Skin-associated Lymphoid Tissue Research Articles

Innate Immune Responses of Skin Mucosa in Common Carp (Cyprinus Carpio) Fed a Diet Supplemented with Galactooligosaccharides.

Simple SummaryThe skin mucosa in fish is equipped with innate immune mechanisms, which constitute the first line of defense against potentially harmful factors in the aquatic environment. Prebiotics, such as galactooligosaccharides (GOS), mediate modulation of the immune responses. Dietary prebiotics promote the development of intestinal microbiota, which interacts with the immune system. In this study, we analyzed the effects of the GOS prebiotic applied as a feed additive on molecular responses in the skin mucosa of the common carp. The genes analyzed encode various proteins associated with the innate immune response in skin mucosa in fish, such as mucin secretion, antimicrobial peptides, and enzymes. Modulated expression of those genes at the mRNA level regulates the defense mechanisms in the skin mucosa. In this study, supplementation with GOS increased the mRNA level of interferon and lysozyme, which are involved in fighting infection. At the same time, GOS decreased the mRNA level of CRP, which is a marker of inflammation. We conclude that supplementation with GOS modulates innate immune processes in the skin mucosa of common carp. Further studies could be focused on analyzing the effects of GOS on the microbiota composition of the skin mucosa and the mitigating effects against environmental stress.Galactooligosaccharides (GOS) are well-known immunomodulatory prebiotics. We hypothesize that GOS supplemented in feed modulates innate immune responses in the skin-associated lymphoid tissue (SALT) of common carp. The aim of this study was to determine the impact of GOS on mRNA expression of the immune-related genes in skin mucosa. During the feeding trial, the juvenile fish (bodyweight 180 ± 5 g) were fed two types of diet for 50 days: control and supplemented with 2% GOS. At the end of the trial, a subset of fish was euthanized (n = 8). Skin mucosa was collected, and RNA was extracted. Gene expression analysis was performed with RT-qPCR to determine the mRNA abundance of the genes associated with innate immune responses in SALT, i.e., acute-phase protein (CRP), antimicrobial proteins (His2Av and GGGT5L), cytokines (IL1β, IL4, IL8, IL10, and IFNγ), lectin (CLEC4M), lyzosymes (LyzC and LyzG), mucin (M5ACL), peroxidase (MPO), proteases (CTSB and CTSD), and oxidoreductase (TXNL). The geometric mean of 40s s11 and ACTB was used to normalize the data. Relative quantification of the gene expression was calculated with ∆∆Ct. GOS upregulated INFγ (p ≤ 0.05) and LyzG (p ≤ 0.05), and downregulated CRP (p ≤ 0.01). We conclude that GOS modulates innate immune responses in the skin mucosa of common carp.

Role of Lymphoid Structure in Skin Immunity.

The skin is the outermost organ of the body and is exposed to many kinds of external pathogens. To manage this, the skin contains multiple types of immune cells. To achieve sufficient induction of cutaneous adaptive immune responses, the antigen presentation/recognition in the skin is an essential process. Recent studies have expanded our knowledge of how T cells survey their cognate antigens in the skin. In addition, the formation of a lymphoid cluster, named inducible skin-associated lymphoid tissue (iSALT), has been reported during skin inflammation. Although iSALT may not be classified as a typical tertiary lymphoid organ, it provides specific antigen presentation sites in the skin. In this article, we provide an overview of the antigen presentation mechanism in the skin, with a focus on the development of iSALT and its function.

Organization of the Skin Immune System and Compartmentalized Immune Responses in Infectious Diseases.

The skin is an organ harboring several types of immune cells that participate in innate and adaptive immune responses. The immune system of the skin comprises both skin cells and professional immune cells that together constitute what is designated skin-associated lymphoid tissue (SALT). In this review, I extensively discuss the organization of SALT and the mechanisms involved in its responses to infectious diseases of the skin and mucosa. The nature of these SALT responses, and the cellular mediators involved, often determines the clinical course of such infections. I list and describe the components of innate immunity, such as the roles of the keratinocyte barrier and of inflammatory and natural killer cells. I also examine the mechanisms involved in adaptive immune responses, with emphasis on new cytokine profiles, and the role of cell death phenomena in host-pathogen interactions and control of the immune responses to infectious agents. Finally, I highlight the importance of studying SALT in order to better understand host-pathogen relationships involving the skin and detail future directions in the immunological investigation of this organ, especially in light of recent findings regarding the skin immune system.

Antigen presentation and adaptive immune responses in skin.

For the induction of adequate cutaneous immune responses, the antigen presentation and recognition that occur in both the skin and skin-draining lymph nodes are essential. In each process of cutaneous immune responses, several distinct subsets of immune cells, including dendritic cells and T cells, are involved, and they elicit their respective functions in a harmonious manner. For example, in the elicitation phase of cutaneous acquired immunity, immune cells form a specific lymphoid structure named inducible skin-associated lymphoid tissue (iSALT) to facilitate efficient antigen presentation in situ. In this short review, we will overview the mechanisms of how antigens are presented and how cutaneous adaptive immune responses are conducted in the skin, especially focusing on contact hypersensitivity, a prototypic adaptive immune response in the skin.

The Change of Teleost Skin Commensal Microbiota Is Associated With Skin Mucosal Transcriptomic Responses During Parasitic Infection by Ichthyophthirius multifillis.

Teleost skin serves as the first line of defense against invading pathogens, and contain a skin-associated lymphoid tissue (SALT) that elicit gut-like immune responses against antigen stimulation. Moreover, exposed to the water environment and the pathogens therein, teleost skin is also known to be colonized by diverse microbial communities. However, little is known about the interactions between microbiota and the teleost skin mucosal immune system, especially dynamic changes about the interactions under pathogen infection. We hypothesized that dramatic changes of microbial communities and strong mucosal immune response would be present in the skin of aquatic vertebrate under parasite infection. To confirm this hypothesis, we construct an infected model with rainbow trout (Oncorhynchus mykiss), which was experimentally challenged by Ichthyophthirius multifiliis (Ich). H & E staining of trout skin indicates the successful invasion of Ich and shows the morphological changes caused by Ich infection. Critically, increased mRNA expression levels of immune-related genes were detected in trout skin from experimental groups using qRT-PCR, which were further studied by RNA-Seq analysis. Here, through transcriptomics, we detected that complement factors, pro-inflammatory cytokines, and antimicrobial genes were strikingly induced in the skin of infected fish. Moreover, high alpha diversity values of microbiota in trout skin from the experimental groups were discovered. Interestingly, we found that Ich infection led to a decreased abundance of skin commensals and increased colonization of opportunistic bacteria through 16S rRNA pyrosequencing, which were mainly characterized by lose of Proteobacteria and increased intensity of Flavobacteriaceae. To our knowledge, our results suggest for the first time that parasitic infection could inhibit symbionts and offer opportunities for other pathogens' secondary infection in teleost skin.

Understanding the Basis of Transcutaneous Vaccine Delivery

Under many circumstances, prophylactic immunizations are considered as the only possible strategy to control infectious diseases. Considerable efforts are typically invested in immunogen selection but, erroneously, the route of administration is not usually a major concern despite the fact that it can strongly influence efficacy. The skin is now considered a key component of the lymphatic system with tremendous potential as a target for vaccination. The purpose of this review is to present the immunological basis of the skin-associated lymphoid tissue, so as to provide understanding of the skin vaccination strategies. Several strategies are currently being developed for the transcutaneous delivery of antigens. The classical, mechanical or chemical disruptions versus the newest approaches based on microneedles for antigen delivery through the skin are discussed herein.

The immunological anatomy of the skin.

The skin is the outermost organ of the body and is continuously exposed to external pathogens. Upon inflammation, various immune cells pass through, reside in or are recruited to the skin to orchestrate diverse cutaneous immune responses. To achieve this, immune cells interact with each other and even communicate with non-immune cells, including peripheral nerves and the microbiota. Immunologically important anatomical sites, such as skin appendages (for example, hair follicles and sweat glands) or postcapillary venules, act as special portal sites for immune cells and for establishing tertiary lymphoid structures, including inducible skin-associated lymphoid tissue. Here, we provide an overview of the key findings and concepts of cutaneous immunity in association with skin anatomy and discuss how cutaneous immune cells fine-tune physiological responses in the skin.

IL-21 Attenuates FITC-Induced Contact Hypersensitivity Response via Regulation of Dendritic Cell Function.

IL-21 is mainly produced by activated CD4+ T cells and is involved in the activation of immune cells such as Tcells and macrophages. In contrast, IL-21 suppresses dendritic cell maturation. We studied the effect of IL-21 in a mouse model of FITC-induced contact hypersensitivity using IL-21 isoform transgenic (IL-21iso-Tg) mice. Tissue inflammation at 24 hours after elicitation in IL-21iso-Tg mice was significantly weaker than that in wild-type mice. In agreement with tissue inflammation, recruitment of CD4+ and CD8+ T cells, neutrophils, and macrophages into the inflamed tissue was decreased in IL-21iso-Tg mice. In addition, both mRNA expression and protein production of inflammatory cytokines were lower in IL-21iso-Tg mice. In the skin, T cells were activated at inducible skin-associated lymphoid tissue, which is likely a gut-associated lymphoid tissue. The mRNA level of CXCL2, an essential chemokine for inducible skin-associated lymphoid tissue formation, was significantly lower in IL-21iso-Tg mice, and histological analysis showed that dendritic cell clustering, a preliminary step in inducible skin-associated lymphoid tissue formation, was impaired. Our study showed thatIL-21 down-regulated inducible skin-associated lymphoid tissue formation and reduced contact hypersensitivity response.

Possible inducible skin-associated lymphoid tissue (iSALT)-like structures with CXCL13+fibroblast-like cells in secondary syphilis

Possible inducible skin-associated lymphoid tissue (iSALT)-like structures with CXCL13⁺fibroblast-like cells in secondary syphilis

Local immune response of two mucosal surfaces of the European seabass, Dicentrarchus labrax, fed tryptophan- or methionine-supplemented diets

Immune responses relies on an adequate provision of multiple nutrients that sustain the synthesis of key effector molecules. These needs are depicted in the already reported increase of circulating free amino acids in fish under stressful conditions. Since aquaculture and the inherent fish welfare are an emergent call, the immunomodulatory effects of amino acids on gut- and skin-associated lymphoid tissues of the European seabass (Dicentrarchus labrax) were studied under unstressed conditions and after an inflammatory insult. To achieve this goal, fish were distributed in duplicate tanks (fifteen fish per tank) and were fed for 14 days with methionine or tryptophan-supplemented diets at 2× dietary requirement level (MET and TRP, respectively) or a control diet meeting the amino acids requirement levels (CTRL). Afterwards, samples of skin and posterior gut were collected from 6 fish per dietary treatment for the assessment of the immune status while the remaining animals were intraperitoneally-injected with inactivated Photobacterium damselae subsp. piscicida and subsequently sampled either 4 or 24 h post-injection.The immune status of both mucosal surfaces was poorly affected, although a tryptophan effect was denoted after bacterial inoculation, with several immune-related genes up-regulated in the gut at 4 h post-injection, which seems to suggest a neuroendocrine-immune systems interaction. In contrast, skin mucosal immunity was inhibited by tryptophan dietary supplementation. Regarding methionine, results were often statistically non-significant, though increasing trends were denoted in a few parameters.Overall, dietary methionine did not significantly affect neither gut nor skin immunity, whereas tryptophan supplementation seems to induce modulatory mechanisms that might be tissue-specific.

9-Phenanthrol enhances the generation of an CD8+ T cell response following transcutaneous immunization with imiquimod in mice

BackgroundTranscutaneous immunization (TCI) is a non-invasive vaccination strategy targeting the skin-associated lymphoid tissue. Topical application of the TLR7 agonist imiquimod as adjuvant in combination with peptide antigens activates the innate immune system and mounts cytotoxic T lymphocyte (CTL) responses. ObjectiveBased on the commercial 5% imiquimod-containing drug Aldara we aimed to develop an improved formulation with superior vaccination efficiencies. The primary target was the enhancement of mast cell activation as important key for the function of the innate immune system. MethodsWe investigated the effects of 9-phenanthrol (9-phe) on the activation of mast cells in vitro and in vivo. For TCI, we applied 0.2% 9-phe in Aldara or Aldara alone as adjuvants in combination with the MHC class I – restricted peptide SIINFEKL. To monitor vaccination, mast cell degranulation, migration of DC and frequencies of epitope-specific CTL was assessed. In a transgenic tumor model, the efficiencies of prophylactic immunization against a tumor antigen were also monitored. Results9-phe induced degranulation of mast cells in vitro and upon topical application in vivo. A mixture of 0.2% 9-phe in Aldara showed superior results regarding the migration of DC and the expansion of antigen-specific CTL. Consequently, prophylactic immunization with 0.2% 9-phe in Aldara caused enhanced protection against tumor inoculation. ConclusionOur data demonstrate that a simple modification of an adjuvant formulation can yield superior results in experimental vaccination protocols by boosting critical steps leading to the generation of an efficient CTL response.

280 Presence of inducible skin-associated lymphoid tissue (iSALT)-like structures with CXCL13+ fibroblast-like cells in secondary syphilis

280 Presence of inducible skin-associated lymphoid tissue (iSALT)-like structures with CXCL13+ fibroblast-like cells in secondary syphilis

031 Inducible skin-associated lymphoid tissue (iSALT) is detected in the scalp treated with topical immunotherapy for alopecia areata

031 Inducible skin-associated lymphoid tissue (iSALT) is detected in the scalp treated with topical immunotherapy for alopecia areata

Inducible lymphoid clusters, iSALTs, in contact dermatitis: a new concept of acquired cutaneous immune responses.

Antigen presentation to peripheral memory T cells is a key step in the prompt elicitation of acquired immune responses. In the mucosa, specific sentinel lymphoid tissues called mucosa-associated lymphoid tissue serve as antigen presentation sites. Correspondingly, the concept of skin-associated lymphoid tissue (SALT) has been proposed in the 1980s. However, the details of SALT have not been clarified so far. Recently, the live imaging analysis using two photon microscopes are developed. Here, we have identified inducible lymphoid clusters in the skin, we called it inducible SALTs (iSALTs), using a murine contact hypersensitivity model. In the elicitation phase, dendritic cells (DCs) formed clusters and interacted for several hours with effector memory T cells in the dermis. This interaction was essential for proliferation and activation of effector memory T cells in situ in an antigen dependent manner. Interestingly, DC clusters were abrogated by depletion of skin macrophages. Furthermore, IL-1 treatment induced CXCL2 production from macrophages and DC clusters were suppressed with the blockade of IL-1R or CXCR2. Taken together, this sustained conjugation between DCs and memory T cells, iSALTs, is essential for establishment of the effector phase in acquired cutaneous immunity.

Cellular and humoral components of the immune system of the skin

Along with mucous membranes the skin as the main barrier to the outside world creates a system of protection against any influences of the world. It is not only the place of realization of immunological processes, but it also actively participates in them due to the existence of its own elements of the immune system which are able to actively participate in the development of inflammatory reactions and neoplastic processes. Skin cells interact with cells of the immune system by setting a direct contact or by secreting a number of soluble factors, called cytokines, and other protein components such as proteins of the complement system. The general concept of skin-associated lymphoid tissue and skin’s immune system with immunocompetent cells in the epidermis and dermis, for cooperation of which in various stages of the immune response requires identity concerning anti-genes of HLA system, is presented in the review. Thus, specific immunological reaction with antibody formation promote the release of antigen from the body of both exogenous and endogenous origin. However, at violation of any element of immunological protection there is a delay of antigen elimination process, that results in own tissue structural damage. Interaction with foreign antigens (physical, chemical, infectious, etc.), denaturation of its own proteins or disclosure of tissue structures (antigens), that did not contact with immunocompetent cells, promote the formation of autoantigens and the production of autoantibodies against them. Thus, skin is a highly organized structure with a network of immunocompetent cells and soluble mediators. Introduction of molecular and biological methods as a knowledge tool is continually expanding the information about the skin as an organ of the immune system. The gained knowledge will definitely promote the development of new therapeutic approaches to skin diseases.

Distribution of T Cells in Rainbow Trout (Oncorhynchus mykiss) Skin and Responsiveness to Viral Infection.

Although the skin constitutes the first line of defense against waterborne pathogens, there is a great lack of information regarding the skin associated lymphoid tissue (SALT) and whether immune components of the skin are homogeneously distributed through the surface of the fish is still unknown. In the current work, we have analyzed the transcription of several immune genes throughout different rainbow trout (Oncorhynchus mykiss) skin areas. We found that immunoglobulin and chemokine gene transcription levels were higher in a skin area close to the gills. Furthermore, this skin area as well as other anterior sections also transcribed significantly higher levels of many different immune genes related to T cell immunity such as T cell receptor α (TCRα), TCRγ, CD3, CD4, CD8, perforin, GATA3, Tbet, FoxP3, interferon γ (IFNγ), CD40L and Eomes in comparison to posterior skin sections. In agreement with these results, immunohistochemical analysis revealed that anterior skin areas had a higher concentration of CD3+ T cells and flow cytometry analysis confirmed that the percentage of CD8+ T lymphocytes was also higher in anterior skin sections. These results demonstrate for the first time that T cells are not homogeneously distributed throughout the teleost skin. Additionally, we studied the transcriptional regulation of these and additional T cell markers in response to a bath infection with viral hemorrhagic septicemia virus (VHSV). We found that VHSV regulated the transcription of several of these T cell markers in both the skin and the spleen; with some differences between anterior and posterior skin sections. Altogether, our results point to skin T cells as major players of teleost skin immunity in response to waterborne viral infections.

The role of dendritic cells and macrophages in the skin immunity.

The skin is one of the largest organs in the human body, which acts as the primary interface with the external world. In view of its protective role, mammalian skin consists of physical and immunological barriers. The water-impermeable stratum corneum and the tight junctions in the granular layer work at the epidermal level work as the most important first and second "physical" barriers. Upon antigen invasion to the skin, the integrated innate and acquired immune systems in both the epidermis and dermis are activated in a coordinated manner to neutralize the external intruder as the strong third "immunological" barriers. Dendritic cells and macrophages are known to play pivotal roles in such immunological barriers. Intra-vital analysis of the murine skin by two-photon microscopy enabled us to assess the habituate and the direct interactions of various cells in the skin in situ, which reside or infiltrate upon inflammation. We introduce the recent works how dendritic cells and macrophages orchestrate the skin immunity, highlighting the importance of sequential leucocyte cluster formation in the efficient activation of memory T cells in the skin, which can be attributed as 'inducible skin-associated lymphoid tissue (iSALT)'.

Novel concept of iSALT (inducible skin-associated lymphoid tissue) in the elicitation of allergic contact dermatitis.

Allergic contact dermatitis (ACD) is one of the most common inflammatory skin diseases, which is classified as a delayed-type hypersensitivity immune response. The development of ACD is divided into two phases: sensitization and elicitation. In the sensitization phase, antigen-specific effector T cells are induced in the draining lymph nodes by antigen-captured cutaneous dendritic cells (DCs) that migrate from the skin. In the elicitation phase, the effector T cells are activated in the skin by antigen-captured cutaneous DCs and produce various chemical mediators, which create antigen-specific inflammation. In this review, we discuss the recent advancements in the immunological mechanisms of ACD, focusing on the mechanisms in the elicitation phase. The observations of elicitation of CHS lead to the emerging novel concept of iSALT (inducible skin-associated lymphoid tissue).

Immune regulation in pathophysiology and targeted therapy for itch in atopic dermatitis

Abstract Itch is an unpleasant perception that provokes one to desire to scratch. It results from the activation of free nerve endings by noxious stimuli in the skin. Atopic dermatitis (AD) is a prototypic inflammatory skin disease that always occurs with an intense itch. AD involves many components of skin-associated lymphoid tissue (SALT). As a disease with polarized T helper 2 cell activation, AD involves eosinophil infiltration and immunoglobulin E, interleukin (IL)-2, IL-4, IL-13, and IL-31 production. As a disease involving an impaired skin barrier, AD is characterized by the enhanced transepidermal entry of allergens and the production of thymic stromal lymphopoietin (TSLP) from epidermal keratinocytes, which worsen atopic march and disease progression. Both immune and epidermal events interact with cutaneous nerve components, including transient receptor potential (TRP) channels and opioid receptors, causing both the perception and propagation of itch from the skin to the brain. In addition to treating itch through TRP channels and opioid receptors, it might be possible to target the various cellular components of SALT, including keratinocytes, eosinophils, and soluble factors, such as IL-31, IL-4, IL-13, IL-31, and TSLP.

Novel insights into the role of immune cells in skin and inducible skin-associated lymphoid tissue (iSALT)

Novel insights into the role of immune cells in skin and inducible skin-associated lymphoid tissue (iSALT)