity against pathogens, while acquiring and maintaining a state of tolerance to the body's own tissues and the trillions of commensal microorganisms and food antigens that confront it every day. A fundamental role for the innate immune system, particularly dendritic cells (DCs), in orchestrating immunological tolerance has been appreciated, but emerging studies have highlighted the nature of the innate receptors and the signaling pathways that program DCs to a tolerogenic state. Furthermore, several studies have emphasized the major role played by cellular interactions and the microenvironment in programming tolerogenic DCs. Here, we review these studies and suggest that the innate control of tolerogenic responses can be viewed as different hierarchies of organization, in which DCs, their innate receptors and signaling networks, and their interactions with other cells and local microenvironments represent different levels of the hierarchy.

Dendritic cells as targets for therapy in rheumatoid arthritis

Dendritic cells (DCs) are central in inducing immunity and in mediating immune tolerance in their role as professional antigen-presenting cells. In the absence of DCs, a fatal autoimmunity develops in animal models. Although the role of DCs has been investigated extensively in the pathogenesis of rheumatoid arthritis (RA), it remains unclear whether DCs initiate autoimmunity in this disease. Nevertheless, evidence points towards a significant role for DCs in disease maintenance and progression. Current biologic therapies target cytokine products of antigen-presenting cells, such as tumor necrosis factor, interleukin-1 and interleukin-6. Emerging therapies for RA exploit the tolerogenic capacity of DCs. 'Tolerogenic' DCs can be generated from myeloid precursors ex vivo, loaded with antigen, and manipulated to suppress autoimmune responses in vivo, through the induction of activation-induced cell death, anergy, and/or regulatory T cells. Cells that are primed by DCs, such as B cells, type 1 and type 17 T helper cells, and that have been implicated in certain models of autoimmunity, are also being considered as additional targets for immune-based therapy. Studies to validate these approaches to ameliorate autoimmunity will be necessary before their application in the clinic.

Role of dendritic cells and alveolar macrophages in regulating early host defense against pulmonary infection with Cryptococcus neoformans

Successful pulmonary clearance of the encapsulated yeast Cryptococcus neoformans requires a T1 adaptive immune response. This response takes up to 3 weeks to fully develop. The role of the initial, innate immune response against the organism is uncertain. In this study, an established model of diphtheria toxin-mediated depletion of resident pulmonary dendritic cells (DC) and alveolar macrophages (AM) was used to assess the contribution of these cells to the initial host response against cryptococcal infection. The results demonstrate that depletion of DC and AM one day prior to infection results in rapid clinical deterioration and death of mice within 6 days postinfection; this effect was not observed in infected groups of control mice not depleted of DC and AM. Depletion did not alter the microbial burden or total leukocyte recruitment in the lung. Mortality (in mice depleted of DC and AM) was associated with increased neutrophil and B-cell accumulation accompanied by histopathologic evidence of suppurative neutrophilic bronchopneumonia, cyst formation, and alveolar damage. Collectively, these data define an important role for DC and AM in regulating the initial innate immune response following pulmonary infection with C. neoformans. These findings provide important insight into the cellular mechanisms which coordinate early host defense against an invasive fungal pathogen in the lung.