"Dermal dendritic cells" comprise two distinct populations: CD1+ dendritic cells and CD209+ macrophages

Extracellular Matrix-Bioinspired Anisotropic Topographical Cues of Electrospun Nanofibers: A Strategy of Wound Healing through Macrophage Polarization

The skin serves as the body's outermost barrier and is the largest organ, providing protection not only to the body but also to various internal organs. Owing to continuous exposure to various external factors, it is susceptible to damage that can range from simple to severe, including serious types of wounds such as burns or chronic wounds. Macrophages play a crucial role in the entire wound-healing process and contribute significantly to skin regeneration. Initially, M1 macrophages infiltrate to phagocytose bacteria, debris, and dead cells in fresh wounds. As tissue repair is activated, M2 macrophages are promoted, reducing inflammation and facilitating restoration of the dermis and epidermis to regenerate the tissue. This suggests that extracellular matrix (ECM) promotes cell adhesion, proliferation, migrationand macrophage polarization. Among the numerous strategies, electrospinning is a versatile technique for obtaining ECM-mimicking structures with anisotropic and isotropic topologies of micro/nanofibers. Various electrospun biomaterials influence macrophage polarization based on their isotropic or anisotropic topologies. Moreover, these fibers possess a high surface-area-to-volume ratio, promoting the effective exchange of vital nutrients and oxygen, which are crucial for cell viability and tissue regeneration. Micro/nanofibers with diverse physical and chemical properties can be tailored to polarize macrophages toward skin regeneration and wound healing, depending on specific requirements. This review describes the significance of micro/nanostructures for activating macrophages and promoting wound healing.

Tissue adaptation of CD4 T lymphocytes in homeostasis and cancer

The immune system is traditionally classified as a defense system that can discriminate between self and non-self or dangerous and non-dangerous situations, unleashing a tolerogenic reaction or immune response. These activities are mainly coordinated by the interaction between innate and adaptive cells that act together to eliminate harmful stimuli and keep tissue healthy. However, healthy tissue is not always the end point of an immune response. Much evidence has been accumulated over the years, showing that the immune system has complex, diversified, and integrated functions that converge to maintaining tissue homeostasis, even in the absence of aggression, interacting with the tissue cells and allowing the functional maintenance of that tissue. One of the main cells known for their function in helping the immune response through the production of cytokines is CD4+ T lymphocytes. The cytokines produced by the different subtypes act not only on immune cells but also on tissue cells. Considering that tissues have specific mediators in their architecture, it is plausible that the presence and frequency of CD4+ T lymphocytes of specific subtypes (Th1, Th2, Th17, and others) maintain tissue homeostasis. In situations where homeostasis is disrupted, such as infections, allergies, inflammatory processes, and cancer, local CD4+ T lymphocytes respond to this disruption and, as in the healthy tissue, towards the equilibrium of tissue dynamics. CD4+ T lymphocytes can be manipulated by tumor cells to promote tumor development and metastasis, making them a prognostic factor in various types of cancer. Therefore, understanding the function of tissue-specific CD4+ T lymphocytes is essential in developing new strategies for treating tissue-specific diseases, as occurs in cancer. In this context, this article reviews the evidence for this hypothesis regarding the phenotypes and functions of CD4+ T lymphocytes and compares their contribution to maintaining tissue homeostasis in different organs in a steady state and during tumor progression.

Large-scale functional inference for skin-expressing lncRNAs using expression and sequence information

Long noncoding RNAs (lncRNAs) regulate the expression of protein-coding genes and have been shown to play important roles in inflammatory skin diseases. However, we still have limited understanding of the functional impact of lncRNAs in skin, partly due to their tissue specificity and lower expression levels compared with protein-coding genes. We compiled a comprehensive list of 18,517 lncRNAs from different sources and studied their expression profiles in 834 RNA-Seq samples from multiple inflammatory skin conditions and cytokine-stimulated keratinocytes. Applying a balanced random forest to predict involvement in biological functions, we achieved a median AUROC of 0.79 in 10-fold cross-validation, identifying significant DNA binding domains (DBDs) for 39 lncRNAs. G18244, a skin-expressing lncRNA predicted for IL-4/IL-13 signaling in keratinocytes, was highly correlated in expression with F13A1, a protein-coding gene involved in macrophage regulation, and we further identified a significant DBD in F13A1 for G18244. Reflecting clinical implications, AC090198.1 (predicted for IL-17 pathway) and AC005332.6 (predicted for IFN-γ pathway) had significant negative correlation with the SCORAD metric for atopic dermatitis. We also utilized single-cell RNA and spatial sequencing data to validate cell type specificity. Our research demonstrates lncRNAs have important immunological roles and can help prioritize their impact on inflammatory skin diseases.

A human 3D immune competent full-thickness skin model mimicking dermal dendritic cell activation

We have integrated dermal dendritic cell surrogates originally generated from the cell line THP-1 as central mediators of the immune reaction in a human full-thickness skin model. Accordingly, sensitizer treatment of THP-1-derived CD14-, CD11c+ immature dendritic cells (iDCs) resulted in the phosphorylation of p38 MAPK in the presence of 1-chloro-2,4-dinitrobenzene (DNCB) (2.6-fold) as well as in degradation of the inhibitor protein kappa B alpha (IκBα) upon incubation with NiSO4 (1.6-fold). Furthermore, NiSO4 led to an increase in mRNA levels of IL-6 (2.4-fold), TNF-α (2-fold) and of IL-8 (15-fold). These results were confirmed on the protein level, with even stronger effects on cytokine release in the presence of NiSO4: Cytokine secretion was significantly increased for IL-8 (147-fold), IL-6 (11.8-fold) and IL-1β (28.8-fold). Notably, DNCB treatment revealed an increase for IL-8 (28.6-fold) and IL-1β (5.6-fold). Importantly, NiSO4 treatment of isolated iDCs as well as of iDCs integrated as dermal dendritic cell surrogates into our full-thickness skin model (SM) induced the upregulation of the adhesion molecule clusters of differentiation (CD)54 (iDCs: 1.2-fold; SM: 1.3-fold) and the co-stimulatory molecule and DC maturation marker CD86 (iDCs ~1.4-fold; SM:~1.5-fold) surface marker expression. Noteworthy, the expression of CD54 and CD86 could be suppressed by dexamethasone treatment on isolated iDCs (CD54: 1.3-fold; CD86: 2.1-fold) as well as on the tissue-integrated iDCs (CD54: 1.4-fold; CD86: 1.6-fold). In conclusion, we were able to integrate THP-1-derived iDCs as functional dermal dendritic cell surrogates allowing the qualitative identification of potential sensitizers on the one hand, and drug candidates that potentially suppress sensitization on the other hand in a 3D human skin model corresponding to the 3R principles ("replace", "reduce" and "refine").

Macrophages CD163+ and Factor XIIIa+ Provide a First-Line Defence against Proliferative Verrucous Leukoplakia Antigens

This study aimed to evaluate the density of the dendritic cells (DCs) and macrophages in oral leukoplakia (OL) and proliferative verrucous leukoplakia (PVL) by immunohistochemical analysis. We analysed paraffined tissue samples of PVL (n = 27), OL (n = 20), and inflammatory fibrous hyperplasia (n = 20) as the control group using the immunomarkers for DCs (CD1a, CD207, CD83, CD208 and CD123) and macrophages (CD68, CD163, FXIIIa and CD209). A quantitative analysis of positive cells in the epithelial and subepithelial areas was determined. Our results showed a reduction in CD208+ cells in the subepithelial area of the OL and PVL compared to the control. Additionally, we found a higher density of FXIIIa+ and CD163+ cells in the subepithelial area in PVL compared to the OL and control. Four-way MANOVA revealed a relationship between increased CD123+ cell density in the subepithelial area of “high-risk” samples regardless of disease. Macrophages provide the first line of defence against PVL antigens, suggesting a distinct pattern of innate immune system activation in PVL compared to OL, which may contribute to the complexity and the high rate of malignant transformation in the PVL.

Subunit vaccines for Acinetobacter baumannii

Acinetobacter baumannii is a gram-negative bacterium and a crucial opportunistic pathogen in hospitals. A. baumannii infection has become a challenging problem in clinical practice due to the increasing number of multidrug-resistant strains and their prevalence worldwide. Vaccines are effective tools to prevent and control A. baumannii infection. Many researchers are studying subunit vaccines against A. baumannii. Subunit vaccines have the advantages of high purity, safety, and stability, ease of production, and highly targeted induced immune responses. To date, no A. baumannii subunit vaccine candidate has entered clinical trials. This may be related to the easy degradation of subunit vaccines in vivo and weak immunogenicity. Using adjuvants or delivery vehicles to prepare subunit vaccines can slow down degradation and improve immunogenicity. The common immunization routes include intramuscular injection, subcutaneous injection, intraperitoneal injection and mucosal vaccination. The appropriate immunization method can also enhance the immune effect of subunit vaccines. Therefore, selecting an appropriate adjuvant and immunization method is essential for subunit vaccine research. This review summarizes the past exploration of A. baumannii subunit vaccines, hoping to guide current and future research on these vaccines.

Adult onset xanthogranuloma of the eyelid

Purpose

To report a rare case of an eyelid lesion in an adult, with histological features of juvenile xanthogranuloma (JXG).

Observations

Juvenile xanthogranuloma primarily affects the skin of infants and young children. It infrequently can involve the structures of the eye and orbit and rarely occurs in individuals beyond the second decade of life. We present a case of adult onset xanthogranuloma (AXG) involving the eyelid of a 29-year-old female. This lesion required management with multiple treatment modalities.

Conclusions

This is a rare example of an eyelid xanthogranuloma in an adult. As such, JXG-like lesions should be included as a differential diagnosis for lesions of the eye and orbit in adults. Surgical management may be required if there is no response to intralesional steroids.

Carbohydrates from Pseudomonas aeruginosa biofilms interact with immune C-type lectins and interfere with their receptor function

Bacterial biofilms represent a challenge to the healthcare system because of their resilience against antimicrobials and immune attack. Biofilms consist of bacterial aggregates embedded in an extracellular polymeric substance (EPS) composed of polysaccharides, nucleic acids and proteins. We hypothesised that carbohydrates could contribute to immune recognition of Pseudomonas aeruginosa biofilms by engaging C-type lectins. Here we show binding of Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN, CD209), mannose receptor (MR, CD206) and Dectin-2 to P. aeruginosa biofilms. We also demonstrate that DC-SIGN, unlike MR and Dectin-2, recognises planktonic P. aeruginosa cultures and this interaction depends on the presence of the common polysaccharide antigen. Within biofilms DC-SIGN, Dectin-2 and MR ligands appear as discrete clusters with dispersed DC-SIGN ligands also found among bacterial aggregates. DC-SIGN, MR and Dectin-2 bind to carbohydrates purified from P. aeruginosa biofilms, particularly the high molecular weight fraction (HMW; >132,000 Da), with K_Ds in the nM range. These HMW carbohydrates contain 74.9–80.9% mannose, display α-mannan segments, interfere with the endocytic activity of cell-associated DC-SIGN and MR and inhibit Dectin-2-mediated cellular activation. In addition, biofilm carbohydrates reduce the association of the DC-SIGN ligand Lewis^x, but not fucose, to human monocyte-derived dendritic cells (moDCs), and alter moDC morphology without affecting early cytokine production in response to lipopolysaccharide or P. aeruginosa cultures. This work identifies the presence of ligands for three important C-type lectins within P. aeruginosa biofilm structures and purified biofilm carbohydrates and highlights the potential for these receptors to impact immunity to P. aeruginosa infection.

In silico Prediction of Skin Sensitization: Quo vadis?

Skin direct contact with chemical or physical substances is predisposed to allergic contact dermatitis (ACD), producing various allergic reactions, namely rash, blister, or itchy, in the contacted skin area. ACD can be triggered by various extremely complicated adverse outcome pathways (AOPs) remains to be causal for biosafety warrant. As such, commercial products such as ointments or cosmetics can fulfill the topically safe requirements in animal and non-animal models including allergy. Europe, nevertheless, has banned animal tests for the safety evaluations of cosmetic ingredients since 2013, followed by other countries. A variety of non-animal in vitro tests addressing different key events of the AOP, the direct peptide reactivity assay (DPRA), KeratinoSens™, LuSens and human cell line activation test h-CLAT and U-SENS™ have been developed and were adopted in OECD test guideline to identify the skin sensitizers. Other methods, such as the SENS-IS are not yet fully validated and regulatorily accepted. A broad spectrum of in silico models, alternatively, to predict skin sensitization have emerged based on various animal and non-animal data using assorted modeling schemes. In this article, we extensively summarize a number of skin sensitization predictive models that can be used in the biopharmaceutics and cosmeceuticals industries as well as their future perspectives, and the underlined challenges are also discussed.

Distribution of CD1a-positive cells is not different between pseudolymphomatous folliculitis and primary cutaneous marginal zone lymphoma

Pseudolymphomatous folliculitis (PLF) is a subtype of cutaneous pseudolymphoma that is recognized as an independent disease. PLF is characterized by dermal lymphocytic infiltration surrounding an irregular hyperplastic pilosebaceous unit (i.e., activated pilosebaceous unit). An interstitial distribution of CD1a-positive cells is regarded as an important feature of PLF, especially in distinguishing it from primary cutaneous marginal zone lymphoma (PCMZL), which is associated with a peripheral concentration of CD1a-positive cells. We undertook a clinicopathological investigation of PLF, with a reassessment of CD1a immunohistochemistry. We defined diagnostic criteria for PLF based on past studies and consequently identified 79 cases. In addition, we collected 32 cases of PCMZL and performed detailed clinical, pathological, and immunohistochemical investigations using antibodies to CD3, CD20, and CD1a. We found an interstitial concentration of CD1a-positive cells in 90.2% of PLF and 34.5% of PCMZL cases. The peripheral concentration of CD1a-positive cells was seen in 9.8% of PLF and 34.5% of PCMZL cases. In both diseases, CD1a-positive cells appeared in T-cell nests (88.5% in PLF and 92.9% in PCMZL) but were absent in B-cell nests (0% in both groups). All 79 cases of PLF showed activated pilosebaceous units while 22 of the 32 PCMZL cases displayed pilosebaceous units, although none of these were activated. In summary, regarding the distribution patterns of CD1a-positive cells as a diagnostic feature in distinguishing between PLF and PCMZL is somewhat inconclusive. To differentiate PLF and PCMZL, determining the presence or absence of activated pilosebaceous units is essential.

Dendritic Cells Currently under the Spotlight; Classification and Subset Based upon New Markers

Dendritic cells (DCs) are considered as a subset of mononuclear phagocytes that composed of multiple subsets with distinct phenotypic features. DCs play crucial roles in the initiation and modulation of immune responses to both allo- and auto-antigens during pathogenic settings, encompassing infectious diseases, cancer, autoimmunity, transplantation, as well as vaccination. DCs play a role in preventing autoimmunity via inducing tolerance to self-antigens. This review focus on the most common subsets of DCs in human. Owing to the low frequencies of DC cells in blood and tissues and also the lack of specific DC markers, studies of DCs have been greatly hindered. Human DCs arise by a dedicated pathway of lympho-myeloid hematopoiesis and give rise into specialized subtypes under the influence of transcription factors that are specific for each linage. In humans, the classification of DCs has been generally separated into the blood and cutaneous subsets, mainly because these parts are more comfortable to examine in humans.

Innate Molecular and Cellular Signature in the Skin Preceding Long-Lasting T Cell Responses after Electroporated DNA Vaccination

DNA vaccines delivered with electroporation (EP) have shown promising results in preclinical models and are evaluated in clinical trials. In this study, we aim to characterize early mechanisms occurring in the skin after intradermal injection and EP of the auxoGTUmultiSIV DNA vaccine in nonhuman primates. First, we show that EP acts as an adjuvant by enhancing local inflammation, notably via granulocytes, monocytes/macrophages, and CD1a^int-expressing cell recruitment. EP also induced Langerhans cell maturation, illustrated by CD86, CD83, and HLA-DR upregulation and their migration out of the epidermis. Second, we demonstrate the crucial role of the DNA vaccine in soluble factors release, such as MCP-1 or IL-15. Transcriptomic analysis showed that EP played a major role in gene expression changes postvaccination. However, the DNA vaccine is required to strongly upregulate several genes involved in inflammatory responses (e.g., Saa4), cell migration (e.g., Ccl3, Ccl5, or Cxcl10), APC activation (e.g., Cd86), and IFN-inducible genes (e.g., Ifit3, Ifit5, Irf7, Isg15, orMx1), illustrating an antiviral response signature. Also, AIM-2, a cytosolic DNA sensor, appeared to be strongly upregulated only in the presence of the DNA vaccine and trends to positively correlate with several IFN-inducible genes, suggesting the potential role of AIM-2 in vaccine sensing and the subsequent innate response activation leading to strong adaptive T cell responses. Overall, these results demonstrate that a combined stimulation of the immune response, in which EP and the auxoGTUmultiSIV vaccine triggered different components of the innate immunity, led to strong and persistent cellular recall responses.

Dendritic Cells in Anticancer Vaccination: Rationale for Ex Vivo Loading or In Vivo Targeting

Dendritic cells (DCs) have shown great potential as a component or target in the landscape of cancer immunotherapy. Different in vivo and ex vivo strategies of DC vaccine generation with different outcomes have been proposed. Numerous clinical trials have demonstrated their efficacy and safety in cancer patients. However, there is no consensus regarding which DC-based vaccine generation method is preferable. A problem of result comparison between trials in which different DC-loading or -targeting approaches have been applied remains. The employment of different DC generation and maturation methods, antigens and administration routes from trial to trial also limits the objective comparison of DC vaccines. In the present review, we discuss different methods of DC vaccine generation. We conclude that standardized trial designs, treatment settings and outcome assessment criteria will help to determine which DC vaccine generation approach should be applied in certain cancer cases. This will result in a reduction in alternatives in the selection of preferable DC-based vaccine tactics in patient. Moreover, it has become clear that the application of a DC vaccine alone is not sufficient and combination immunotherapy with recent advances, such as immune checkpoint inhibitors, should be employed to achieve a better clinical response and outcome.

Melanogenic Properties and Expression Profiles of Melanogenic Paracrine Molecules in Riehl's Melanosis

Riehl's melanosis is a hyperpigmentary disorder that occurs predominantly on the face and neck. To date, the pathogenesis of Riehl's melanosis with regards to the melanogenic properties and paracrine melanogenic molecules has not well been studied. This study was aimed to provide a novel perspective on the pathogenesis of Riehl's melanosis by identifying the relevant paracrine melanogenic molecules in Riehl's melanosis. Skin biopsies were performed on lesional and normal-appearing perilesional skin of 12 patients with Riehl's melanosis and 12 age- and sex-matched healthy controls. Histopathological and immunohistochemical staining for paracrine melanogenic molecules was analyzed. The major histopathological findings of Riehl's melanosis were basal hyperpigmentation, melanocyte proliferation, interface change, dermal pigmentary incontinence, vascular proliferation, and dermal inflammation. Dermal expression intensities of stem cell factor (SCF) and c-kit were increased in the lesional skin of Riehl's melanosis. In addition, increased expression of epidermal and dermal ET-1 was also observed in the lesional skin of Riehl's melanosis. Increased tissue expressions of SCF, c-kit, and ET-1 in Riehl's melanosis support the role of these paracrine melanogenic molecules in the pathogenesis of Riehl's melanosis. The findings from this study might present useful information on the pathogenetic mechanism of Riehl's melanosis.

Tissue-resident macrophages can be generated de novo in adult human skin from resident progenitor cells during substance P-mediated neurogenic inflammation ex vivo

Besides monocyte (MO)-derived macrophages (MACs), self-renewing tissue-resident macrophages (trMACs) maintain the intracutaneous MAC pool in murine skin. Here, we have asked whether the same phenomenon occurs in human skin using organ-cultured, full-thickness skin detached from blood circulation and bone marrow. Skin stimulation ex vivo with the neuropeptide substance P (SP), mimicking neurogenic skin inflammation, significantly increased the number of CD68⁺MACs in the papillary dermis without altering intracutaneous MAC proliferation or apoptosis. Since intraluminal CD14⁺MOs were undetectable in the non-perfused dermal vasculature, new MACs must have differentiated from resident intracutaneous progenitor cells in human skin. Interestingly, CD68⁺MACs were often seen in direct cell-cell-contact with cells expressing both, the hematopoietic stem cell marker CD34 and SP receptor (neurokinin-1 receptor [NK1R]). These cell-cell contacts and CD34⁺cell proliferation were up-regulated in SP-treated skin samples. Collectively, our study provides the first evidence that resident MAC progenitors, from which mature MACs can rapidly differentiate within the tissue, do exist in normal adult human skin. That these NK1R⁺trMAC-progenitor cells quickly respond to a key stress-associated neuroinflammatory stimulus suggests that this may satisfy increased local MAC demand under conditions of wounding/stress.

Identification of Heparan-Sulfate Rich Cells in the Loose Connective Tissues of the Axolotl (Ambystoma mexicanum) with the Potential to Mediate Growth Factor Signaling during Regeneration

Limb regeneration is the outcome of a complex sequence of events that are mediated by interactions between cells derived from the tissues of the amputated stump. Early in regeneration, these interactions are mediated by growth factor/morphogen signaling associated with nerves and the wound epithelium. One shared property of these proregenerative signaling molecules is that their activity is dependent on interactions with sulfated glycosaminoglycans (GAGs), heparan sulfate proteoglycan (HSPG) in particular, in the extracellular matrix (ECM). We hypothesized that there are cells in the axolotl that synthesize specific HSPGs that control growth factor signaling in time and space. In this study we have identified a subpopulation of cells within the ECM of axolotl skin that express high levels of sulfated GAGs on their cell surface. These cells are dispersed in a grid-like pattern throughout the dermis as well as the loose connective tissues that surround the tissues of the limb. These cells alter their morphology during regeneration, and are candidates for being a subpopulation of connective tissue cells that function as the cells required for pattern-formation during regeneration. Given their high level of HSPG expression, their stellate morphology, and their distribution throughout the loose connective tissues, we refer to these as the positional information GRID (Groups that are Regenerative, Interspersed and Dendritic) cells. In addition, we have identified cells that stain for high levels of expression of sulfated GAGs in mouse limb connective tissue that could have an equivalent function to GRID cells in the axolotl. The identification of GRID cells may have important implications for work in the area of Regenerative Engineering.

Airway Macrophage and Dendritic Cell Subsets in the Resting Human Lung

Dendritic cells (DCs) and macrophages (MΦs) are antigen-presenting phagocytic cells found in many peripheral tissues of the human body, including the blood, lymph nodes, skin, and lung. They are vital to maintaining steady-state respiration in the human lung based on their ability to clear airways while also directing tolerogenic or inflammatory responses based on specific stimuli. Over the past three decades, studies have determined that there are multiple subsets of these two general cell types that exist in the airways and interstitium. Identifying these numerous subsets has proven challenging, especially with the unique microenvironments present in the lung. Cells found in the vasculature are not the same subsets found in the skin or the lung, as demonstrated by surface marker expression. By transcriptional profiling, these subsets show similarities but also major differences. Primary human lung cells and/ or tissues are difficult to acquire, particularly in a healthy condition. Additionally, surface marker screening and transcriptional profiling are continually identifying new DC and MΦ subsets. While the overall field is moving forward, we emphasize that more attention needs to focus on replicating the steady-state microenvironment of the lung to reveal the physiological functions of these subsets.

Autophagy links antimicrobial activity with antigen presentation in Langerhans cells

DC, through the uptake, processing, and presentation of antigen, are responsible for activation of T cell responses to defend the host against infection, yet it is not known if they can directly kill invading bacteria. Here, we studied in human leprosy, how Langerhans cells (LC), specialized DC, contribute to host defense against bacterial infection. IFN-γ treatment of LC isolated from human epidermis and infected with Mycobacterium leprae (M. leprae) activated an antimicrobial activity, which was dependent on the upregulation of the antimicrobial peptide cathelicidin and induction of autophagy. IFN-γ induction of autophagy promoted fusion of phagosomes containing M. leprae with lysosomes and the delivery of cathelicidin to the intracellular compartment containing the pathogen. Autophagy enhanced the ability of M. leprae-infected LC to present antigen to CD1a-restricted T cells. The frequency of IFN-γ labeling and LC containing both cathelicidin and autophagic vesicles was greater in the self-healing lesions vs. progressive lesions, thus correlating with the effectiveness of host defense against the pathogen. These data indicate that autophagy links the ability of DC to kill and degrade an invading pathogen, ensuring cell survival from the infection while facilitating presentation of microbial antigens to resident T cells.

HIV-1 vaccination by needle-free oral injection induces strong mucosal immunity and protects against SHIV challenge

The oral mucosa is an attractive site for mucosal vaccination, however the thick squamous epithelium limits antigen uptake. Here we utilize a modified needle-free injector to deliver immunizations to the sublingual and buccal (SL/B) tissue of rhesus macaques. Needle-free SL/B vaccination with modified vaccinia Ankara (MVA) and a recombinant trimeric gp120 protein generates strong vaccine-specific IgG responses in serum as well as vaginal, rectal and salivary secretions. Vaccine-induced IgG responses show a remarkable breadth against gp70-V1V2 sequences from multiple clades of HIV-1. In contrast, topical SL/B immunizations generates minimal IgG responses. Following six intrarectal pathogenic SHIV-SF162P3 challenges, needle-free but not topical immunization results in a significant delay of acquisition of infection. Delay of infection correlates with non-neutralizing antibody effector function, Env-specific CD4+ T-cell responses, and gp120 V2 loop specific antibodies. These results demonstrate needle-free MVA/gp120 oral vaccination as a practical and effective route to induce protective immunity against HIV-1.

In vivo multiphoton microscopy of melasma

Melasma is a skin disorder characterized by hyperpigmented patches due to increased melanin production and deposition. In this pilot study, we evaluate the potential of multiphoton microscopy (MPM) to characterize non-invasively the melanin content, location, and distribution in melasma and assess the elastosis severity. We employed a clinical MPM tomograph to image in vivo morphological features in melasma lesions and adjacent normal skin in 12 patients. We imaged dermal melanophages in most dermal melasma lesions and occasionally in epidermal melasma. The melanin volume fraction values measured in epidermal melasma (14% ± 4%) were significantly higher (p < 0.05) than the values measured in perilesional skin (11% ± 3%). The basal keratinocytes of melasma and perilesions showed different melanin distribution. Elastosis was predominantly more severe in lesions than in perilesions and was associated with changes in melanin distribution of the basal keratinocytes. These results demonstrate that MPM may be a non-invasive imaging tool for characterizing melasma.

Innate Immune Responses in Leprosy

Leprosy is an infectious disease that may present different clinical forms depending on host immune response to Mycobacterium leprae. Several studies have clarified the role of various T cell populations in leprosy; however, recent evidences suggest that local innate immune mechanisms are key determinants in driving the disease to its different clinical manifestations. Leprosy is an ideal model to study the immunoregulatory role of innate immune molecules and its interaction with nervous system, which can affect homeostasis and contribute to the development of inflammatory episodes during the course of the disease. Macrophages, dendritic cells, neutrophils, and keratinocytes are the major cell populations studied and the comprehension of the complex networking created by cytokine release, lipid and iron metabolism, as well as antimicrobial effector pathways might provide data that will help in the development of new strategies for leprosy management.

Tissue Damage Caused by Myeloablative, but Not Non-Myeloablative, Conditioning before Allogeneic Stem Cell Transplantation Results in Dermal Macrophage Recruitment without Active T-Cell Interaction

Introduction

Conditioning regimens preceding allogeneic stem cell transplantation (alloSCT) can cause tissue damage and acceleration of the development of graft-versus-host disease (GVHD). T-cell-depleted alloSCT with postponed donor lymphocyte infusion (DLI) may reduce GVHD, because tissue injury can be restored at the time of DLI. In this study, we investigated the presence of tissue injury and inflammation in skin during the period of hematologic recovery and immune reconstitution after alloSCT.

Methods

Skin biopsies were immunohistochemically stained for HLA class II, CD1a, CD11c, CD40, CD54, CD68, CD86, CD206, CD3, and CD8. HLA class II-expressing cells were characterized as activated T-cells, antigen-presenting cells (APCs), or tissue repairing macrophages. In sex-mismatched patient and donor couples, origin of cells was determined by multiplex analysis combining XY-FISH and fluorescent immunohistochemistry.

Results

No inflammatory environment due to pretransplant conditioning was detected at the time of alloSCT, irrespective of the conditioning regimen. An increase in HLA class II-positive macrophages and CD3 T-cells was observed 12–24 weeks after myeloablative alloSCT, but these macrophages did not show signs of interaction with the co-localized T-cells. In contrast, during GVHD, an increase in HLA class II-expressing cells coinciding with T-cell interaction was observed, resulting in an overt inflammatory reaction with the presence of activated APC, activated donor T-cells, and localized upregulation of HLA class II expression on epidermal cells. In the absence of GVHD, patient derived macrophages were gradually replaced by donor-derived macrophages although patient-derived macrophages were detectable even 24 weeks after alloSCT.

Conclusion

Conditioning regimens cause tissue damage in the skin, but this does not result in a local increase of activated APC. In contrast to the inflamed situation in GVHD, when interaction takes place between activated APC and donor T-cells, the tissue damage caused by myeloablative alloSCT results in dermal recruitment of HLA class II-positive tissue repairing macrophages co-existing with increased numbers of patient- and donor-derived T-cells, but without signs of specific interaction and initiation of an immune response. Thus, the local skin damage caused by the conditioning regimen appears to be insufficient as single factor to provoke GVHD induction.

Application of proteomics in the elucidation of chemical-mediated allergic contact dermatitis

Allergic contact dermatitis (ACD) is a widespread hypersensitivity reaction of the skin. The cellular mechanisms underlying its development are complex and involve close interaction of different cell types of the immune system. It is this very complexity which has long prevented straightforward replacement of the corresponding regulatory in vivo tests. Recent efforts have already resulted in the development of several in vitro testing alternatives that address key steps of ACD. Yet identification of suitable biomarkers is still a subject of intense research. Search strategies for the latter encompass transcriptomics, proteomics as well as metabolomics approaches. The scope of this review shall be the application and use of proteomics in the context of ACD. This includes highlighting relevant aspects of the molecular and cellular mechanisms underlying ACD, the exploitation of these mechanisms for testing and biomarkers (e.g., in the context of the OECD's adverse outcome pathway initiative) as well as an outlook on emerging proteome targets, for example during the allergen-induced activation of dendritic cells (DCs).

Protein-Protein Interaction between Surfactant Protein D and DC-SIGN via C-Type Lectin Domain Can Suppress HIV-1 Transfer

Surfactant protein D (SP-D) is a soluble C-type lectin, belonging to the collectin (collagen-containing calcium-dependent lectin) family, which acts as an innate immune pattern recognition molecule in the lungs at other mucosal surfaces. Immune regulation and surfactant homeostasis are salient functions of SP-D. SP-D can bind to a range of viral, bacterial, and fungal pathogens and trigger clearance mechanisms. SP-D binds to gp120, the envelope protein expressed on HIV-1, through its C-type lectin or carbohydrate recognition domain. This is of importance since SP-D is secreted by human mucosal epithelial cells and is present in the female reproductive tract, including vagina. Another C-type lectin, dendritic cell (DC)-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), present on the surface of the DCs, also binds to HIV-1 gp120 and facilitates viral transfer to the lymphoid tissues. DCs are also present at the site of HIV-1 entry, embedded in vaginal or rectal mucosa. In the present study, we report a direct protein-protein interaction between recombinant forms of SP-D (rfhSP-D) and DC-SIGN via their C-type lectin domains. Both SP-D and DC-SIGN competed for binding to immobilized HIV-1 gp120. Pre-incubation of human embryonic kidney cells expressing surface DC-SIGN with rfhSP-D significantly inhibited the HIV-1 transfer to activated peripheral blood mononuclear cells. In silico analysis revealed that SP-D and gp120 may occupy same sites on DC-SIGN, which may explain the reduced transfer of HIV-1. In summary, we demonstrate, for the first time, that DC-SIGN is a novel binding partner of SP-D, and this interaction can modulate HIV-1 capture and transfer to CD4⁺ T cells. In addition, the present study also reveals a novel and distinct mechanism of host defense by SP-D against HIV-1.

Glycation stimulates cutaneous monocyte differentiation in reconstructed skin in vitro

Glycation reaction is a recognized mechanism related to chronological aging. Previous investigations in cutaneous biology have considered the effect of glycation on the dermal matrix molecules, involved in tissue stiffening during skin aging. However, little is known about a possible direct effect of glycation upon cell differentiation. To address such issue, the effect of glycation has been re-investigated in a reconstructed skin model integrating monocytes that are cells capable of differentiating according to different pathways. The results showed that, in the absence of glycation, a small number of these CD45⁺ cells could differentiate either into dendritic-like cells (DC-SIGN⁺, BDC1a⁺, DC-LAMP⁺) or macrophage- like cells (CD14⁺, CD68⁺, CD163⁺) whereas, with glycation, the number of monocytes, dendritic cells, macrophage-like cells were found surprisingly increased. In-vivo our results showed also that dendritic and macrophage-like cells were increased and suggest a possible link with the age-dependent glycation level in the skin. In addition, we found that, unlike fibroblasts incorporated in the reconstructed skin, these cells expressed specific receptors for AGEs (RAGE and SRA). Taken altogether, our data show that cells of the monocyte lineage, in the presence of AGEs, can differentiate into dendritic or macrophage-like cells and could lead to a micro inflammatory environment.

Immune and biochemical responses in skin differ between bovine hosts genetically susceptible and resistant to the cattle tick Rhipicephalus microplus

Background

Ticks attach to and penetrate their hosts’ skin and inactivate multiple components of host responses in order to acquire a blood meal. Infestation loads with the cattle tick, Rhipicephalus microplus, are heritable: some breeds carry high loads of reproductively successful ticks, whereas in others, few ticks feed and reproduce efficiently.

Methods

In order to elucidate the mechanisms that result in the different outcomes of infestations with cattle ticks, we examined global gene expression and inflammation induced by tick bites in skins from one resistant and one susceptible breed of cattle that underwent primary infestations with larvae and nymphs of R. microplus. We also examined the expression profiles of genes encoding secreted tick proteins that mediate parasitism in larvae and nymphs feeding on these breeds.

Results

Functional analyses of differentially expressed genes in the skin suggest that allergic contact-like dermatitis develops with ensuing production of IL-6, CXCL-8 and CCL-2 and is sustained by HMGB1, ISG15 and PKR, leading to expression of pro-inflammatory chemokines and cytokines that recruit granulocytes and T lymphocytes. Importantly, this response is delayed in susceptible hosts. Histopathological analyses of infested skins showed inflammatory reactions surrounding tick cement cones that enable attachment in both breeds, but in genetically tick-resistant bovines they destabilized the cone. The transcription data provided insights into tick-mediated activation of basophils, which have previously been shown to be a key to host resistance in model systems. Skin from tick-susceptible bovines expressed more transcripts encoding enzymes that detoxify tissues. Interestingly, these enzymes also produce volatile odoriferous compounds and, accordingly, skin rubbings from tick-susceptible bovines attracted significantly more tick larvae than rubbings from resistant hosts. Moreover, transcripts encoding secreted modulatory molecules by the tick were significantly more abundant in larval and in nymphal salivary glands from ticks feeding on susceptible bovines.

Conclusions

Compared with tick-susceptible hosts, genes encoding enzymes producing volatile compounds exhibit significantly lower expression in resistant hosts, which may render them less attractive to larvae; resistant hosts expose ticks to an earlier inflammatory response, which in ticks is associated with significantly lower expression of genes encoding salivary proteins that suppress host immunity, inflammation and coagulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1945-z) contains supplementary material, which is available to authorized users.

Cell-type deconvolution with immune pathways identifies gene networks of host defense and immunopathology in leprosy

Transcriptome profiles derived from the site of human disease have led to the identification of genes that contribute to pathogenesis, yet the complex mixture of cell types in these lesions has been an obstacle for defining specific mechanisms. Leprosy provides an outstanding model to study host defense and pathogenesis in a human infectious disease, given its clinical spectrum, which interrelates with the host immunologic and pathologic responses. Here, we investigated gene expression profiles derived from skin lesions for each clinical subtype of leprosy, analyzing gene coexpression modules by cell-type deconvolution. In lesions from tuberculoid leprosy patients, those with the self-limited form of the disease, dendritic cells were linked with MMP12 as part of a tissue remodeling network that contributes to granuloma formation. In lesions from lepromatous leprosy patients, those with disseminated disease, macrophages were linked with a gene network that programs phagocytosis. In erythema nodosum leprosum, neutrophil and endothelial cell gene networks were identified as part of the vasculitis that results in tissue injury. The present integrated computational approach provides a systems approach toward identifying cell-defined functional networks that contribute to host defense and immunopathology at the site of human infectious disease.

Epicutaneous immunotherapy for food allergy as a novel pathway for oral tolerance induction

Epicutaneous immunotherapy is a developing technique, aiming at desensitizing patients with food allergy with less risks that oral ingestion or injection could generate. Several clinical trials have been performed and are currently running, in milk and peanut allergy, assessing the safety of the technique and its efficacy. Preclinical models indicate a major role in the mechanisms of desensitization, for example, Tregs and epigenetic modifications.

Identification of skin immune cells in non-human primates

The skin is a valuable target for vaccine delivery because it contains many immune cell populations, notably antigen presenting cells. Skin immune cells have been extensively described in mice and humans but not in non-human primates, which are pertinent models for immunological research in vaccination. The aim of this work was to describe immune cell populations in the epidermis, dermis and skin draining lymph nodes in cynomolgus macaques by a single 12-parameter flow cytometry protocol. Given that skin cells share several markers, we defined a gating strategy to identify accurately immune cells and to limit contamination of one immune cell population by another. The epidermis contained CD1a(+)CD1c(-) Langerhans cells (LCs), CD3(+) T cells and putative NK cells. The dermis contained CD1a(+)CD1c(-) cells, which were similar to LCs, CD1a(+)CD1c(+) dermal dendritic cells (DDCs), CD163(high)CD11b(+) resident macrophages, CD3(+) T cells and putative NK cells. The skin also contained CD66(+) polymorphonuclear cells in some animals. Thus, immune cell populations in the macaque are similar to those in humans despite some differences in phenotype. In skin draining lymph nodes, we identified migratory LCs, CD1a(+)CD1c(+) DDCs and macrophages. The simultaneous identification of these different immune cells with one panel of markers avoids the use of large amounts of precious sample and may improve the understanding of immune mechanisms in the skin after treatment or vaccination.

Human and Mouse Mononuclear Phagocyte Networks: A Tale of Two Species?

Dendritic cells (DCs), monocytes, and macrophages are a heterogeneous population of mononuclear phagocytes that are involved in antigen processing and presentation to initiate and regulate immune responses to pathogens, vaccines, tumor, and tolerance to self. In addition to their afferent sentinel function, DCs and macrophages are also critical as effectors and coordinators of inflammation and homeostasis in peripheral tissues. Harnessing DCs and macrophages for therapeutic purposes has major implications for infectious disease, vaccination, transplantation, tolerance induction, inflammation, and cancer immunotherapy. There has been a paradigm shift in our understanding of the developmental origin and function of the cellular constituents of the mononuclear phagocyte system. Significant progress has been made in tandem in both human and mouse mononuclear phagocyte biology. This progress has been accelerated by comparative biology analysis between mouse and human, which has proved to be an exceptionally fruitful strategy to harmonize findings across species. Such analyses have provided unexpected insights and facilitated productive reciprocal and iterative processes to inform our understanding of human and mouse mononuclear phagocytes. In this review, we discuss the strategies, power, and utility of comparative biology approaches to integrate recent advances in human and mouse mononuclear phagocyte biology and its potential to drive forward clinical translation of this knowledge. We also present a functional framework on the parallel organization of human and mouse mononuclear phagocyte networks.

IL-27 Suppresses Antimicrobial Activity in Human Leprosy

The mechanisms by which intracellular pathogens trigger immunosuppressive pathways are critical for understanding the pathogenesis of microbial infection. One pathway that inhibits host defense responses involves the induction of type I interferons and subsequently IL-10, yet the mechanism by which type I IFN induces IL-10 remains unclear. Our studies of gene expression profiles derived from leprosy skin lesions suggested a link between IL-27 and the IFN-β induced IL-10 pathway. Here, we demonstrate that the IL-27p28 subunit is upregulated following treatment of monocytes with IFN-β and Mycobacterium leprae, the intracellular bacterium that causes leprosy. The ability of IFN-β and M. leprae to induce IL-10 was diminished by IL-27 knockdown. Additionally, treatment of monocytes with recombinant IL-27 was sufficient to induce the production of IL-10. Functionally, IL-27 inhibited the ability of IFN-γ to trigger antimicrobial activity against M. leprae in infected monocytes. At the site of disease, IL-27 was more strongly expressed in skin lesions of patients with progressive lepromatous leprosy, correlating and colocalizing with IFN-β and IL-10 in macrophages. Together, these data provide evidence that in the human cutaneous immune responses to microbial infection, IL-27 contributes to the suppression of host antimicrobial responses.

Recent insights into cutaneous immunization: How to vaccinate via the skin

Technologies and strategies for cutaneous vaccination have been evolving significantly during the past decades. Today, there is evidence for increased efficacy of cutaneously delivered vaccines allowing for dose reduction and providing a minimally invasive alternative to traditional vaccination. Considerable progress has been made within the field of well-established cutaneous vaccination strategies: Jet and powder injection technologies, microneedles, microporation technologies, electroporation, sonoporation, and also transdermal and transfollicular vaccine delivery. Due to recent advances, the use of cutaneous vaccination can be expanded from prophylactic vaccination for infectious diseases into therapeutic vaccination for both infectious and non-infectious chronic conditions. This review will provide an insight into immunological processes occurring in the skin and introduce the key innovations of cutaneous vaccination technologies.

Differential dermal expression of CCL17 and CCL18 in tuberculoid and lepromatous leprosy

BACKGROUND

Leprosy is characterized by polar clinical, histologic and immunological presentations. Previous immunologic studies of leprosy polarity were limited by the repertoire of cytokines known at the time.

METHODOLOGY

We used a candidate gene approach to measure mRNA levels in skin biopsies from leprosy lesions. mRNA from 24 chemokines and cytokines, and 6 immune cell type markers were measured from 85 Nepalese leprosy subjects. Selected findings were confirmed with immunohistochemistry.

PRINCIPAL RESULTS

Expression of three soluble mediators (CCL18, CCL17 and IL-10) and one macrophage cell type marker (CD14) was significantly elevated in lepromatous (CCL18, IL-10 and CD14) or tuberculoid (CCL17) lesions. Higher CCL18 protein expression by immunohistochemistry and a trend in increased serum CCL18 in lepromatous lesions was observed. No cytokines were associated with erythema nodosum leprosum or Type I reversal reaction following multiple comparison correction. Hierarchical clustering suggested that CCL18 was correlated with cell markers CD209 and CD14, while neither CCL17 nor CCL18 were highly correlated with classical TH1 and TH2 cytokines.

CONCLUSIONS

Our findings suggest that CCL17 and CCL18 dermal expression is associated with leprosy polarity.

Targeted delivery of mycobacterial antigens to human dendritic cells via Siglec-7 induces robust T cell activation

Lipids from mycobacteria can be presented to human T cells by group 1 CD1 Ag-presenting molecules (CD1a, CD1b, and CD1c). Group 1 CD1-restricted T cells are activated by lipid Ags presented by myeloid dendritic cells (DCs), after which they generate antibacterial effector functions, including IFN-γ secretion and cytolysis. Thus, mycobacterial lipids are being investigated as components of novel vaccines for mycobacterial infections. In this study we show that the mycobacterial lipid Ag C80 glucose-6-monomycolate can be delivered to human CD1b(+) DCs via targeted liposomal nanoparticles, leading to robust group 1 CD1-restricted activation of T cells. Targeting was achieved by decorating the liposomes with a high-affinity glycan ligand of sialic acid-binding Ig-like lectin (Siglec)-7, a siglec receptor expressed on DCs that mediates rapid endocytosis and transport of its cargo to lysosomes. An Ab to Siglec-7 completely blocked the binding of targeted liposomes to human monocyte-derived DCs (Mo-DCs), demonstrating their targeting specificity. Mo-DCs pulsed with targeted liposomes containing C80 glucose-6-monomycolate more potently activated a CD1b-restricted T cell line relative to Mo-DCs pulsed with free lipid Ag or antigenic liposomes without Siglec-7 ligand. These data suggest that the endocytic function of Siglec-7 can be exploited to deliver glycolipid Ags to their target cell and increase the efficiency of display to T cells.

Antigen-presenting cell candidates for HIV-1 transmission in human distal colonic mucosa defined by CD207 dendritic cells and CD209 macrophages

A common route for HIV-1 infection is sexual transmission across colorectal mucosa, which is thought to be 10-2,000 times more vulnerable to infection than that of the female genital tract. Mucosal surfaces are the first line of defense against many pathogens but the antigen-presenting cells (APCs), key regulators of innate immunity and determinants of adaptive immunity, are not well defined in these target tissues. Using immunohistochemistry, dendritic cells expressing Langerin (CD207(+)), a lectin known to bind and internalize HIV-1, were detected in the periphery of colonic glands and sparsely scattered in the submucosa similarly in colorectal mucosa. This cell type, well known in skin, has generally not been reported in colonic/rectal mucosa. Unexpectedly, the largest APC population observed was a macrophage-like population expressing the well-characterized tissue macrophage markers CD68 and CD163. Confocal microscopy of these cells revealed colocalization of CD209 (DC-SIGN), a presumed dendritic cell marker believed to facilitate HIV-1 transmission, but not other dendritic cell markers. These results show evidence of the unconfirmed presence of Langerhans cells in colorectal mucosa and a predominance of macrophage-like APCs that express CD209 (DC-SIGN). These findings define potential target cells in the pathogenesis of HIV-1 transmission, which may have key implications for the study of early transmission events in normal colorectal mucosa, as well as other infectious diseases and primary immune diseases involving the gut.

Detection of factor XIII-A is a valuable tool for distinguishing dendritic cells and tissue macrophages in granuloma annulare and necrobiosis lipoidica

BACKGROUND

Factor XIII subunit A (FXIII-A) is used as a diagnostic marker in a wide range of dermatological diseases ranging from inflammatory lesions to malignancies, although neither the cell types responsible for its expression nor the mechanism(s) resulting in its local accumulation in pathological conditions have been characterized.

OBJECTIVE

In this study, we aimed to gain information on the cells showing an immunohistochemical reaction for FXIII-A and answer the question whether macrophages and/or dendritic cells are labelled for FXIII-A.

METHODS

We carried out our studies on samples of granuloma annulare (GA) and necrobiosis lipoidica (NL), the prime examples for granulomatous skin lesions with a non-infectious background in which extracellular matrix remodelling is a key feature without any sign of malignant transformation. We used markers for macrophages and dendritic cells in combination with the detection of FXIII-A in double labelling immunohistochemical reactions.

RESULTS

We demonstrated that FXIII-A positivity clearly distinguishes macrophages (CD163+/FXIII-A+) from dendritic cells (CD11c+/FXIII-A-) not only in the normal dermis as previously described by Zaba et al. (J Clin Invest 2007; 117: 2517-2525) but also in the pathological conditions of GA and NL. Detecting the expression of DC-SIGN/CD209 and mannose receptor molecules on FXIII-A+ macrophages we confirmed that FXIII-A is expressed in the alternatively activated macrophages. However, while DC-SIGN/CD209 was invariably expressed on FXIII-A+ cells both in normal and pathological conditions of GA/NL (98.7% vs. 93.5/96%), mannose receptor was only partially coexpressed with FXIII-A (94.8% vs. 74.7/52.2%), suggesting that FXIII-A+ macrophages do not represent a homogenous population.

CONCLUSIONS

FXIII-A selectively marks macrophages and distinguishes them from dendritic cells. The presence of FXIII-A is not a disease-specific marker but indicates a possible common mechanism of macrophage activation in various dermatological diseases.

Human dendritic cell subsets

Dendritic cells are highly adapted to their role of presenting antigen and directing immune responses. Developmental studies indicate that DCs originate independently from monocytes and tissue macrophages. Emerging evidence also suggests that distinct subsets of DCs have intrinsic differences that lead to functional specialisation in the generation of immunity. Comparative studies are now allowing many of these properties to be more fully understood in the context of human immunology.

A three-dimensional atlas of human dermal leukocytes, lymphatics, and blood vessels

Dendritic cells (DCs), macrophages (Mφ), and T cells are major components of the skin immune system, but their interstitial spatial organization is poorly characterized. Using four-channel whole-mount immunofluorescence staining of the human dermis, we demonstrated the three-dimensional distribution of CD31⁺ blood capillaries, LYVE-1⁺ lymphatics, discrete populations of CD11c⁺ myeloid DCs, FXIIIa⁺ Mφ, and lymphocytes. We showed phenotypic and morphological differences in situ between DCs and Mφ. DCs formed the first dermal cellular layer (0–20 μm beneath the dermoepidermal junction), Mφ were located deeper (40–60 μm), and CD3⁺ lymphocytes were observed throughout (0–60 μm). Below this level, DCs, T cells, and the majority of Mφ formed stable perivascular sheaths. Whole-mount imaging revealed the true extent of dermal leukocytes previously underestimated from cross-section views. The total area of apical dermis (0–30 μm) contained approximately 10-fold more myeloid DCs than the entire blood volume of an average individual. Surprisingly, <1% of dermal DCs occupied lymphatics in freshly isolated skin. Dermal DCs rapidly accumulated within lymphatics, but Mφ remained fixed in skin explants cultured ex vivo. The leukocyte architecture observed in normal skin was distorted in inflammation and disease. These studies illustrate the micro-anatomy of dermal leukocytes and provide further insights into their functional organization.

Understanding engineered nanomaterial skin interactions and the modulatory effects of ultraviolet radiation skin exposure

The study of engineered nanomaterials for the development of technological applications, nanomedicine, and nano-enabled consumer products is an ever-expanding discipline as is the concern over the impact of nanotechnology on human environmental health and safety. In this review, we discuss the current state of understanding of nanomaterial skin interactions with a specific emphasis on the effects of ultraviolet radiation (UVR) skin exposure. Skin is the largest organ of the body and is typically exposed to UVR on a daily basis. This necessitates the need to understand how UVR skin exposure can influence nanomaterial skin penetration, alter nanomaterial systemic trafficking, toxicity, and skin immune function. We explore the unique dichotomy that UVR has on inducing both deleterious and therapeutic effects in skin. The subject matter covered in this review is broadly informative and will raise awareness of potential increased risks from nanomaterial skin exposure associated with specific occupational and life style choices. The UVR-induced immunosuppressive response in skin raises intriguing questions that motivate future research directions in the nanotoxicology and nanomedicine fields.

Congenital cutaneous histiocytosis in a piglet

A 2-week-old crossbred male piglet with numerous congenital, variably sized macules, plaques, and papules distributed all over the body was submitted for necropsy. Significant gross and histological lesions were restricted to the skin. On light microscopic examination, these cutaneous lesions corresponded to dermal and/or subcutaneous masses composed of spindle-shaped to round cells that multifocally contained hemosiderin; epidermotropism was not observed. Immunohistochemically, the neoplastic cells were strongly positive for CD204; moderately positive for CD163, lysozyme, and vimentin; and negative for Mac 387, α-1-antitrypsin, S-100 protein and E-cadherin; frozen tissues were not available for CD1a and CD11c. Transmission electron microscopic examination of sections from formalin-fixed tissues did not reveal Birbeck's granules. The clinical, morphological, and immunohistochemical results were consistent with a congenital cutaneous histiocytosis of non-Langerhans cell origin. The condition most resembled juvenile xanthogranuloma in humans, a generally skin-limited non-Langerhans histiocytic disorder that can be congenital. Cutaneous and/or systemic histiocytic disorders are well characterized in dogs and have been described in cats, and a case with some similarities to ours has been reported in a neonatal piglet, but this is to our knowledge the first immunohistochemically supported report of histiocytosis in the pig and congenital histiocytosis in animals.

Transcutaneous antigen delivery system

Transcutaneous immunization refers to the topical application of antigens onto the epidermis. Transcutaneous immunization targeting the Langerhans cells of the skin has received much attention due to its safe, needle-free, and noninvasive antigen delivery. The skin has important immunological functions with unique roles for antigen-presenting cells such as epidermal Langerhans cells and dermal dendritic cells. In recent years, novel vaccine delivery strategies have continually been developed; however, transcutaneous immunization has not yet been fully exploited due to the penetration barrier represented by the stratum corneum, which inhibits the transport of antigens and adjuvants. Herein we review recent achievements in transcutaneous immunization, focusing on the various strategies for the enhancement of antigen delivery and vaccination efficacy. [BMB Reports 2013; 46(1): 17-24]

The physiological role of DC-SIGN: a tale of mice and men

The innate immune receptor DC-SIGN (dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin) was discovered over a decade ago and was initially identified as a pattern recognition receptor. In addition to its ability to recognize a broad range of pathogen-derived ligands and self-glycoproteins, DC-SIGN also mediates intercellular adhesion, as well as antigen uptake and signaling, which is a functional hallmark of dendritic cells (DCs). Most research on DC-SIGN has relied on in vitro studies. The in vivo function of DC-SIGN is difficult to address, in part because there are eight genetic homologs in mice with no clear DC-SIGN ortholog. Here, we summarize the functions attributed to DC-SIGN based on in vitro data and discuss the limitations of available mouse models to uncover the physiological role of this receptor in vivo.

Type I interferon suppresses type II interferon-triggered human anti-mycobacterial responses

Type I interferons (IFN-α and IFN-β) are important for protection against many viral infections, whereas type II interferon (IFN-γ) is essential for host defense against some bacterial and parasitic pathogens. Study of IFN responses in human leprosy revealed an inverse correlation between IFN-β and IFN-γ gene expression programs. IFN-γ and its downstream vitamin D-dependent antimicrobial genes were preferentially expressed in self-healing tuberculoid lesions and mediated antimicrobial activity against the pathogen Mycobacterium leprae in vitro. In contrast, IFN-β and its downstream genes, including interleukin-10 (IL-10), were induced in monocytes by M. leprae in vitro and preferentially expressed in disseminated and progressive lepromatous lesions. The IFN-γ-induced macrophage vitamin D-dependent antimicrobial peptide response was inhibited by IFN-β and by IL-10, suggesting that the differential production of IFNs contributes to protection versus pathogenesis in some human bacterial infections.

Immunology of the maternal-fetal interface

The immune cells that reside at the interface between the placenta and uterus are thought to play many important roles in pregnancy. Recent work has revealed that the composition and function of these cells are locally controlled by the specialized uterine stroma (the decidua) that surrounds the implanted conceptus. Here, I discuss how key immune cell types (natural killer cells, macrophages, dendritic cells, and T cells) are either enriched or excluded from the decidua, how their function is regulated within the decidua, and how they variously contribute to pregnancy success or failure. The discussion emphasizes the relationship between human and mouse studies. Deeper understanding of the immunology of the maternal-fetal interface promises to yield significant insight into the pathogenesis of many human pregnancy complications, including preeclampsia, intrauterine growth restriction, spontaneous abortion, preterm birth, and congenital infection.