CLA+ memory T cells in atopic dermatitis: CLA+ T cells and atopic dermatitis.

Circulating skin-homing cutaneous lymphocyte-associated antigen (CLA)+ T cells constitute a small subset of human memory T cells involved in several aspects of atopic dermatitis: Staphylococcus aureus related mechanisms, the abnormal Th2 immune response, biomarkers, clinical aspects of the patients, pruritus, and the mechanism of action of targeted therapies. Superantigens, IL-13, IL-31, pruritus, CCL17 and early effects on dupilumab-treated patients have in common that they are associated with the CLA+ T cell mechanisms in atopic dermatitis patients. The function of CLA+ T cells corresponds with the role of T cells belonging to the skin-associated lymphoid tissue and could be a reason why they reflect different mechanisms of atopic dermatitis and many other T cell mediated skin diseases. The goal of this review is to gather all this translational information of atopic dermatitis pathology.

Allergen sensitization stratifies IL-31 production by memory T cells in atopic dermatitis patients.

Background: The role of allergen sensitization in IL-31 production by T cells and specifically in the clinical context of atopic dermatitis (AD) has not been characterized. Methods: The response to house dust mite (HDM) in purified memory T cells cocultured with epidermal cells from AD patients (n=58) and control subjects (n=11) was evaluated. AD-associated cytokines from culture supernatants, plasma proteins and mRNA expression from cutaneous lesions were assessed and related with the clinical features of the patients. Results: HDM-induced IL-31 production by memory T cells defined two subsets of AD patients according to the presence or absence of IL-31 response. Patients in the IL-31 producing group showed a more inflammatory profile, and increased HDM-specific (sp) and total IgE levels compared to the IL-31 non-producing group. A correlation between IL-31 production and patient's pruritus intensity, plasma CCL27 and periostin was detected. When the same patients were analyzed based on sp IgE and total IgE levels, an increased IL-31 in vitro response, as well as type 2 markers in plasma and cutaneous lesions, was found in patients with sp IgE levels > 100 kUA/L and total IgE levels > 1000 kU/L. The IL-31 response by memory T cells was restricted to the cutaneous lymphocyte-associated antigen (CLA)+ T-cell subset. Conclusion: IgE sensitization to HDM allows stratifying IL-31 production by memory T cells in AD patients and relating it to particular clinical phenotypes of the disease.

Atopic Dermatitis Pathogenesis: Lessons From Immunology.

Translational research has changed the understanding of atopic dermatitis (AD) pathogenesis beyond the basic mechanisms of immunology. The study in patients of rational therapies based on targeted therapies (biologicals) provides valuable information from the patient and provides lessons of clinical immunology on clinically relevant mechanism of AD pathogenesis. AD features such as skin barrier defect, skin dysbiosis, and pruritus share a common abnormal adaptive immune response process. Skin-homing CLA+CD4+ memory T-cells produce IL-4, IL-13, and IL-31 which are key mediators in AD pathogenesis. Lessons learned from AD show that translational immunology allows generating rational therapies for AD and learning its immunopathogenesis in the patient.

Human CLA+ Memory T Cell and Cytokines in Psoriasis.

Psoriasis is a common inflammatory skin condition resulting from the interplay between epidermal keratinocytes and immunological cellular components. This sustained inflammation is essentially driven by pro-inflammatory cytokines with the IL-23/IL-17 axis playing a critical central role, as proved by the clinical efficacy of their blockade in patients. Among all the CD45R0+ memory T cell subsets, those with special tropism for cutaneous tissues are identified by the expression of the Cutaneous Lymphocyte-associated Antigen (CLA) carbohydrate on their surface, that is induced during T cell maturation particularly in the skin-draining lymph nodes. Because of their ability to recirculate between the skin and blood, circulating CLA+ memory T cells reflect the immune abnormalities found in different human cutaneous conditions, such as psoriasis. Based on this premise, studying the effect of different environmental microbial triggers and psoriatic lesional cytokines on CLA+ memory T cells, in the presence of autologous epidermal cells from patients, revealed important IL-17 cytokines responses that are likely to enhance the pro-inflammatory loop underlying the development of psoriatic lesions. The goal of this mini-review is to present latest data regarding cytokines implicated in plaque and guttate psoriasis immunopathogenesis from the prism of CLA+ memory T cells, that are specifically related to the cutaneous immune system.

The Translational Relevance of Human Circulating Memory Cutaneous Lymphocyte-Associated Antigen Positive T Cells in Inflammatory Skin Disorders.

Circulating memory T cells are heterogeneous in their tissue tropism. The skin-seeking T cell subset expresses the cutaneous lymphocyte-associated antigen (CLA) on their surface. CLA+ memory T cells not only migrate from blood to skin but also recirculate between blood and skin. Studying CLA+ memory T cells in cutaneous diseases has allowed a better understanding of immune-inflammatory mechanisms that take place. The analysis of the phenotypical features of these cells, their antigen specificity, cytokine production profile, and changes in relationship to clinical status and therapies among other characteristics have led to the concept that they constitute peripheral cellular biomarkers in T cell-mediated cutaneous conditions. CLA+ memory T cells are of relevance in the pathogenesis of several cutaneous diseases, such as psoriasis (PSO), atopic dermatitis, vitiligo, and drug-induced allergic reactions, to name a few. The interaction of circulating CLA+ T cells with skin-resident cells has been investigated in different ex vivo coculture models made out of clinical samples. Interestingly, microbes that are present in the skin or related with human skin diseases are preferentially recognized by CLA+ T cells. Thus, the interaction of Streptococcus pyogenes with CLA+ T cells in PSO is providing novel concepts that help to understand disease immunopathogenesis. The goal of this review is to present latest results in the field of CLA+ T cells in T cell-mediated inflammatory skin diseases and their translational relevance for human immunodermatology.

IL-15 and IL-23 synergize to trigger Th17 response by CLA+ T cells in psoriasis.

IL-15 has emerged as a potentially relevant target in the IL-17 response in psoriasis. However, its mechanism is poorly characterized in humans. IL-15 and IL-23 are constitutively expressed in the psoriatic lesion. Also, IL-15 is considered a susceptibility-associated gene in psoriasis, as are IL-23R, and HLACW6. Here, we studied the effect of IL-15 and IL-23 stimulation on the cytokine response of CLA+/CLA- T cells from 9 psoriasis patients and 3 healthy control subjects. To this end, CLA + and CLA- T cells from blood samples were cultured with epidermal cells from skin biopsies and treated with IL-15 and IL-23. After five days of culture, cytokines in supernatant were measured by ELISA or fluorescent bead-based immunoassay. There was a statistically significant increase in IL-17F and IL-17A production (P < .001) in cocultures of psoriasis skin-homing CLA + T cells with epidermal cells when stimulated with IL-15 and IL-23, but this effect was not observed in the cells of healthy controls. Interestingly, this response was reduced by around 50 to 80% by blocking HLA class I and II molecules. Our results point to the synergic action of IL-15 and IL-23 selectively for CLA + cells in psoriasis, leading to the induction of Th17 cell-related cytokines.

Ex vivo culture of lesional psoriasis skin for pharmacological testing.

BACKGROUND: Psoriasis is a chronic, inflammatory skin disorder resulting from a complex interplay between immune and skin cells via release of soluble mediators. While a lot is known about the molecular mechanisms behind psoriasis pathogenesis, there is still a need for preclinical research models that accuratelyreplicate the disease. OBJECTIVE: This study aimed to develop and characterize ex vivo culture of psoriasis skin as a model for pharmacological testing, where the immunological events of psoriasis can be followed. METHODS: Full thickness punch biopsies of lesional psoriasis skin were cultured in submerged conditions up to 144 h followingin situ T cell stimulation with rhIL-23 and anti-CD3 and anti-CD28 antibodies. The T cell mediated skin inflammation was assessed by gene and protein l analysis for a panel of inflammatory mediators. Tissue integrity and morphology were evaluated by histological analysis. RESULTS: T cell stimulation resulted in functional and psoriasis specificin situ activation of T cells. The expression levels of most of the proinflammatory mediators related to both immune and skin cells were comparable to these in freshly isolated tissue at 48 and 96 h of culture. Tissue integrity and morphology were sustained up to 96 h. Treatment with a corticosteroid reduced the expression of several pro-inflammatory cytokines and chemokines, whereas anti-IL-17A antibody treatment reduced the expression of the IL-17A downstream markers IL-8 and DEFB4. CONCLUSION: By preserving keyimmunopathological mechanisms of psoriasis, ex vivo culture of psoriasis skin can be used for the investigation of inflammatory processes of psoriasis and for preclinical drug discovery research.

Specific IgA and CLA+ T-Cell IL-17 Response to Streptococcus pyogenes in Psoriasis.

Streptococcus pyogenes tonsillar infection is well known to trigger and exacerbate psoriasis lesions in both guttate and plaque forms of the disease. Although mucosal and cutaneous tissues are closely involved in psoriasis pathology, the interaction between their specific immune responses has not been deeply explored. This work aims to address and characterize the presence of humoral responses against S. pyogenes in patients with psoriasis and its putative association with cytokine responses detected in vitro in our psoriasis ex vivo model, based on the coculture of cutaneous lymphocyte-associated antigen+/- T cells with autologous epidermal cells. Patients with psoriasis presented increased IgA response to S. pyogenes when compared with control subjects. In patients with plaque psoriasis, despite being negative for anti-streptolysin O antibody titer, IgA plasma levels against S. pyogenes correlated with cutaneous lymphocyte-associated antigen+ T-cell-dependent IL-17F response in vitro. No association is observed for IgG levels in plaque psoriasis. Similar association is observed for IgA anti-S. pyogenes extract and IL-17A in patients with guttate psoriasis. We propose S. pyogenes-specific IgA as a potential new perspective for better understanding the role of S. pyogenes in psoriasis development.

Keratinocyte-specific ablation of Mcpip1 impairs skin integrity and promotes local and systemic inflammation.

MCPIP1 (Regnase-1, encoded by the ZC3H12A gene) regulates the mRNA stability of several inflammatory cytokines. Due to the critical role of this RNA endonuclease in the suppression of inflammation, Mcpip1 deficiency in mice leads to the development of postnatal multiorgan inflammation and premature death. Here, we generated mice with conditional deletion of Mcpip1 in the epidermis (Mcpip1EKO). Mcpip1 loss in keratinocytes resulted in the upregulated expression of transcripts encoding factors related to inflammation and keratinocyte differentiation, such as IL-36α/γ cytokines, S100a8/a9 antibacterial peptides, and Sprr2d/2h proteins. Upon aging, the Mcpip1EKO mice showed impaired skin integrity that led to the progressive development of spontaneous skin pathology and systemic inflammation. Furthermore, we found that the lack of epidermal Mcpip1 expression impaired the balance of keratinocyte proliferation and differentiation. Overall, we provide evidence that keratinocyte-specific Mcpip1 activity is crucial for the maintenance of skin integrity as well as for the prevention of excessive local and systemic inflammation. KEY MESSAGES: Loss of murine epidermal Mcpip1 upregulates transcripts related to inflammation and keratinocyte differentiation. Keratinocyte Mcpip1 function is essential to maintain the integrity of skin in adult mice. Ablation of Mcpip1 in mouse epidermis leads to the development of local and systemic inflammation.

CLA+ T Cell Response to Microbes in Psoriasis.

Streptococcus pyogenes throat infection is a clinically relevant trigger of both guttate and chronic plaque psoriasis, and it provides an ideal context in which to study the pathogenesis of these diseases using an antigen-dependent approach. Circulating cutaneous lymphocyte-associated antigen (CLA) positive (+) memory T cells are a subset of peripheral lymphocytes whose phenotype and function are related to immunological mechanisms in the skin. These cells are considered peripheral biomarkers of T-cell-mediated skin diseases. The coculture of autologous epidermal cells with CLA+ T cells from psoriasis patients activated by S. pyogenes allows the reproduction of the ex vivo initial molecular events that occur during psoriatic lesion formation. With cooperation of autologous epidermal cells, S. pyogenes selectively activates CLA+ T cells both in guttate and plaque psoriasis, inducing key mediators, including an IL-17 response. Here, we explore potential new mechanisms of psoriasis development including the influence of HLA-Cw6 on S. pyogenes CLA+ T cell activation in guttate psoriasis, the relevance of IL-9 on microbe induced IL-17 response in guttate and plaque psoriasis, and novel effector functions of Candida albicans. This review will summarize recent knowledge of psoriatic mechanisms elicited by microbes that have been studied through an innovative translational perspective based on CLA+ T cell-mediated cutaneous immune response.

Microbe-Dependent Induction of IL-9 by CLA+ T Cells in Psoriasis and Relationship with IL-17A.

IL-9 is present in psoriatic lesions and is produced by lymphocytes. However, it is not known whether this cytokine is induced by relevant pathogenic triggers of psoriasis, such as Streptococcus pyogenes. Here we addressed the production of IL-9 in response to various pathogens in a psoriatic ex vivo model. Extracts of S. pyogenes and Candida albicans triggered the production of IL-9 and also IL-17A and IFN-γ. This induction was dependent on the interaction between CLA+ T cells and epidermal cells. Neutralization of IL-9 reduced S. pyogenes-induced IL-17A production by CLA+ T cells but had no effect on IFN-γ production. Also, IL-9 increased the survival of circulating psoriatic CLA+ T cells. Co-cultures from patients with guttate or plaque psoriasis with S. pyogenes produced similar amounts of IL-9. High cytokine responses in streptococcal-driven guttate patients paralleled peaks in Psoriasis Area Severity Index and anti-streptolysin O levels. Our results confirm that IL-9 promotes inflammation in psoriasis by up-regulating IL-17A production and support the clinical association of the immune response by streptococcal-sensitized CLA+ T cells with this cytokine, especially in guttate psoriasis.

MCPIP1 RNase Is Aberrantly Distributed in Psoriatic Epidermis and Rapidly Induced by IL-17A.

ZC3H12A, which encodes the RNase monocyte chemotactic protein-induced protein 1 (MCPIP1), is up-regulated in psoriatic skin and reduced to normal levels after clinical treatments with anti-IL-17A/IL-17R neutralizing antibodies. In IL-17A-stimulated keratinocytes, MCPIP1 is rapidly increased at the transcript and protein levels. Also, IL-17A was found to be the main inducer of ZC3H12A expression in keratinocytes treated with supernatants derived from a Streptococcus pyogenes-activated psoriatic ex vivo model based on the co-culture of psoriatic cutaneous lymphocyte-associated antigen (CLA(+)) T cells and lesional epidermal cells. Moreover, MCPIP1 was aberrantly distributed in the suprabasal layers of psoriatic epidermis. In psoriatic samples, IL-17A-stimulated epidermal cell suspensions showed an increased MCPIP1 expression, especially in the mid-differentiated cellular compartment. The knockdown of ZC3H12A showed that this RNase participates in the regulation of the mRNAs present in suprabasal differentiated keratinocytes. Furthermore, JAK/STAT3 inhibition prevented the IL-17A-dependent induction of MCPIP1. In the mouse model of imiquimod-induced psoriasis, Zc3h12a expression was abrogated in Il17ra(-/-) mice. These results support the notion that IL-17A-mediated induction of MCPIP1 is involved in the regulation of local altered gene expression in suprabasal epidermal layers in psoriasis.

Streptococcus pyogenes-induced cutaneous lymphocyte antigen-positive T cell-dependent epidermal cell activation triggers TH17 responses in patients with guttate psoriasis.

BACKGROUND: Guttate psoriasis (GP) is characterized by acute onset of small, rounded psoriatic lesions. Although this particular phenotype of psoriasis is usually associated with streptococcal throat infections and mainly occurs in HLA-Cw6(+) patients, the specific immunologic response to this innate stimulus that causes these skin lesions is poorly understood. OBJECTIVE: This study aims to elucidate how key cellular elements of patients with GP respond to Streptococcus pyogenes and whether this initial immune response is favored by the genetic and environmental background of these patients. METHODS: Circulating memory T cells and autologous epidermal cells from samples from either patients with GP (n = 14) or healthy control subjects (n = 6) were cocultured ex vivo in the presence of an S pyogenes extract. Levels of the psoriasis-associated cytokines IL-17A, IL-17F, IFN-γ, TNF-α, IL-6, and IL-8 were determined. The expression of several genes with increased (DEFB4, S100A7, LCN2, IL36G, IL8, CXCL9, CXCL10, and CXCL11) or decreased (FLG and LOR) transcripts in psoriatic lesions was examined in keratinocytes treated with coculture supernatants. RESULTS: When skin-homing effector memory cutaneous lymphocyte antigen-positive T cells were used in cocultures, a TH17-dominant response was observed, as reflected by the higher amounts of IL-17A and IL-17F than IFN-γ. Moreover, a higher TH17 response was observed in cells isolated from patients with flares associated with a streptococcal tonsillitis and with the HLA-Cw6 allele (cohort 1). In addition, in normal keratinocytes the supernatants from these cocultures induced an increase in IL-17-associated genes, such as DEFB4, S100A7, LCN2, IL36G, and IL8 but a decrease in FLG and LOR, thereby confirming the role of activated TH17 cells. CONCLUSION: This study reveals a dominant TH17 response of cutaneous lymphocyte antigen-positive T cells activated by epidermal cells and S pyogenes in patients with GP.

Circulating CLA+ T lymphocytes as peripheral cell biomarkers in T-cell-mediated skin diseases.

T lymphocytes expressing the CLA antigen constitute a subset of effector memory lymphocytes that are functionally involved in T-cell-mediated cutaneous diseases. Skin-seeking lymphocytes recirculate between inflamed skin and blood during cutaneous inflammation. Many studies in different T-cell-mediated inflammatory cutaneous diseases have clearly related their pathologic mechanisms to CLA+ T cells. Based on common features of these cells in different cutaneous disorders mediated by T cells, we propose that circulating CLA+T cells could constitute very useful peripheral cellular biomarkers for T-cell-mediated skin diseases.

Arginine transport is impaired in C57Bl/6 mouse macrophages as a result of a deletion in the promoter of Slc7a2 (CAT2), and susceptibility to Leishmania infection is reduced.

Host genetic factors play a crucial role in immune response. To determine whether the differences between C57Bl/6 and BALB-C mice are due only to the production of cytokines by T-helper 1 cells or T-helper 2 cells, we obtained bone marrow-derived macrophages from both strains and incubated them with these cytokines. Although the induction of Nos2 and Arg1 was similar in the 2 strains, infectivity to Leishmania major differed, as did macrophage uptake of arginine, which was higher in BALB-C macrophages. The levels of interferon γ- and interleukin 4-dependent induction of the cationic amino acid transporter SLC7A2 (also known as "cationic amino acid transporter 2," or "CAT2") were decreased in macrophages from C57Bl/6 mice. This reduction was a result of a deletion in the promoter of one of the 4 AGGG repeats. These results demonstrate that the availability of arginine controls critical aspects of macrophage activation and reveal a factor for susceptibility to Leishmania infection.

Streptococcus induces circulating CLA(+) memory T-cell-dependent epidermal cell activation in psoriasis.

Streptococcal throat infection is associated with a specific variant of psoriasis and with HLA-Cw6 expression. In this study, activation of circulating psoriatic cutaneous lymphocyte-associated antigen (CLA)(+) memory T cells cultured together with epidermal cells occurred only when streptococcal throat extracts were added. This triggered the production of Th1, Th17, and Th22 cytokines, as well as epidermal cell mediators (CXCL8, CXCL9, CXCL10, and CXCL11). Streptococcal extracts (SEs) did not induce any activation with either CLA(-) cells or memory T cells cultured together with epidermal cells from healthy subjects. Intradermal injection of activated culture supernatants into mouse skin induced epidermal hyperplasia. SEs also induced activation when we used epidermal cells from nonlesional skin of psoriatic patients with CLA(+) memory T cells. Significant correlations were found between SE induced upregulation of mRNA expression for ifn-γ, il-17, il-22, ip-10, and serum level of antistreptolysin O in psoriatic patients. This study demonstrates the direct involvement of streptococcal infection in pathological mechanisms of psoriasis, such as IL-17 production and epidermal cell activation.

Macrophage proinflammatory activation and deactivation: a question of balance.

Macrophages play key roles in inflammation. During the onset of the inflammatory process, these phagocytic cells become activated and have destructive effects. Macrophage activation, which involves the induction of more than 400 genes, results in an increased capacity to eliminate bacteria and to regulate many other cells through the release of cytokines and chemokines. However, excessive activation has damaging effects, such as septic shock, which can lead to multiple organ dysfunction syndrome and death. In other situations, persistence of proinflammatory activity results in the development of chronic inflammation, such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease. To prevent undesirable effects, several mechanisms have evolved to control the excess of activation, thereby leading to macrophage deactivation and the resolution of inflammation. In this review, we discuss several mechanisms that mediate macrophage deactivation.

Pathological mechanisms of skin homing T cells in atopic dermatitis.

Skin infiltration of circulating memory T cells with cutaneous tropism is considered one of the pathologic mechanisms in atopic dermatitis (AD). Skin-seeking circulating T lymphocytes can be identified by their expression of the cutaneous lymphocyte-associated antigen on the cell surface. Recent studies have contributed useful new information about the function and recirculation properties of those cells in AD patients. This review integrates the latest findings on peripheral cutaneous lymphocyte-associated antigen memory T cells in AD and highlights the relevance of this cell type and its importance to our understanding of the pathologic mechanisms of AD.

Circulating CLA+ T cell subsets inversely correlate with disease severity and extension in acute psoriasis but not in chronic plaque psoriasis.

Circulating CLA+ T cells represent a subset of lymphocytes functionally associated to several cutaneous diseases. This population of peripheral lymphocytes is poorly characterized in acute stage psoriasis. We studied, by flow cytometry, the relationship between disease severity and extension and different subsets of circulating T cells in 31 psoriatic patients (7 guttate, 8 acute and 16 chronic psoriasis). An inverse correlation between circulating CLA+ CD3+/CD4+ subsets and disease severity and extension was found in the acute form of psoriasis. Interestingly, we also observed that circulating CLA+CD4+CD25+ cells inversely correlated with PASI and BSA in guttate patients, which had not been shown previously. These results may contribute to clarify the role of circulating T cells in psoriasis, especially in early stages of psoriasis.