Differential capability of human cutaneous dendritic cell subsets to initiate Th17 responses

Dendritic Cell Plasticity in Tumor-Conditioned Skin: CD14(+) Cells at the Cross-Roads of Immune Activation and Suppression

Tumors abuse myeloid plasticity to re-direct dendritic cell (DC) differentiation from T cell stimulatory subsets to immune-suppressive subsets that can interfere with anti-tumor immunity. Lined by a dense network of easily accessible DC the skin is a preferred site for the delivery of DC-targeted vaccines. Various groups have recently been focusing on functional aspects of DC subsets in the skin and how these may be affected by tumor-derived suppressive factors. IL-6, Prostaglandin-E2, and IL-10 were identified as factors in cultures of primary human tumors responsible for the inhibited development and activation of skin DC as well as monocyte-derived DC. IL-10 was found to be uniquely able to convert fully developed DC to immature macrophage-like cells with functional M2 characteristics in a physiologically highly relevant skin explant model in which the phenotypic and functional traits of “crawl-out” DC were studied. Mostly from mouse studies, the JAK2/STAT3 signaling pathway has emerged as a “master switch” of tumor-induced immune suppression. Our lab has additionally identified p38-MAPK as an important signaling element in human DC suppression, and recently validated it as such in ex vivo cultures of single-cell suspensions from melanoma metastases. Through the identification of molecular mechanisms and signaling events that drive myeloid immune suppression in human tumors, more effective DC-targeted cancer vaccines may be designed.

Human dendritic cells - stars in the skin

"A properly functioning adaptive immune system signifies the best features of life. It is diverse beyond compare, tolerant without fail, and capable of behaving appropriately with a myriad of infections and other challenges. Dendritic cells (DCs) are required to explain how this remarkable system is energized and directed." This is a quote by one of the greatest immunologists our community has ever known, and the father of dendritic cells, Ralph Steinman. Steinman's discovery of DCs in 1973 and his subsequent research opened a new field of study within immunology: DC biology and in particular the role of DCs in immune regulation in health and disease. Here, I review themes from our work and others on the complex network of dendritic cells in the skin and discuss the significance of skin DCs in understanding aspects of host defense against infections, the pathology of inflammatory skin diseases, and speculate on the future effective immune-based therapies.

Nerve-derived transmitters including peptides influence cutaneous immunology

Clinical observations suggest that the nervous and immune systems are closely related. For example, inflammatory skin disorders; such as psoriasis, atopic dermatitis, rosacea and acne; are widely believed to be exacerbated by stress. A growing body of research now suggests that neuropeptides and neurotransmitters serve as a link between these two systems. Neuropeptides and neurotransmitters are released by nerves innervating the skin to influence important actors of the immune system, such as Langerhans cells and mast cells, which are located within close anatomic proximity. Catecholamines and other sympathetic transmitters that are released in response to activation of the sympathetic nervous system are also able to reach the skin and affect immune cells. Neuropeptides appear to direct the outcome of Langerhans cell antigen presentation with regard to the subtypes of Th cells generated and neuropeptides induce the degranulation of mast cells, among other effects. Additionally, endothelial cells, which release many inflammatory mediators and express cell surface molecules that allow leukocytes to exit the bloodstream, appear to be regulated by certain neuropeptides and transmitters. This review focuses on the evidence that products of nerves have important regulatory activities on antigen presentation, mast cell function and endothelial cell biology. These activities are highly likely to have clinical and therapeutic relevance.

IL-10 conditioning of human skin affects the distribution of migratory dendritic cell subsets and functional T cell differentiation

In cancer patients pervasive systemic suppression of Dendritic Cell (DC) differentiation and maturation can hinder vaccination efficacy. In this study we have extensively characterized migratory DC subsets from human skin and studied how their migration and T cell-stimulatory abilities were affected by conditioning of the dermal microenvironment through cancer-related suppressive cytokines. To assess effects in the context of a complex tissue structure, we made use of a near-physiological skin explant model. By 4-color flow cytometry, we identified migrated Langerhans Cells (LC) and five dermis-derived DC populations in differential states of maturation. From a panel of known tumor-associated suppressive cytokines, IL-10 showed a unique ability to induce predominant migration of an immature CD14(+)CD141(+)DC-SIGN(+) DC subset with low levels of co-stimulatory molecules, up-regulated expression of the co-inhibitory molecule PD-L1 and the M2-associated macrophage marker CD163. A similarly immature subset composition was observed for DC migrating from explants taken from skin overlying breast tumors. Whereas predominant migration of mature CD1a(+) subsets was associated with release of IL-12p70, efficient Th cell expansion with a Th1 profile, and expansion of functional MART-1-specific CD8(+) T cells, migration of immature CD14(+) DDC was accompanied by increased release of IL-10, poor expansion of CD4(+) and CD8(+) T cells, and skewing of Th responses to favor coordinated FoxP3 and IL-10 expression and regulatory T cell differentiation and outgrowth. Thus, high levels of IL-10 impact the composition of skin-emigrated DC subsets and appear to favor migration of M2-like immature DC with functional qualities conducive to T cell tolerance.

Functional diversity of human vaginal APC subsets in directing T-cell responses

Human vaginal mucosa is the major entry site of sexually transmitted pathogens and thus has long been attractive as a site for mounting mucosal immunity. It is also known as a tolerogenic microenvironment. Here, we demonstrate that immune responses in the vagina can be orchestrated by the functional diversity of four major antigen-presenting cell (APC) subsets. Langerhans cells (LCs) and CD14(-) lamina propria-dendritic cells (LP-DCs) polarize CD4(+) and CD8(+) T cells toward T-helper type 2 (Th2), whereas CD14(+) LP-DCs and macrophages polarize CD4(+) T cells toward Th1. Both LCs and CD14(-) LP-DCs are potent inducers of Th22. Owing to their functional specialties and the different expression levels of pattern-recognition receptors on the APC subsets, microbial products do not bias them to elicit common types of immune responses (Th1 or Th2). To evoke desired types of adaptive immune responses in the human vagina, antigens may need to be targeted to proper APC subsets with right adjuvants.

Signaling through purinergic receptors for ATP induces human cutaneous innate and adaptive Th17 responses: implications in the pathogenesis of psoriasis

Human cutaneous dendritic cells (DCs) have the ability to prime and bias Th17 lymphocytes. However, the factors that stimulate cutaneous DCs to induce Th17 responses are not well known. Alarmins, such as ATP, likely play a pivotal role in the induction and maintenance of cutaneous immune responses by stimulating DC maturation, chemotaxis, and secretion of IL-1β and IL-6, Th17-biasing cytokines. In this study, using a well-established human skin model, we have demonstrated that signaling purinergic receptors, predominantly the P2X7 receptor (P2X7R), via an ATP analog initiate innate proinflammatory inflammation, DC17 differentiation, and the subsequent induction of Th17-biased immunity. Moreover, our results suggest a potential role for P2X7R signaling in the initiation of psoriasis pathogenesis, a Th17-dependent autoimmune disease. In support of this, we observed the increased presence of P2X7R in nonlesional and lesional psoriatic skin compared with normal healthy tissues. Interestingly, there was also a P2X7R variant that was highly expressed in lesional psoriatic skin compared with nonlesional psoriatic and normal healthy skin. Furthermore, we demonstrated that psoriatic responses could be initiated via P2X7R signaling in nonlesional skin following treatment with a P2X7R agonist. Mechanistic studies revealed a P2X7R-dependent mir-21 angiogenesis pathway that leads to the expression of vascular endothelial growth factor and IL-6 and that may be involved in the development of psoriatic lesions. In conclusion, we have established that purinergic signaling in the skin induces innate inflammation, leading to the differentiation of human Th17 responses, which have implications in the pathogenesis and potential treatment of psoriasis.

Differential capacity of human skin dendritic cells to polarize CD4+ T cells into IL-17, IL-21 and IL-22 producing cells

Accumulating evidence suggests a contribution of T cell-derived IL-17, IL-21 and IL-22 cytokines in skin immune homeostasis as well as inflammatory disorders. Here, we analyzed whether the cytokine-producing T lymphocytes could be induced by the different subsets of human skin dendritic cells (DCs), i.e., epidermal Langerhans cells (LCs), dermal CD1c(+)CD14(-) and CD14(+) DCs (DDCs). DCs were purified following a 2-day migration from separated epidermal and dermal sheets and co-cultured with allogeneic T cells before cytokine secretion was explored. Results showed that no skin DCs could induce substantial IL-17 production by naïve CD4(+) or CD8(+)T lymphocytes whereas all of them could induce IL-17 production by memory T cells. In contrast, LCs and CD1c(+)CD14(-)DDCs were able to differentiate naïve CD4(+)T lymphocytes into IL-22 and IL-21-secreting cells, LCs being the most efficient in this process. Intracellular cytokine staining showed that the majority of IL-21 or IL-22 secreting CD4(+)T lymphocytes did not co-synthesized IFN-γ, IL-4 or IL-17. IL-21 and IL-22 production were dependent on the B7/CD28 co-stimulatory pathway and ICOS-L expression on skin LCs significantly reduced IL-21 level. Finally, we found that TGF-β strongly down-regulates both IL-21 and IL-22 secretion by allogeneic CD4(+) T cells. These results add new knowledge on the functional specialization of human skin DCs and might suggest new targets in the treatment of inflammatory skin disorders.

Dendritic cells and vaccine design for sexually-transmitted diseases

Dendritic cells (DCs) are major antigen presenting cells (APCs) that can initiate and control host immune responses toward either immunity or tolerance. These features of DCs, as immune orchestrators, are well characterized by their tissue localizations as well as by their subset-dependent functional specialties and plasticity. Thus, the level of protective immunity to invading microbial pathogens can be dependent on the subsets of DCs taking up microbial antigens and their functional plasticity in response to microbial products, host cellular components and the cytokine milieu in the microenvironment. Vaccines are the most efficient and cost-effective preventive medicine against infectious diseases. However, major challenges still remain for the diseases caused by sexually-transmitted pathogens, including HIV, HPV, HSV and Chlamydia. We surmise that the establishment of protective immunity in the female genital mucosa, the major entry and transfer site of these pathogens, will bring significant benefit for the protection against sexually-transmitted diseases. Recent progresses made in DC biology suggest that vaccines designed to target proper DC subsets may permit us to establish protective immunity in the female genital mucosa against sexually-transmitted pathogens.

The nature of innate and adaptive interleukin-17A responses in sham or bacterial inoculation

Streptococcus pyogenes is the causative agent of numerous diseases ranging from benign infections (pharyngitis and impetigo) to severe infections associated with high mortality (necrotizing fasciitis and bacterial sepsis). As with other bacterial infections, there is considerable interest in characterizing the contribution of interleukin-17A (IL-17A) responses to protective immunity. We here show significant il17a up-regulation by quantitative real-time PCR in secondary lymphoid organs, correlating with increased protein levels in the serum within a short time of S. pyogenes infection. However, our data offer an important caveat to studies of IL-17A responsiveness following antigen inoculation, because enhanced levels of IL-17A were also detected in the serum of sham-infected mice, indicating that inoculation trauma alone can stimulate the production of this cytokine. This highlights the potency and speed of innate IL-17A immune responses after inoculation and the importance of proper and appropriate controls in comparative analysis of immune responses observed during microbial infection.

Transcutaneous vaccination via laser microporation

Driven by constantly increasing knowledge about skin immunology, vaccine delivery via the cutaneous route has recently gained renewed interest. Considering its richness in immunocompetent cells, targeting antigens to the skin is considered to be more effective than intramuscular or subcutaneous injections. However, circumvention of the superficial layer of the skin, the stratum corneum, represents the major challenge for cutaneous immunization. An optimal delivery method has to be effective and reliable, but also highly adaptable to specific demands, should avoid the use of hypodermic needles and the requirement of specially trained healthcare workers. The P.L.E.A.S.E.® (Precise Laser Epidermal System) device employed in this study for creation of aqueous micropores in the skin fulfills these prerequisites by combining the precision of its laser scanning technology with the flexibility to vary the number, density and the depth of the micropores in a user-friendly manner. We investigated the potential of transcutaneous immunization via laser-generated micropores for induction of specific immune responses and compared the outcomes to conventional subcutaneous injection. By targeting different layers of the skin we were able to bias polarization of T cells, which could be modulated by addition of adjuvants. The P.L.E.A.S.E.® device represents a highly effective and versatile platform for transcutaneous vaccination.

Human epidermal Langerhans cells maintain immune homeostasis in skin by activating skin resident regulatory T cells

Recent studies have demonstrated that the skin of a normal adult human contains 10-20 billion resident memory T cells, including various helper, cytotoxic, and regulatory T cell subsets, that are poised to respond to environmental antigens. Using only autologous human tissues, we report that both in vitro and in vivo, resting epidermal Langerhan cells (LCs) selectively and specifically induced the activation and proliferation of skin resident regulatory T (Treg) cells, a minor subset of skin resident memory T cells. In the presence of foreign pathogen, however, the same LCs activated and induced proliferation of effector memory T (Tem) cells and limited Treg cells' activation. These underappreciated properties of LCs, namely maintenance of tolerance in normal skin, and activation of protective skin resident memory T cells upon infectious challenge, help clarify the role of LCs in skin.

Skin-resident murine dendritic cell subsets promote distinct and opposing antigen-specific T helper cell responses

Skin-resident dendritic cells (DCs) are well positioned to encounter cutaneous pathogens and are required for the initiation of adaptive immune responses. There are at least three subsets of skin DC- Langerhans cells (LC), Langerin(+) dermal DCs (dDCs), and classic dDCs. Whether these subsets have distinct or redundant function in vivo is poorly understood. Using a Candida albicans skin infection model, we have shown that direct presentation of antigen by LC is necessary and sufficient for the generation of antigen-specific T helper-17 (Th17) cells but not for the generation of cytotoxic lymphocytes (CTLs). In contrast, Langerin(+) dDCs are required for the generation of antigen specific CTL and Th1 cells. Langerin(+) dDCs also inhibited the ability of LCs and classic DCs to promote Th17 cell responses. This work demonstrates that skin-resident DC subsets promote distinct and opposing antigen-specific responses.

Monocytes differentiated with GM-CSF and IL-15 initiate Th17 and Th1 responses that are contact-dependent and mediated by IL-15

Distinct types of DCs are generated from monocytes using GM-CSF with IL-4 (IL4-DC) or IL-15 (IL15-DC). IL15-DCs are potent inducers of antigen-specific CD8(+) T cells, display a phenotype similar to CD14(+) cells commonly described in chronically inflamed tissues, and produce high levels of IL-1β and IL-15 in response to TLR4 stimulation. As these cytokines promote Th17 responses, which are also associated with inflammatory diseases, I hypothesized that TLR-primed IL15-DCs favor Th17 activation over IL4-DCs. Compared with IL4-DCs, IL15-DCs stimulated with TLR agonists secreted significantly higher concentrations of the Th17-promoting factors, IL-1β, IL-6, IL-23, and CCL20, and lower levels of the Th1 cytokine, IL-12. In addition, IL15-DCs and not IL4-DCs up-regulated IL-15 on the cell surface in response to TLR agonists. IL15-DCs primed with TLR3 or TLR4 agonists triggered Th17 (IL-17, IL-22, and/or IFN-γ) and Th1 (IFN-γ) responses, whereas IL4-DCs primed with the same TLR agonists activated Th1 (IFN-γ) responses. Secretion of IL-17 and IFN-γ required contact with TLR-primed IL15-DC, and IFN-γ production was mediated by membrane-bound IL-15. These findings identify key differences in monocyte-derived DCs, which impact adaptive immunity, and provide primary evidence that IL-15 promotes Th17 and Th1 responses by skewing monocytes into IL15-DC.

Characterization of Langerin-expressing dendritic cell subsets in the normal cornea

PURPOSE

In addition to Langerhans cells (LCs), other dendritic cells (CD11c(+)) have recently been shown to express Langerin (c-type lectin). In skin, (non-LC) Langerin+ dendritic cells initiate adaptive immunity. However, whether such dendritic cells (DC) reside in the cornea, an immune-privileged tissue, is unknown.

METHODS

Normal C57BL/6 corneas were harvested for qRT-PCR analyses of Langerin expression in the epithelium versus stroma. Immunohistochemistry for Langerin was also performed. Single-cell preparations of epithelium versus stroma were FACS analyzed for CD11c, CD11b, and CD103 expression. Fluorescence microscopy of corneas from muLangerin-eGFP mice (in which all CD11c(+) Langerin+ cells express eGFP), huLangerin-DTA mice (only LCs are constitutively deleted), and huLangerin-Cre eYFP-flox (only LCs express eYFP) was performed.

RESULTS

qRT-PCR, immunohistochemistry, and FACS analysis identified CD11c(+) Langerin+ cells in the epithelium and stroma. Similarly, corneas of muLangerin-eGFP mice contained eGFP+ cells in the epithelium and stroma. However, FACS analysis indicated phenotypically differing CD11c(+) Langerin+ populations in the epithelium (CD11b(low)CD103(low)) versus stroma (CD11b(+)CD103(low)). Additionally, corneas from huLangerin-DTA mice were devoid of Langerin+ cells in the epithelium but were detectable in the stroma. In corneas from huLangerin-Cre eYFP-flox, eYFP+ cells were detectable in the epithelium but not in the stroma.

CONCLUSIONS

The normal corneal epithelium is endowed with CD11c(+) Langerin+ cells that are LCs, whereas the stroma is endowed with a separate population of (non-LC) Langerin+ DCs. These findings should henceforth facilitate the examination of Langerin-expressing DC subsets in the immunopathogeneses of conditions such as keratoconjunctivitis sicca, allergic keratoconjunctivitis, and corneal allograft rejection.

Muramyl dipeptide induces Th17 polarization through activation of endothelial cells

Endothelial cells (ECs) express the nucleotide-binding oligomerization domain (Nod) receptor 2, which recognizes the bacterial derivate muramyl dipeptide (MDP). MDP stimulation of these cells enhances their IL-6 production and may thus contribute to the immune and inflammatory activities in the skin. However, whether ECs are capable of influencing the development of T cell priming and its polarization remains unknown. We report that in vitro the murine bEnd.3 EC line induces, following MDP stimulation, a Th17 polarization at the expense of Th1 and Th2 polarization in the setting of Langerhans cell (LC) Ag presentation to responsive T cells as assessed by IL-17, IL-6, IFN-γ, and IL-4 production. Interestingly, IL-22 production, which has been associated with Th17 priming, was not influenced by MDP-treated bEnd.3 cells, illustrating differential regulation of this cytokine from IL-17. Additional analysis confirmed a significantly increased percentage of IL-17(+)CD4(+) T cells by flow cytometry and an increased mRNA level of the specific Th17 transcription factor retinoic acid-related orphan receptor γt in cocultures of LCs and responsive T cells in the presence of activated bEnd.3 cells. Experiments using the RNA interference technique to knockdown IL-6 in bEnd.3 cells confirmed that IL-6 produced by bEnd.3 cells stimulated by MDP is at least partially involved in Th17 polarization. Our data suggest that activated ECs are capable of influencing LC Ag processing and presentation to T cells and induce a Th17 polarization. These results are important for the understanding of Th17-related disorders of the skin such as psoriasis.

The dermis as a portal for dendritic cell-targeted immunotherapy of cutaneous melanoma

Complete surgical excision at an early stage remains the only curative treatment for cutaneous melanoma with few available adjuvant therapy options. Nevertheless, melanoma is a relatively immunogenic tumor type and particularly amenable to immunotherapeutic approaches. A dense network of cutaneous dendritic cells (DC) may account for the reported efficacy of vaccination through the skin and provide an attractive target for the immunotherapy of melanoma. Several phenotypically distinct DC subsets are discernable in the skin, among others, epidermal Langerhans cells and dermal DC. Upon appropriate activation both subsets can efficiently migrate to melanoma-draining lymph nodes (LN) to prime T cell-mediated responses. Unfortunately, from an early stage, melanoma development is characterized by strong immune suppression, facilitating unchecked tumor growth and spread. Particularly the primary tumor site and the first-line tumor-draining LN, the so-called sentinel LN, bear the brunt of this melanoma-induced immune suppression-and these are exactly the sites where anti-melanoma effector T cell responses should be primed by DC in order to prevent early metastasis. Through local immunopotentiation or through DC-targeted vaccination, the dermis may be utilized as a portal to activate DC and kick-start or boost effective T cell-mediated anti-melanoma immunity, even in the face of this immune suppression.

Insight into the immunobiology of human skin and functional specialization of skin dendritic cell subsets to innovate intradermal vaccination design

Dendritic cells (DC) are the key initiators and regulators of any immune response which determine the outcome of CD4(+) and CD8(+) T-cell responses. Multiple distinct DC subsets can be distinguished by location, phenotype, and function in the homeostatic and inflamed human skin. The function of steady-state cutaneous DCs or recruited inflammatory DCs is influenced by the surrounding cellular and extracellular skin microenvironment. The skin is an attractive site for vaccination given the extended local network of DCs and the easy access to the skin-draining lymph nodes to generate effector T cells and immunoglobulin-producing B cells for long-term protective immunity. In the context of intradermal vaccination we describe in this review the skin-associated immune system, the characteristics of the different skin DC subsets, the mechanism of antigen uptake and presentation, and how the properties of DCs can be manipulated. This knowledge is critical for the development of intradermal vaccine strategies and supports the concept of intradermal vaccination as a superior route to the conventional intramuscular or subcutaneous methods.

Differences in T-helper polarizing capability between human monocyte-derived dendritic cells and monocyte-derived Langerhans'-like cells

Langerhans' cells (LCs) represent a specific subset of dendritic cells (DCs) which are important for detecting and processing pathogens that penetrate the skin and epithelial barriers. The aim of our study was to explain what makes their in vitro counterparts - monocyte-derived Langerhans'-like cells (MoLCs) - unique compared with monocyte-derived dendritic cells (MoDCs). Immature MoDCs were generated by incubating peripheral blood monocytes with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4. The addition of transforming growth factor-β (TGF-β) to this cytokine cocktail resulted in the generation of MoLCs. MoLCs showed a lower expression of CD83, CD86, HLA-DR and CCR7 compared with MoDCs, regardless of their maturational status. Both immature and mature MoLCs secreted higher quantities of IL-23 compared with MoDCs and this finding correlated with a higher secretion of IL-17 in co-culture of MoLCs with allogeneic CD4(+) T cells. Mature MoLCs, which produced higher levels of IL-12 and lower levels of IL-10 compared with mature MoDCs, were more potent at inducing interferon-γ (IFN-γ) production by CD4(+) T cells in the co-culture system. In conclusion, the finding that mature MoLCs stimulate stronger T-helper 1 and T-helper 17 immune responses than mature MoDCs, makes them better candidates for use in the preparation of anti-tumour DC vaccines.

Selective accumulation of langerhans-type dendritic cells in small airways of patients with COPD

Background

Dendritic cells (DC) linking innate and adaptive immune responses are present in human lungs, but the characterization of different subsets and their role in COPD pathogenesis remain to be elucidated. The aim of this study is to characterize and quantify pulmonary myeloid DC subsets in small airways of current and ex-smokers with or without COPD.

Methods

Myeloid DC were characterized using flowcytometry on single cell suspensions of digested human lung tissue. Immunohistochemical staining for langerin, BDCA-1, CD1a and DC-SIGN was performed on surgical resection specimens from 85 patients. Expression of factors inducing Langerhans-type DC (LDC) differentiation was evaluated by RT-PCR on total lung RNA.

Results

Two segregated subsets of tissue resident pulmonary myeloid DC were identified in single cell suspensions by flowcytometry: the langerin+ LDC and the DC-SIGN+ interstitial-type DC (intDC). LDC partially expressed the markers CD1a and BDCA-1, which are also present on their known blood precursors. In contrast, intDC did not express langerin, CD1a or BDCA-1, but were more closely related to monocytes.

Quantification of DC in the small airways by immunohistochemistry revealed a higher number of LDC in current smokers without COPD and in COPD patients compared to never smokers and ex-smokers without COPD. Importantly, there was no difference in the number of LDC between current and ex-smoking COPD patients.

In contrast, the number of intDC did not differ between study groups. Interestingly, the number of BDCA-1+ DC was significantly lower in COPD patients compared to never smokers and further decreased with the severity of the disease. In addition, the accumulation of LDC in the small airways significantly correlated with the expression of the LDC inducing differentiation factor activin-A.

Conclusions

Myeloid DC differentiation is altered in small airways of current smokers and COPD patients resulting in a selective accumulation of the LDC subset which correlates with the pulmonary expression of the LDC-inducing differentiation factor activin-A. This study identified the LDC subset as an interesting focus for future research in COPD pathogenesis.

Increased circulating pro-inflammatory cytokines and Th17 lymphocytes in Hashimoto's thyroiditis

CONTEXT

Th17 lymphocytes play an important role in different chronic inflammatory and autoimmune conditions.

AIM

The aim of the study was to explore the status of Th17 cells in patients with autoimmune thyroid diseases (AITD).

DESIGN

We assessed the serum levels and in vitro synthesis of IL-17 and IL-22 and of different cytokines (IL-6, IL-15, and IL-23) involved in the differentiation of Th17 cells in the peripheral blood and thyroid glands of 26 patients with AITD, eight with Graves' disease, and 18 with Hashimoto's thyroiditis (HT) as well as 10 healthy controls.

RESULTS

We found enhanced levels of T cells synthesizing IL-17 and IL-22 in the peripheral blood from AITD patients, mainly in those with HT. In addition, a stronger expression of IL-17 and IL-22 and an enhanced number of IL-23R(+) cells was detected in thyroid glands from HT patients compared with Graves' disease or controls. Furthermore, increased concentrations of IL-6 and IL-15 were detected in sera from HT patients, whereas serum levels of IL-23 tended to be higher in these patients. Finally, an enhanced in vitro differentiation of T lymphocytes into Th17 cells induced by IL-23/IL-6 was observed in AITD patients. Accordingly, a strong induction of RORC2 gene was detected in lymphocytes from HT patients when stimulated with IL-23.

CONCLUSION

Our results indicate that there is an increased differentiation of Th17 lymphocytes and an enhanced synthesis of Th17 cytokines in AITD, mainly in HT. These phenomena may have an important role in the pathogenesis of thyroid autoimmunity.

Neutrophils and macrophages work in concert as inducers and effectors of adaptive immunity against extracellular and intracellular microbial pathogens

Emerging data suggest new facets of the concerted participation of neutrophils and macrophages in antimicrobial immunity. The classical view is that DCs and macrophages are the inducers of adaptive antimicrobial immunity, but there is evidence for neutrophil participation in this task as cytokine and chemokine producers and APCs. On the other hand, the concept that the T(H)1 response is only associated with control of infections by intracellular pathogens through activation of macrophages by IFN-gamma, and the T(H)17/IL-17 axis is only involved in protection against extracellular pathogens through mobilization and activation of neutrophils is simplistic: There is evidence suggesting that T(H)1 and T(H)17 responses, separately or in parallel, may use macrophages and neutrophils against infections by extracellular and intracellular microbial pathogens. Opsonization by pathogen-specific Igs enhances the antimicrobial capabilities of neutrophils and macrophages in infections by extracellular and intracellular microbes. The functional partnership between macrophages and neutrophils as inducers and effectors of adaptive antimicrobial immunity conforms to their affiliation with the myeloid phagocyte system and reveals a strategy based on the concurrent use of the two professional phagocytes in the adaptive defense mechanisms. Starting from a common myeloid precursor in the bone marrow, macrophages and neutrophils split during differentiation but come together at the infectious foci for a cooperative strategy that uses modulator and effector activities to attack invading microbial pathogens.

Human Langerhans cells induce distinct IL-22-producing CD4+ T cells lacking IL-17 production

IL-22 is a cytokine that acts mainly on epithelial cells. In the skin, it mediates keratinocyte proliferation and epidermal hyperplasia and is thought to play a central role in inflammatory diseases with marked epidermal acanthosis, such as psoriasis. Although IL-22 was initially considered a Th17 cytokine, increasing evidence suggests that T helper cells can produce IL-22 even without IL-17 expression. In addition, we have shown the existence of this unique IL-22-producing T cell in normal skin and in the skin of psoriasis and atopic dermatitis patients. In the present study, we investigated the ability of cutaneous resident dendritic cells (DCs) to differentiate IL-22-producing cells. Using FACS, we isolated Langerhans cells (LCs; HLA-DR(+)CD207(+) cells) and dermal DCs (HLA-DR(hi)CD11c(+)BDCA-1(+) cells) from normal human epidermis and dermis, respectively. Both LCs and dermal DCs significantly induced IL-22-producing CD4(+) and CD8(+) T cells from peripheral blood T cells and naive CD4(+) T cells in mixed leukocyte reactions. LCs were more powerful in the induction of IL-22-producing cells than dermal DCs. Moreover, in vitro-generated LC-type DCs induced IL-22-producing cells more efficiently than monocyte-derived DCs. The induced IL-22 production was more correlated with IFN-gamma than IL-17. Surprisingly, the majority of IL-22-producing cells induced by LCs and dermal DCs lacked the expression of IL-17, IFN-gamma, and IL-4. Thus, LCs and dermal DCs preferentially induced helper T cells to produce only IL-22, possibly "Th22" cells. Our data indicate that cutaneous DCs, especially LCs, may control the generation of distinct IL-22 producing Th22 cells infiltrating into the skin.

TLR-stimulated CD34 stem cell-derived human skin-like and monocyte-derived dendritic cells fail to induce Th17 polarization of naive T cells but do stimulate Th1 and Th17 memory responses

Dendritic cells (DCs) are important in linking innate and adaptive immune responses by priming and polarizing naive CD4(+) Th cells, but little is known about the effect of different human DC subsets on Th cells, particularly Th17 cells. We have investigated the ability of TLR-stimulated human Langerhans cells (LC), dermal DCs (dDC), and monocyte-derived DCs (moDC) to affect naive and memory Th17 and Th1 responses. MoDCs stimulated greater memory T cell proliferation while LCs and dDCs more potently stimulated naive T cell proliferation, indicating functionally distinct subsets of DCs. TLR stimulation of all three DC types was unable to induce Th17 polarization from naive T cell precursors, despite inducing Th1 polarization. Dectin stimulation of DCs in IMDM was however able to produce Th17 cells. TLR-stimulated DCs were capable of inducing IL-17A and IFN-gamma production from memory T cells, although the mechanism used by each DC subset differed. MoDCs partially mediated this effect on memory Th1 and Th17 cells by the production of soluble factors, which correlated with their ability to secrete IL-12p70 and IL-23. In contrast, LCs and dDCs were able to elicit a similar memory response to moDCs, but in a contact dependent manner. Additionally, the influence of microbial stimulation was demonstrated with TLR3 and TLR7/8 agonists inducing a Th1 response, whereas TLR2 or dectin stimulation of moDCs enhanced the IL-17 response. This study emphasizes the differences between human DC subsets and demonstrates that both the DC subset and the microbial stimulus influence the Th cell response.