CC chemokine receptor (CCR)4 and the CCR10 ligand cutaneous T cell-attracting chemokine (CTACK) in lymphocyte trafficking to inflamed skin

Topical application of a CCL22-binding aptamer suppresses contact allergy

Allergic contact dermatitis is a prevalent occupational disease with limited therapeutic options. The chemokine CCL22, a ligand of the chemokine receptor CCR4, directs the migration of immune cells. Here, it is shown that genetic deficiency of CCL22 effectively ameliorated allergic reactions in contact hypersensitivity (CHS), a commonly used mouse model of allergic contact dermatitis. For the pharmacological inhibition of CCL22, DNA aptamers specific for murine CCL22 were generated by the systematic evolution of ligands by exponential enrichment (SELEX). Nine CCL22-binding aptamers were initially selected and functionally tested in vitro. The 29-nt DNA aptamer AJ102.29m profoundly inhibited CCL22-dependent T cell migration and did not elicit undesired Toll-like receptor-dependent immune activation. AJ102.29m efficiently ameliorated CHS in vivo after systemic application. Moreover, CHS-associated allergic symptoms were also reduced following topical application of the aptamer on the skin. Microscopic analysis of skin treated with AJ102.29m ex vivo demonstrated that the aptamer could penetrate into the epidermis and dermis. The finding that epicutaneous application of the aptamer AJ102.29m in a cream was as effective in suppressing the allergic reaction as intraperitoneal injection paves the way for therapeutic use of aptamers beyond the current routes of systemic administration.

Immune cell trafficking: a novel perspective on the gut-skin axis

Immune cell trafficking, an essential mechanism for maintaining immunological homeostasis and mounting effective responses to infections, operates under a stringent regulatory framework. Recent advances have shed light on the perturbation of cell migration patterns, highlighting how such disturbances can propagate inflammatory diseases from their origin to distal organs. This review collates and discusses current evidence that demonstrates atypical communication between the gut and skin, which are conventionally viewed as distinct immunological spheres, in the milieu of inflammation. We focus on the aberrant, reciprocal translocation of immune cells along the gut-skin axis as a pivotal factor linking intestinal and dermatological inflammatory conditions. Recognizing that the translation of these findings into clinical practices is nascent, we suggest that therapeutic strategies aimed at modulating the axis may offer substantial benefits in mitigating the widespread impact of inflammatory diseases.

Tissue-resident memory T cells: decoding intra-organ diversity with a gut perspective

Tissue-resident memory T cells (TRM) serve as the frontline of host defense, playing a critical role in protection against invading pathogens. This emphasizes their role in providing rapid on-site immune responses across various organs. The physiological significance of TRM is not just confined to infection control; accumulating evidence has revealed that TRM also determine the pathology of diseases such as autoimmune disorders, inflammatory bowel disease, and cancer. Intensive studies on the origin, mechanisms of formation and maintenance, and physiological significance of TRM have elucidated the transcriptional and functional diversity of these cells, which are often affected by local cues associated with their presence. These were further confirmed by the recent remarkable advancements of next-generation sequencing and single-cell technologies, which allow the transcriptional and phenotypic characterization of each TRM subset induced in different microenvironments. This review first overviews the current knowledge of the cell fate, molecular features, transcriptional and metabolic regulation, and biological importance of TRM in health and disease. Finally, this article presents a variety of recent studies on disease-associated TRM, particularly focusing and elaborating on the TRM in the gut, which constitute the largest and most intricate immune network in the body, and their pathological relevance to gut inflammation in humans.

Resident memory T cells in nonlesional skin and healed lesions of patients with chronic inflammatory diseases: Appearances can be deceptive

Tissue-resident memory T (TRM) cells serve as a first line of defense in peripheral tissues to protect the organism against foreign pathogens. However, autoreactive TRM cells are increasingly implicated in autoimmunity, as evidenced in chronic autoimmune and inflammatory skin conditions. This highlights the need to characterize their phenotype and understand their role for the purpose of targeting them specifically without affecting local immunity. To date, the investigation of TRM cells in human skin diseases has focused mainly on lesional tissues of patients. Accumulating evidence suggests that self-reactive TRM cells are still present in clinically healed lesions of patients and play a role in disease flares, but TRM cells also populate skin that is apparently normal. This review discusses the ontogeny of TRM cells in the skin as well as recent insights regarding the presence of self-reactive TRM cells in both clinically healed skin and nonlesional skin of patients with autoimmune and inflammatory skin conditions, with a particular focus on psoriasis, atopic dermatitis, and vitiligo.

IFNγ induces epithelial reprogramming driving CXCL11-mediated T cell migration

The cytokine interferon-gamma (IFNγ) plays a multifaceted role in intestinal immune responses ranging from anti-to pro-inflammatory depending on the setting. Here, using a 3D co-culture system based on human intestinal epithelial organoids, we explore the capacity of IFNγ-exposure to reprogram intestinal epithelia and thereby directly modulate lymphocyte responses. IFNγ treatment of organoids led to transcriptional reprogramming, marked by a switch to a pro-inflammatory gene expression profile, including transcriptional upregulation of the chemokines CXCL9, CXCL10, and CXCL11. Proteomic analysis of organoid-conditioned medium post-treatment confirmed chemokine secretion. Furthermore, IFNγ-treatment of organoids led to enhanced T cell migration in a CXCL11-dependent manner without affecting T cell activation status. Taken together, our results suggest a specific role for CXCL11 in T cell recruitment that can be targeted to prevent T cell trafficking to the inflamed intestine.

Localization, tissue biology and T cell state - implications for cancer immunotherapy

Tissue localization is a critical determinant of T cell immunity. CD8+ T cells are contact-dependent killers, which requires them to physically be within the tissue of interest to kill peptide-MHC class I-bearing target cells. Following their migration and extravasation into tissues, T cells receive many extrinsic cues from the local microenvironment, and these signals shape T cell differentiation, fate and function. Because major organ systems are variable in their functions and compositions, they apply disparate pressures on T cells to adapt to the local microenvironment. Additional complexity arises in the context of malignant lesions (either primary or metastatic), and this has made understanding the factors that dictate T cell function and longevity in tumours challenging. Moreover, T cell differentiation state influences how cues from the microenvironment are interpreted by tissue-infiltrating T cells, highlighting the importance of T cell state in the context of tissue biology. Here, we review the intertwined nature of T cell differentiation state, location, survival and function, and explain how dysfunctional T cell populations can adopt features of tissue-resident memory T cells to persist in tumours. Finally, we discuss how these factors have shaped responses to cancer immunotherapy.

From the Skin to Distant Sites: T Cells in Psoriatic Disease

Human skin has long been known as a protective organ, acting as a mechanical barrier towards the external environment. More recent is the acquisition that in addition to this fundamental role, the complex architecture of the skin hosts a variety of immune and non-immune cells playing preeminent roles in immunological processes aimed at blocking infections, tumor progression and migration, and elimination of xenobiotics. On the other hand, dysregulated or excessive immunological response into the skin leads to autoimmune reactions culminating in a variety of skin pathological manifestations. Among them is psoriasis, a multifactorial, immune-mediated disease with a strong genetic basis. Psoriasis affects 2-3% of the population; it is associated with cardiovascular comorbidities, and in up to 30% of the cases, with psoriatic arthritis. The pathogenesis of psoriasis is due to the complex interplay between the genetic background of the patient, environmental factors, and both innate and adaptive responses. Moreover, an autoimmune component and the comprehension of the mechanisms linking chronic skin inflammation with systemic and joint manifestations in psoriatic patients is still a major challenge. The understanding of these mechanisms may offer a valuable chance to find targetable molecules to treat the disease and prevent its progression to severe systemic conditions.

Tissue adaptation and clonal segregation of human memory T cells in barrier sites

T lymphocytes migrate to barrier sites after exposure to pathogens, providing localized immunity and long-term protection. Here, we obtained blood and tissues from human organ donors to examine T cells across major barrier sites (skin, lung, jejunum), associated lymph nodes, lymphoid organs (spleen, bone marrow), and in circulation. By integrating single-cell protein and transcriptome profiling, we demonstrate that human barrier sites contain tissue-resident memory T (T_RM) cells that exhibit site-adapted profiles for residency, homing and function distinct from circulating memory T cells. Incorporating T cell receptor and transcriptome analysis, we show that circulating memory T cells are highly expanded, display extensive overlap between sites and exhibit effector and cytolytic functional profiles, while T_RM clones exhibit site-specific expansions and distinct functional capacities. Together, our findings indicate that circulating T cells are more disseminated and differentiated, while T_RM cells exhibit tissue-specific adaptation and clonal segregation, suggesting that strategies to promote barrier immunity require tissue targeting.

Molecular pathogenesis of Cutaneous T cell Lymphoma: Role of chemokines, cytokines, and dysregulated signaling pathways

Cutaneous T cell lymphomas (CTCLs) are a heterogeneous group of lymphoproliferative neoplasms that exhibit a wide spectrum of immune-phenotypical, clinical, and histopathological features. The biology of CTCL is complex and remains elusive. In recent years, the application of next-generation sequencing (NGS) has evolved our understanding of the pathogenetic mechanisms, including genetic aberrations and epigenetic abnormalities that shape the mutational landscape of CTCL and represent one of the important pro-tumorigenic principles in CTCL initiation and progression. Still, identification of the major pathophysiological pathways including genetic and epigenetic components that mediate malignant clonal T cell expansion has not been achieved. This is of prime importance given the role of malignant T cell clones in fostering T helper 2 (Th2)-bias tumor microenvironment and fueling progressive immune dysregulation and tumor cell growth in CTCL patients, manifested by the secretion of Th2-associated cytokines and chemokines. Alterations in malignant cytokine and chemokine expression patterns orchestrate the inflammatory milieu and influence the migration dynamics of malignant clonal T cells. Here, we highlight recent insights about the molecular mechanisms of CTCL pathogenesis, emphasizing the role of cytokines, chemokines, and associated downstream signaling networks in driving immune defects, malignant transformation, and disease progression. In-depth characterization of the CTCL immunophenotype and tumoral microenvironment offers a facile opportunity to expand the therapeutic armamentarium of CTCL, an intractable malignant skin disease with poor prognosis and in dire need of curative treatment approaches.

Bitter taste receptor T2R38 is expressed on skin-infiltrating lymphocytes and regulates lymphocyte migration

Bitter taste receptors (T2Rs) are G protein-coupled receptors involved in the perception of bitter taste on the tongue. In humans, T2Rs have been found in several sites outside the oral cavity. Although T2R38 has been reported to be expressed on peripheral lymphocytes, it is poorly understood whether T2R38 plays immunological roles in inflammatory skin diseases such as atopic dermatitis (AD). Then, we first confirmed that T2R38 gene expression was higher in lesional skin of AD subjects than healthy controls. Furthermore, skin T2R38 expression levels were correlated with serum thymus and activation-regulated chemokine and IgE levels in AD patients. In lesional skin of AD, section staining revealed that CD3⁺ T cells in the dermis were T2R38 positive. In addition, flow cytometry analysis showed T2R38 expression in skin T cells. Migration assays using T2R38-transduced Jurkat T cell leukemia cells revealed that T2R38 agonists exerted a dose-dependent migration inhibitory effect. Moreover, skin tissue extracts, as well as supernatants of cultured HaCaT keratinocytes, caused T2R38-dependent migration inhibition, indicating that there should be an endogenous ligand for T2R38 in the skin epidermis. These findings implicate T2R38 as a migratory inhibitory receptor on the skin-infiltrating lymphocytes and as a therapeutic target for allergic/inflammatory skin diseases.

Emerging Anti-Inflammatory Pharmacotherapy and Cell-Based Therapy for Lymphedema

Secondary lymphedema is a common complication of lymph node dissection or radiation therapy for cancer treatment. Conventional therapies such as compression sleeve therapy, complete decongestive physiotherapy, and surgical therapies decrease edema; however, they are not curative because they cannot modulate the pathophysiology of lymphedema. Recent advances reveal that the activation and accumulation of CD4+ T cells are key in the development of lymphedema. Based on this pathophysiology, the efficacy of pharmacotherapy (tacrolimus, anti-IL-4/IL-13 antibody, or fingolimod) and cell-based therapy for lymphedema has been demonstrated in animal models and pilot studies. In addition, mesenchymal stem/stromal cells (MSCs) have attracted attention as candidates for cell-based lymphedema therapy because they improve symptoms and decrease edema volume in the long term with no serious adverse effects in pilot studies. Furthermore, MSC transplantation promotes functional lymphatic regeneration and improves the microenvironment in animal models. In this review, we focus on inflammatory cells involved in the pathogenesis of lymphedema and discuss the efficacy and challenges of pharmacotherapy and cell-based therapies for lymphedema.

CCL27 is a crucial regulator of immune homeostasis of the skin and mucosal tissues

Abundant immune cells reside in barrier tissues. Understanding the regulation of these cells can yield insights on their roles in tissue homeostasis and inflammation. Here, we report that the chemokine CCL27 is critical for establishment of resident lymphocytes and immune homeostasis in barrier tissues. CCL27 expression is associated with normal skin and hair follicle development independent of commensal bacterial stimulation, indicative of a homeostatic role for the chemokine. Accordingly, in the skin of CCL27-knockout mice, there is a reduced presence and dysregulated localization of T cells that express CCR10, the cognate receptor to CCL27. Besides, CCL27-knockout mice have overreactive skin inflammatory responses in an imiquimod-induced model of psoriasis. Beyond the skin, CCL27-knockout mice have increased infiltration of CCR10⁺ T cells into lungs and reproductive tracts, the latter of which also exhibit spontaneous inflammation. Our findings demonstrate that CCL27 is critical for immune homeostasis across barrier tissues.

Retention of Donor T Cells in Lymphohematopoietic Tissue and Augmentation of Tissue PD-L1 Protection for Prevention of GVHD While Preserving GVL Activity

Allogeneic hematopoietic cell transplantation (Allo-HCT) is a curative therapy for hematological malignancies (i.e., leukemia and lymphoma) due to the graft-versus-leukemia (GVL) activity mediated by alloreactive T cells that can eliminate residual malignant cells and prevent relapse. However, the same alloreactive T cells can cause a serious side effect, known as graft-versus-host disease (GVHD). GVHD and GVL occur in distinct organ and tissues, with GVHD occurring in target organs (e.g., the gut, liver, lung, skin, etc.) and GVL in lympho-hematopoietic tissues where hematological cancer cells primarily reside. Currently used immunosuppressive drugs for the treatment of GVHD inhibit donor T cell activation and expansion, resulting in a decrease in both GVHD and GVL activity that is associated with cancer relapse. To prevent GVHD, it is important to allow full activation and expansion of alloreactive T cells in the lympho-hematopoietic tissues, as well as prevent donor T cells from migrating into the GVHD target tissues, and tolerize infiltrating T cells via protective mechanisms, such as PD-L1 interacting with PD-1, in the target tissues. In this review, we will summarize major approaches that prevent donor T cell migration into GVHD target tissues and approaches that augment tolerization of the infiltrating T cells in the GVHD target tissues while preserving strong GVL activity in the lympho-hematopoietic tissues.

T-cell subsets in the skin and their role in inflammatory skin disorders

T lymphocytes (T cells) are major players of the adaptive immune response. Naive T cells are primed in the presence of cytokines, leading to polarization into distinct T-cell subsets with specific functions. These subsets are classified based on their T-cell receptor profile, expression of transcription factors, surface cytokine and chemokine receptors, and their cytokine production, which together determine their specific function. This review provides an overview of the various T-cell subsets and their function in several inflammatory skin disorders ranging from allergic inflammation to skin tumors. Moreover, we highlight similarities of T-cell responses across different skin disorders, demonstrating the presence of similar and opposing functions for the different T-cell subsets. Finally, we discuss the effects of currently available and promising therapeutic approaches to harness T cells in inflammatory skin diseases for which efficacy next to unwanted side effects provide new insights into the pathophysiology of skin disorders.

Motility Matters: How CD8+ T-Cell Trafficking Influences Effector and Memory Cell Differentiation

Immunological memory is a hallmark of adaptive immunity that confers long-lasting protection from reinfections. Memory CD8⁺ T cells provide protection by actively scanning for their cognate antigen and migrating into inflamed tissues. Trafficking patterns of CD8⁺ T cells are also a major determinant of cell fate outcomes during differentiation into effector and memory cell states. CD8⁺ T-cell trafficking must therefore be dynamically and tightly regulated to ensure that CD8⁺ T cells arrive at the correct locations and differentiate to acquire appropriate effector functions. This review aims to discuss the importance of CD8⁺ T-cell trafficking patterns in regulating effector and memory differentiation, maintenance, and reactivation.

Identification of Genes Encoding Antimicrobial Proteins in Langerhans Cells

Langerhans cells (LCs) reside in the epidermis where they are poised to mount an antimicrobial response against microbial pathogens invading from the outside environment. To elucidate potential pathways by which LCs contribute to host defense, we mined published LC transcriptomes deposited in GEO and the scientific literature for genes that participate in antimicrobial responses. Overall, we identified 31 genes in LCs that encode proteins that contribute to antimicrobial activity, ten of which were cross-validated in at least two separate experiments. Seven of these ten antimicrobial genes encode chemokines, CCL1, CCL17, CCL19, CCL2, CCL22, CXCL14 and CXCL2, which mediate both antimicrobial and inflammatory responses. Of these, CCL22 was detected in seven of nine transcriptomes and by PCR in cultured LCs. Overall, the antimicrobial genes identified in LCs encode proteins with broad antibacterial activity, including against Staphylococcus aureus, which is the leading cause of skin infections. Thus, this study illustrates that LCs, consistent with their anatomical location, are programmed to mount an antimicrobial response against invading pathogens in skin.

The complexity of T cell-mediated penicillin hypersensitivity reactions

Penicillin refers to a group of beta-lactam antibiotics that are the first-line treatment for a range of infections. However, they also possess the ability to form novel antigens, or neoantigens, through haptenation of proteins and can stimulate a range of immune-mediated adverse reactions-collectively known as drug hypersensitivity reactions (DHRs). IgE-mediated reactions towards these neoantigens are well studied; however, IgE-independent reactions are less well understood. These reactions usually manifest in a delayed manner as different forms of cutaneous eruptions or liver injury consistent with priming of an immune response. Ex vivo studies have confirmed the infiltration of T cells into the site of inflammation, and the subsets of T cells involved appear dependent on the nature of the reaction. Here, we review the evidence that has led to our current understanding of these immune-mediated reactions, discussing the nature of the lesional T cells, the characterization of drug-responsive T cells isolated from patient blood, and the potential mechanisms by which penicillins enter the antigen processing and presentation pathway to stimulate these deleterious responses. Thus, we highlight the need for a more comprehensive understanding of the underlying genetic and molecular basis of penicillin-induced DHRs.

CCL27 Signaling in the Tumor Microenvironment

Chemokines are a group of small proteins which play an important role in leukocyte migration and invasion. They are also involved in the cellular proliferation and migration of tumor cells.Chemokine CCL27 (cutaneous T cell-attracting chemokine, CTACK) is mainly expressed by keratinocytes of the normal epidermis. It is well known that this chemokine plays an important role in several inflammatory diseases of the skin, such as atopic dermatitis, contact dermatitis, and psoriasis. Moreover, several studies have shown an association between CCL27 expression and a variety of neoplasms including skin cancer.In this chapter, we address the role of chemokine CCL27 in the tumor microenvironment in the most relevant cancers of the skin and other anatomical locations. We also make a brief comment on future perspectives and the potential relation of CCL27 with different immunotherapeutic modalities.

Silk fibroin hydrogel as mucosal vaccine carrier: induction of gastric CD4+TRM cells mediated by inflammatory response induces optimal immune protection against Helicobacter felis

Tissue-resident memory T (T_RM) cells, located in the epithelium of most peripheral tissues, constitute the first-line defense against pathogen infections. Our previous study reported that gastric subserous layer (GSL) vaccination induced a “pool” of protective tissue-resident memory CD4+T (CD4+T_RM) cells in the gastric epithelium. However, the mechanistic details how CD4+T_RM cells form in the gastric epithelium are unknown. Here, our results suggested that the vaccine containing CCF in combination with Silk fibroin hydrogel (SF) broadened the distribution of gastric intraepithelial CD4+T_RM cells. It was revealed that the gastric intraepithelial T_RM cells were even more important than circulating memory T cells against infection by Helicobacter felis. It was also shown that gastric-infiltrating neutrophils were involved as indispensable mediators which secreted CXCL10 to chemoattract CXCR3+CD4+T cells into the gastric epithelium. Blocking of CXCR3 or neutrophils significantly decreased the number of gastric intraepithelial CD4+T_RM cells due to reduced recruitment of CD4+T cells. This study demonstrated the protective efficacy of gastric CD4+T_RM cells against H. felis infection, and highlighted the influence of neutrophils on gastric intraepithelial CD4+T_RM cells formation.

Activated melanoma vessels: A sticky point for successful immunotherapy

Metastatic melanoma is a devastating disease with a marginal-albeit increasing-hope for cure. Melanoma has a high mutation rate which correlates to the expression of numerous neo-antigens and thus is associated with the potential to induce and strengthen effective antitumoral immunity. However, the incomplete and potentially insufficient response to established immunotherapies (response rates usually do not markedly exceed 60%) already points to the need of further studies to improve treatment strategies. Multiple tumor escape mechanisms that allow melanoma to evade from antitumoral immune responses have been characterized and must be overcome to achieve a better clinical efficacy of immunotherapies. Recently, promising progress has been made in targeting tumor vasculature to control and increase the infiltration of tumors with effector lymphocytes. It has been hypothesized that amplified lymphocytic infiltrates in melanoma metastases result in a switch of the tumor microenvironment from a non-inflammatory to an inflammatory state. In this view point essay, we discuss the requirements for successful homing of lymphocytes to melanoma tissue and we present a mouse melanoma xenograft model that allows the investigation of human tumor vessels in vivo. Furthermore, current clinical studies dealing with the activation of melanoma vasculature for enhanced effectiveness of immunotherapy protocols are presented and open questions for routine clinical application are addressed.

Memory CD8+ T Cells Balance Pro- and Anti-inflammatory Activity by Reprogramming Cellular Acetate Handling at Sites of Infection

Serum acetate increases upon systemic infection. Acutely, assimilation of acetate expands the capacity of memory CD8⁺ T cells to produce IFN-γ. Whether acetate modulates memory CD8⁺ T cell metabolism and function during pathogen re-encounter remains unexplored. Here we show that at sites of infection, high acetate concentrations are being reached, yet memory CD8⁺ T cells shut down the acetate assimilating enzymes ACSS1 and ACSS2. Acetate, being thus largely excluded from incorporation into cellular metabolic pathways, now had different effects, namely (1) directly activating glutaminase, thereby augmenting glutaminolysis, cellular respiration, and survival, and (2) suppressing TCR-triggered calcium flux, and consequently cell activation and effector cell function. In vivo, high acetate abundance at sites of infection improved pathogen clearance while reducing immunopathology. This indicates that, during different stages of the immune response, the same metabolite-acetate-induces distinct immunometabolic programs within the same cell type.

Circulating inflammatory mediators as biomarkers of ocular toxoplasmosis in acute and in chronic infection

Toxoplasmosis is highly endemic worldwide. In Brazil, depending on the geographical region and socioeconomic status, 40-70% of individuals become seropositive at some point in their lives. A significant proportion of Toxoplasma gondii-chronically infected individuals who are otherwise immunocompetent develop recurrent ocular lesions. The inflammatory/immune mechanisms involved in development of ocular lesion are still unknown and, despite previous investigation, there are no reliable immune biomarkers to predict/follow disease outcome. To better understand the impact of the immune response on parasite control and immunopathology of ocular toxoplasmosis, and to provide insights on putative biomarkers for disease monitoring, we assessed the production of a large panel of circulating immune mediators in a longitudinal study of patients with postnatally acquired toxoplasmosis stratified by the presence of ocular involvement, both at the early acute stage and 6 months later during chronic infection, correlating them with presence of ocular involvement. We found that T. gondii-infected patients, especially during the acute stage of the disease, display high levels of chemokines, cytokines, and growth factors involved in the activation, proliferation, and migration of inflammatory cells to injured tissues. In particular, major increases were found in the IFN-induced chemokines CXCL9 and CXCL10 in T. gondii-infected patients regardless of disease stage or clinical manifestations. Moreover, a specific subgroup of circulating cytokines and chemokines including GM-CSF, CCL25, CCL11, CXCL12, CXCL13, and CCL2 was identified as potential biomarkers that accurately distinguish different stages of infection and predict the occurrence of ocular toxoplasmosis. In addition to serving as predictors of disease development, these host inflammatory molecules may offer promise as candidate targets for therapeutic intervention.

Cutaneous barrier leakage and gut inflammation drive skin disease in Omenn syndrome

Background

Severe early-onset erythroderma and gut inflammation, with massive tissue infiltration of oligoclonal activated T cells are the hallmark of Omenn syndrome (OS).

Objective

The impact of altered gut homeostasis in the cutaneous manifestations of OS remains to be clarified.

Methods

We analyzed a cohort of 15 patients with OS and the 129Sv/C57BL/6 knock-in Rag2^R229Q/R229Q (Rag2^R229Q) mouse model. Homing phenotypes of circulating lymphocytes were analyzed by flow cytometry. Inflammatory cytokines and chemokines were examined in the sera by ELISA and in skin biopsies by immunohistochemistry and in situ RNA hybridization. Experimental colitis was induced in mice by dextran sulfate sodium salt.

Results

We show that memory/activated T cells from patients with OS and from the Rag2^R229Q mouse model of OS abundantly express the skin homing receptors cutaneous lymphocyte associated antigen and CCR4 (Ccr4), associated with high levels of chemokine C-C motif ligands 17 and 22. Serum levels of LPS are also elevated. A broad T_h1/T_h2/T_h17 inflammatory signature is detected in the periphery and in the skin. Increased Tlr4 expression in the skin of Rag2^R229Q mice is associated with enhanced cutaneous inflammation on local and systemic administration of LPS. Likewise, boosting colitis in Rag2^R229Q mice results in increased frequency of Ccr4⁺ splenic T cells and worsening of skin inflammation, as indicated by epidermal thickening, enhanced epithelial cell activation, and dermal infiltration by T_h1 effector T cells.

Conclusions

These results support the existence of an interplay between gut and skin that can sustain skin inflammation in OS.

Cytokines/Chemokines: Novel Biomarkers Associated with Severe Cutaneous Adverse Reactions

Although the incidence of severe cutaneous adverse reactions (SCARs) is very low, if it is not diagnosed and treated in time, it can not only cause skin and mucous membrane involvement, but can also cause multiple organ failure and even death. The diagnostic criteria and treatment guidelines for severe drug eruptions have not been unified. Many medical centers have used human leukocyte antigen alleles to diagnose SCARs. Some prospective studies have shown that susceptibility gene testing can prevent SCARs as early as possible, but the widespread implementation of its technology is limited by being ethnically specific. With the unique advantages of cytokine detection technology, cytokines are increasingly important for the diagnosis and treatment of SCARs. Related cytokines/chemokines involved in the pathogenesis, adjuvant diagnosis, and treatment of SCARs are discussed.

Insights Into the Molecular and Cellular Underpinnings of Cutaneous T Cell Lymphoma

Cutaneous T cell lymphoma (CTCL) is a rare malignancy of skin-homing T lymphocytes. Advances in whole exome sequencing have identified a vast number of both single nucleotide variants (SNVs) and genomic copy number alterations (GCNAs) as driver mutations present in CTCL cells. These alterations cluster within several key pathways - T cell/NF-κB/JAK-STAT activation, cell cycle dysregulation/apoptosis, and DNA structural dysregulation affecting gene expression - allowing the maintenance of a population of proliferating, activated malignant T lymphocytes. While much of the clinical spectrum, genetic alterations, and oncogenic behavior of CTCL have been elucidated, little is known about the etiology that underlies CTCL malignant transformation and progression. Herein, we review the epidemiology, clinical presentation, and pathophysiology of CTCL to provide a perspective on CTCL pathogenesis. We outline a series of alterations by which mature, activated T lymphocytes are endowed with apoptosis resistance and cutaneous persistence. Subsequent genomic alterations including the loss of chromosomal structural controls further promote proliferation and constitutive T cell activation. CTCL cells are both malignant cells and highly functional T cells that can have major cutaneous and immunologic effects on the patient, including the suppression of cell-mediated immunity that facilitates malignant cell expansion. A deeper understanding of the molecular and cellular underpinnings of CTCL can help guide clinical management as well as inform prognosis and therapeutic discovery.

Drug-induced gingival hyperplasia: An in vitro study using amlodipine and human gingival fibroblasts

Gingival overgrowth is a serious side effect that accompanies the use of amlodipine. Several conflicting theories have been proposed to explain the fibroblast’s function in gingival overgrowth. To determine whether amlodipine alters the inflammatory responses, we investigated its effects on gingival fibroblast gene expression as compared with untreated cells. Fragments of gingival tissue of healthy volunteers (11 years old boy, 68 years old woman, and 20 years old men) were collected during operation. Gene expression of 29 genes was investigated in gingival fibroblast cell culture treated with amlodipine, compared with untreated cells. Among the studied genes, only 15 (CCL1, CCL2D, CCL5, CCL8, CXCL5, CXCL10, CCR1, CCR10, IL1A, IL1B, IL5, IL7, IL8, SPP1, and TNFSF10) were significantly deregulated. In particular, the most evident overexpressed genes in treated cells were CCR10 and IL1A. These results seem to indicate a possible role of amlodipine in the inflammatory response of treated human gingival fibroblasts.

Targeted therapy guided by single-cell transcriptomic analysis in drug-induced hypersensitivity syndrome: a case report

Drug-induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DiHS/DRESS) is a potentially fatal multiorgan inflammatory disease associated with herpesvirus reactivation and subsequent onset of autoimmune diseases1-4. Pathophysiology remains elusive and therapeutic options are limited. Cases refractory to corticosteroid therapy pose a clinical challenge1,5 and approximately 30% of patients with DiHS/DRESS develop complications, including infections and inflammatory and autoimmune diseases1,2,5. Progress in single-cell RNA sequencing (scRNA-seq) provides an opportunity to dissect human disease pathophysiology at unprecedented resolutions6, particularly in diseases lacking animal models, such as DiHS/DRESS. We performed scRNA-seq on skin and blood from a patient with refractory DiHS/DRESS, identifying the JAK-STAT signaling pathway as a potential target. We further showed that central memory CD4+ T cells were enriched with DNA from human herpesvirus 6b. Intervention via tofacitinib enabled disease control and tapering of other immunosuppressive agents. Tofacitinib, as well as antiviral agents, suppressed culprit-induced T cell proliferation in vitro, further supporting the roles of the JAK-STAT pathway and herpesviruses in mediating the adverse drug reaction. Thus, scRNA-seq analyses guided successful therapeutic intervention in the patient with refractory DiHS/DRESS. scRNA-seq may improve our understanding of complicated human disease pathophysiology and provide an alternative approach in personalized medicine.

Chemokine-Adjuvanted Plasmid DNA Induces Homing of Antigen-Specific and Non-Antigen-Specific B and T Cells to the Intestinal and Genital Mucosae

Plasmid DNA is a promising vaccine platform that together with electroporation can elicit significant systemic Ab responses; however, immunity at mucosal sites remains low. In this study, we sought to program T and B cells to home to the gastrointestinal and vaginal mucosae using genetic chemokine adjuvants and assessed their impact on immune homeostasis in various distinct immune compartments. BALB/c mice were immunized i.m. with plasmid DNA encoding a model Ag HIV-1 Env gp140 and selected chemokines/cytokine and boosted intravaginally with gp140 recombinant protein. Isolated splenocytes, intestinal lymphocytes, and genital lymphocytes as well as serum and intestinal luminal contents were assessed for Ag-specific reactivity. In addition, flow cytometric analysis was performed to determine the impact on immune homeostasis at these sites. Different molecular chemokine/cytokine adjuvants effected significant alterations to the recruitment of B and T cells to the spleen, vaginal and intestinal mucosae, for example CCL25 enhanced splenic and vaginal Ag-specific T cell responses whereas CCL28 increased the levels of specific T cells only in the vaginal mucosa. The levels of Ab could be modulated in the systemic circulation, as well as the vaginal vault and intestinal lumen, with CCL20 playing a central role. Our data demonstrate that the CCL20, CCL25, and CCL28 genetic chemokine adjuvants enhance the vaccine Ag-specific humoral and cellular responses and induce homing to the intestinal and female genital mucosae.

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.

Shifting Paradigms in Allergic Contact Dermatitis: The Role of Innate Immunity

The role of the innate immune system in allergic contact dermatitis (ACD) has traditionally been confined to the initial antigen sensitization phase. However, more recent findings have shown the role of innate immunity in additional aspects of ACD, including the effector phase of the classic type IV hypersensitivity reaction. As a result, the precise immunologic mechanisms mediating ACD are more complex than previously believed. The aim of this review is to provide insight into recent advances in understanding the role of the innate immune system in the pathogenesis of ACD, including novel mechanistic roles for macrophages, innate lymphoid cells, natural killer cells, innate γδ T cells, and other signaling molecules. These insights provide new opportunities for therapeutic intervention in ACD.

A CCL1/CCR8-dependent feed-forward mechanism drives ILC2 functions in type 2-mediated inflammation

Group 2 innate lymphoid cells (ILC2s) possess indispensable roles during type 2-mediated inflammatory diseases. Although their physiological and detrimental immune functions seem to depend on the anatomical compartment they reside, their tissue tropism and the molecular and immunological processes regulating the self-renewal of the local pool of ILC2s in the context of inflammation or infection are incompletely understood. Here, we analyzed the role of the CC-chemokine receptor CCR8 for the biological functions of ILC2s. In vitro and in vivo experiments indicated that CCR8 is in comparison to the related molecule CCR4 less important for migration of these cells. However, we found that activated mouse and human ILC2s produce the CCR8 ligand CCL1 and are a major source of CCL1 in vivo. CCL1 signaling to ILC2s regulates their proliferation and supports their capacity to protect against helminthic infections. In summary, we identify a novel chemokine receptor-dependent mechanism by which ILC2s are regulated during type 2 responses.

Microenvironmental immune cell signatures dictate clinical outcomes for PTCL-NOS

Peripheral T-cell lymphoma (PTCL), not otherwise specified (PTCL-NOS) is among the most common disease subtypes of PTCL, one that exhibits heterogeneous clinicopathological features. Although multiple disease-stratification models, including the cell-of-origin or gene-expression profiling methods, have been proposed for this condition, their clinical significance remains unclear. To establish a clinically meaningful stratification model, we analyzed gene-expression signatures of tumors and tumor-infiltrating immune cells using the nCounter system, which enables accurate quantification of low abundance and/or highly fragmented transcripts. To do so, we assessed transcripts of 120 genes related to cancer or immune cells using tumor samples from 68 newly diagnosed PTCL-NOS patients and validated findings by immunofluorescence in tumor sections. We show that gene-expression signatures representing tumor-infiltrating immune cells, but not those of cancerous T cells, dictate patient clinical outcomes. Cases exhibiting both B-cell and dendritic cell (DC) signatures (BD subgroup) showed favorable clinical outcomes, whereas those exhibiting neither B-cell nor DC signatures (non-BD subgroup) showed extremely poor prognosis. Notably, half of the non-BD cases exhibited a macrophage signature, and macrophage infiltration was evident in those cases, as revealed by immunofluorescence. Importantly, tumor-infiltrating macrophages expressed the immune-checkpoint molecules programmed death ligand 1/2 and indoleamine 2, 3-dioxygenase 1 at high levels, suggesting that checkpoint inhibitors could serve as therapeutic options for patients in this subgroup. Our study identifies clinically distinct subgroups of PTCL-NOS and suggests a novel therapeutic strategy for 1 subgroup associated with a poor prognosis. Our data also suggest functional interactions between cancerous T cells and tumor-infiltrating immune cells potentially relevant to PTCL-NOS pathogenesis.

A Comprehensive Profile of Chemokine Gene Expression in the Tissues of the Female Reproductive Tract in Mice

Homeostatic leukocyte trafficking into and within the female reproductive tract (FRT) contributes to fertility and reproductive health. It is unclear how this process is regulated in the anatomically distinct reproductive tissues, or whether the genes involved are affected by cyclical changes in reproductive hormones. In tissues such as skin and intestine, mouse studies have defined evolutionarily conserved molecular mechanisms for tissue-specific homing, interstitial positioning, and leukocyte egress. Chemokine family members are invariably involved, with the chemokine expression profile of a tissue regulating leukocyte content. Reproductive tissues (ovary, vagina, cervix, uterine horn) of 8 week old virgin female C57BL/6 mice (n = 20) were collected, and expression of mRNA for leukocyte markers and chemokines conducted by qPCR. Lymphocytic and myeloid cell populations within the uterus, cervix, bone marrow and PALN from virgin C57BL/6 mice were determined by flow cytometric analysis. Variation in leukocyte content between reproductive tissues is evident, with the uterus and cervix containing complex mixtures of lymphocytes and myeloid cells. Twenty-six chemokine genes are expressed in the FRT, many by several component tissues, some preferentially by one. Most striking are Xcl1 and Ccl28, which are restricted to the uterus. Ccl20 and genes encoding CXCR2 ligands are primarily transcribed in cervix and vagina. Ovary shows the lowest expression of most chemokine genes, with the notable exception of Ccl21 and Ccl27. We also identify eight chemokines in the vagina whose expression fluctuates substantially across the oestrous cycle. These data reveal complex chemokine networks within the FRT, and provide a framework for future studies of homeostatic leukocyte trafficking into and within these tissues.Abbreviations: BM: bone marrow; DC: dendritic cell; DN: double negative; FRT: female reproductive tract; FSC: forward scatter; NK: natural killer; PALN: para-aortic lymph node; SSC: side scatter; Tregs: regulatory T cells.

The Roles of Liver-Resident Lymphocytes in Liver Diseases

Tissue-resident lymphocytes usually reside in barrier sites and are involved in innate and adaptive immunity. In recent years, many studies have shown that multiple types of lymphocytes are resident in the liver, including memory CD8⁺ T (T_RM) cells; "unconventional" T cells, such as invariant natural killer T (iNKT) cells, mucosal associated invariant T (MAIT) cells, and γδT cells; innate lymphoid cells (ILCs) such as natural killer (NK) cells and other ILCs. Although diverse types of tissue-resident lymphocytes share similar phenotypes, functional properties, and transcriptional regulation, the unique microenvironment of the liver can reshape their phenotypic and functional characteristics. Liver-resident lymphocytes serve as sentinels and perform immunosurveillance in response to infection and non-infectious insults, and are involved in the maintenance of liver homeostasis. Under the pathological conditions, distinct liver-resident lymphocytes exert protective or pathological effects in the process of various liver diseases. In this review, we highlight the unique properties of liver-resident lymphocytes, and discuss their functional characteristics in different liver diseases.

T-cell positioning by chemokines in autoimmune skin diseases

Autoimmune skin diseases are complex processes in which autoreactive cells must navigate through the skin tissue to find their targets. Regulatory T cells in the skin help to mitigate autoimmune inflammation and may in fact be responsible for the patchy nature of these conditions. In this review, we will discuss chemokines that are important for global recruitment of T cell populations to the skin during disease, as well as signals that fine-tune their localization and function. We will describe prototypical disease responses and chemokine families that mediate these responses. Lastly, we will include an overview of chemokine-targeting drugs that have been tested as new treatment strategies for autoimmune skin diseases.

The Interplay Between Lymphatic Vessels and Chemokines

Chemokines are a family of small protein cytokines that act as chemoattractants to migrating cells, in particular those of the immune system. They are categorized functionally as either homeostatic, constitutively produced by tissues for basal levels of cell migration, or inflammatory, where they are generated in association with a pathological inflammatory response. While the extravasation of leukocytes via blood vessels is a key step in cells entering the tissues, the lymphatic vessels also serve as a conduit for cells that are recruited and localized through chemoattractant gradients. Furthermore, the growth and remodeling of lymphatic vessels in pathologies is influenced by chemokines and their receptors expressed by lymphatic endothelial cells (LECs) in and around the pathological tissue. In this review we summarize the diverse role played by specific chemokines and their receptors in shaping the interaction of lymphatic vessels, immune cells, and other pathological cell types in physiology and disease.

Regulation of Immune Function by the Lymphatic System in Lymphedema

The lymphatic vasculature has traditionally been thought to play a passive role in the regulation of immune responses by transporting antigen presenting cells and soluble antigens to regional lymph nodes. However, more recent studies have shown that lymphatic endothelial cells regulate immune responses more directly by modulating entry of immune cells into lymphatic capillaries, presenting antigens on major histocompatibility complex proteins, and modulating antigen presenting cells. Secondary lymphedema is a disease that develops when the lymphatic system is injured during surgical treatment of cancers or is damaged by infections. We have used mouse models of lymphedema in order to understand the effects of chronic lymphatic injury on immune responses and have shown that lymphedema results in a mixed T helper cell and T regulatory cell (Treg) inflammatory response. Prolonged T helper 2 biased immune responses in lymphedema regulate the pathology of this disease by promoting tissue fibrosis, inhibiting formation of collateral lymphatics, decreasing lymphatic vessel pumping capacity, and increasing lymphatic leakiness. Treg infiltration following lymphatic injury results from proliferation of natural Tregs and suppresses innate and adaptive immune responses. These studies have broad clinical relevance since understanding how lymphatic injury in lymphedema can modulate immune responses may provide a template with which we can study more subtle forms of lymphatic injury that may occur in physiologic conditions such as aging, obesity, metabolic tumors, and in the tumor microenvironment.

Cytokine, Chemokine, and Cytokine Receptor Changes Are Associated With Metabolic Improvements After Bariatric Surgery

Context

Altered cytokine levels and chronic low-grade inflammation contribute to metabolic dysfunction in obesity. The extent of cytokine changes and their impact on metabolic improvements after bariatric surgery have not been fully explored.

Objective

To compare 76 circulating cytokines, chemokines, and secreted cytokine receptors in subjects with obesity and lean subjects and determine how these cytokines are altered by bariatric surgery.

Design, Setting, and Participants

A total of 37 patients with obesity and 37 lean patients in a cross-sectional study at an academic medical center. We also investigated cytokine changes in 25 patients with obesity after bariatric surgery.

Intervention

Bariatric surgery (Roux-en-Y gastric bypass and vertical sleeve gastrectomy).

Main Outcome Measures

Quantification of 76 circulating cytokines, chemokines, and secreted cytokine receptors.

Results

A total of 13 cytokines were significantly higher, and 4 lower, in patients with obesity relative to lean controls. Soluble vascular endothelial growth factor receptor 2 (sVEGFR2), soluble TNF receptor (sTNFR) 1, and sTNFR2 were positively correlated, and soluble receptor for advanced glycation end-products was inversely correlated, with weight and body mass index. sTNFR2 was positively correlated with fasting glucose, homeostatic model assessment of insulin resistance, and hemoglobin A1c. After bariatric surgery, adiponectin increased, and leptin decreased. Elevated sVEGFR2 levels in patients with obesity were decreased (P = 0.01), whereas reduced chemokine (C-X-C motif) ligand (CXCL) 12 levels in patients with obesity increased (P = 0.03) after surgery. Patients with higher soluble interleukin receptor (sIL) 1R2 and sIL-6R levels before surgery had greater weight loss after surgery (P < 0.05).

Conclusions

We demonstrate that chemokine (C-C motif) ligand (CCL) 14, sVEGFR2, and platelet-derived growth factor BB are elevated in obesity, and CXCL12, CCL11, and CCL27 are lower in obesity. We found clinically concordant directionality between lean and patients with obesity and before vs after surgery for six cytokines, suggesting that bariatric surgery shifted the cytokine profiles of patients with obesity toward that of lean controls.

Aspects of intradermal immunization with different adjuvants: The role of dendritic cells and Th1/Th2 response

Intradermal (i.d.) application of vaccine is promising way how to induce specific immune response against particular pathogens. Adjuvants, substances added into vaccination dose with the aim to increase immunogenicity, play important role in activation of dendritic cells with subsequent activation of lymphocytes. They can, however, induce unwanted local reactions. The aim of the study was to determine the effect of i.d. administration of model antigen keyhole limped hemocyanine alone or with different adjuvants-aluminium hydroxide and oil-based adjuvants-on local histopathological reaction as well as dendritic cell activation at the site of administration and local cytokine and chemokine response. This was assessed at 4 and 24 hours after application. Selection of the adjuvants was based on the fact, that they differently enhance antibody or cell-mediated immunity. The results showed activation of dendritic cells and both Th1 and Th2 response stimulated by oil-based adjuvants. It was associated with higher expression of set of genes, incl. chemokine receptor CCR7 or Th1-associated chemokine CXCL10 and cytokine IFNγ. Application of the antigen with aluminium hydroxide induced higher expression of Th2-associated IL4 or IL13. On the other hand, both complete and incomplete Freund´s adjuvants provoked strong local reaction associated with influx of neutrophils. This was accompanied with high expression of proinflammatory IL1 or neutrophil chemoattractant CXCL8. Surprisingly, similarly strong local reaction was detected also after application of aluminium hydroxide-based adjuvant. The best balanced local reaction with sufficient activation of immune cells was detected after application of oil-based adjuvants Montanide and Emulsigen.

Evaluation of Lymphocyte Migration to Induced Paederus Dermatitis: An Experimental Study in Rats

Background:

Paederus dermatitis (PD) is a blistering disorder that is caused by a small insect of the genus Paederus, especially Paederus fuscipes. This study aimed to investigate the reaction of the adaptive immune system regarding the recruitment of CD3, CCR4, and CCR10 markers, which are specifically expressed on the surface of T lymphocytes.

Materials and Methods:

In this experimental study, 24 female rats were divided into two groups: the test and the negative control. In the test group, PD was induced by making insects in contact with shaved rat skin. Biopsies were obtained 24, 72, and 120 h after induction. In the negative control group, physiological saline was applied. Specimens were evaluated by immunohistochemical staining method. Antibodies against CD3, CCR4, and CCR10 were used. Distribution and staining intensities of CD3, CCR4, and CCR10 markers were estimated by the H-score index and findings were analyzed using the Kruskal–Wallis and Wilcoxon statistical tests.

Results:

Based on the results of immunohistochemistry, the expression of CD3, CCR4, and CCR10 in the test group at 24, 72, and 120 h compared to the control group showed significant increase (P = 0.0006, P = 0.001, and P < 0.0001), respectively. The peak of expression of all markers was at 72 h after exposure. Hematoxylin and eosin staining also confirmed the fact that the majority of the lymphocyte infiltration occurred at 72 h postexposure.

Conclusion:

The expression of CD3, CCR4, and CCR10 on cells present in PD lesions could indicate that T-lymphocytes are recruited to the site of inflammation by chemokine–chemokine receptor interactions and hence provide evidence for the response by the adaptive immune system following a PD.

Primary Cutaneous T-Cell Lymphomas: Mycosis Fungoides and Sezary Syndrome

Mycosis fungoides and Sézary syndrome are the most common subtypes of all primary cutaneous lymphomas and represent complex diseases that require a multidisciplinary assessment by dermatologists, oncologists, and pathologists. Staging and work-up are critical to guarantee an optimal treatment plan that includes skin-directed and/or systemic regimens depending on the clinical stage, tumor burden, drug-related side effect profile, and patient comorbidities. However, there is no cure and patients frequently relapse, requiring repeated treatment courses for disease control. The study of the tumor microenvironment and molecular mechanisms of these rare neoplasms may assist in the development of new immune therapies providing promising treatment approaches tailored for patients with relapse/refractory disease.

Targeting Chemokines and Chemokine Receptors in Melanoma and Other Cancers

The tumor microenvironment is highly heterogeneous. It is composed of a diverse array of immune cells that are recruited continuously into lesions. They are guided into the tumor through interactions between chemokines and their receptors. A variety of chemokine receptors are expressed on the surface of both tumor and immune cells rendering them sensitive to multiple stimuli that can subsequently influence their migration and function. These features significantly impact tumor fate and are critical in melanoma control and progression. Indeed, particular chemokine receptors expressed on tumor and immune cells are strongly associated with patient prognosis. Thus, potential targeting of chemokine receptors is highly attractive as a means to quench or eliminate unconstrained tumor cell growth.

A Task Force Against Local Inflammation and Cancer: Lymphocyte Trafficking to and Within the Skin

The skin represents a specialized site for immune surveillance consisting of resident, inflammatory and memory populations of lymphocytes. The entry and retention of T cells, B cells, and ILCs is tightly regulated to facilitate detection of pathogens, inflammation and tumors cells. Loss of individual or multiple populations in the skin may break tolerance or increase susceptibility to tumor growth and spread. Studies have significantly advanced our understanding of the role of skin T cells and ILCs at steady state and in inflammatory settings such as viral challenge, atopy, and autoimmune inflammation. The knowledge raised by these studies can benefit to our understanding of immune cell trafficking in primary melanoma, shedding light on the mechanisms of tumor immune surveillance and to improve immunotherapy. This review will focus on the T cells, B cells, and ILCs of the skin at steady state, in inflammatory context and in melanoma. In particular, we will detail the core chemokine and adhesion molecules that regulate cell trafficking to and within the skin, which may provide therapeutic avenues to promote tumor homing for a team of lymphocytes.

CCL17/TARC and CCR4 expression in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, highly aggressive neuroendocrine skin cancer. In more than 80% of the cases, Merkel cell polyomavirus (MCPyV) is a causal factor. The oncogenic potential of MCPyV is mediated through its viral oncoproteins, large T antigen (LT) and small t antigen (sT). To investigate the role of cytokines in MCC, a PCR array analysis for genes encoding inflammatory cytokines and receptors was performed on MCPyV-negative and MCPyV-positive MCC cell lines, respectively. We detected an increased expression of CCL17/TARC in the MCPyV-positive MKL2 cell line compared to the MCPyV-negative MCC13 cell line. Transfection studies in MCC13 cells with LT expression plasmid, and a luciferase reporter plasmid containing the CCL17/TARC promoter, exhibited stimulated promoter activity. Interestingly, the ectopic expression of CCL17/TARC upregulated MCPyV early and late promoter activities in MCC13 cells. Furthermore, recombinant CCL17/TARC activated both the mitogen-activated protein kinase and the NF-κB pathways. Finally, immunohistochemical staining on human MCC tissues showed a strong staining of CCL17/TARC and its receptor CCR4 in both LT-positive and -negative MCC. Taken together, CCL17/TARC and CCR4 may be a potential target in MCC therapy providing MCC patients with a better overall survival outcome.

Peripheral Tissue Chemokines: Homeostatic Control of Immune Surveillance T Cells

Cellular immunity is governed by a complex network of migratory cues that enable appropriate immune cell responses in a timely and spatially controlled fashion. This review focuses on the chemokines and their receptors regulating the steady-state localisation of immune cells within healthy peripheral tissues. Steady-state immune cell traffic is not well understood but is thought to involve constitutive (homeostatic) chemokines. The recent discovery of tissue-resident memory T cells (T_RM cells) illustrates our need for understanding how chemokines control immune cell mobilisation and/or retention. These studies will be critical to unravel novel pathways for preserving tissue function (aging) and preventing tissue disease (vaccination).

Effect of Lactobacillus strains on thymus and chemokine expression in keratinocytes and development of atopic dermatitis-like symptoms

Lactobacillus strains, a major group of lactic acid bacteria, are representative food microorganisms that have many potential beneficial effects via their interactions with immune and intestinal epithelial cells. However, little is known about the effect of Lactobacillus strains on atopic dermatitis via keratinocytes, which comprise the physical barrier of the skin. In this study, we report that Lactobacillus strains have a significant suppressive effect on tumour necrosis factor (TNF)-α-induced expression and production of thymus and activation-regulated chemokine (TARC), a T helper 2 cell chemokine responsible for atopic dermatitis, in human keratinocytes. An RNA interference study showed that the effect of Lactobacillus reuteri strain Japan Collection of Microorganisms (JCM) 1112, the most suppressive strain, depended on the presence of Toll-like receptor 2 and the induction of A20 (also known as TNF-α-induced protein 3) and cylindromatosis in HaCaT cells. Topical application of a water-soluble extract of homogenised JCM 1112 cells significantly suppressed the development of house dust mite-induced atopic skin lesions and TARC expression at the lesion sites in NC/Nga mice. Our study provides new insights into the use of Lactobacillus strains as suppressive agents against keratinocyte-involved atopic inflammation of the skin.