Proteins in the Skin and Blood in Patients with Psoriasis: A Systematic Review of Proteomic Studies.

BACKGROUND: Proteins play a central role in psoriasis as they are involved in the structural phenotypic changes and inflammation that characterize the disease. This systematic review aimed to assess which proteins have been consistently reported as upregulated or downregulated in the skin and blood from patients with psoriasis. METHODS: We included proteomic studies reporting differentially expressed proteins (DEPs) in at least one of four predefined comparisons using a standardized procedure to extract and align data. Network analysis of functional protein associations was made with StringApp in Cytoscape. A protocol for this review was registered in the PROSPERO database (ref:CRD42022363226). RESULTS: We identified and assessed 772 studies published between December 2, 1996, and April 28, 2023, among which 30 studies met the inclusion and data availability criteria for analysis that together reported a sum of 5,314 DEPs. The majority of consistently reported upregulated and downregulated proteins were found in lesional versus non-lesional skin (n = 313), followed by lesional versus healthy skin (n = 185), blood from patients with psoriasis versus blood from healthy individuals (n = 140), and non-lesional versus healthy skin (n = 1). Network analysis of upregulated proteins revealed different functional clusters with interleukin (IL)-6, IL-8, IL-17A, C-C motif chemokine (CCL) 20, signal transducer and activator of transcription (STAT) 3, and interferon (IFN)-γ along with less well-studied proteins playing central roles. Some of the reported changes are associated with anti-inflammatory effects. Additionally, the proteomic dysregulation also included antimicrobial peptides, alarmins, angiogenic factors, and proteins related to protein synthesis. CONCLUSION: Our findings generally support current understandings of the pathological mechanisms in psoriasis. Importantly, some consistent findings have not been discussed before and deserve attention in future research.

LAG3 and TIGIT Expression on Tumor-Infiltrating Lymphocytes in Cutaneous Melanoma.

BACKGROUND: Melanoma is widely recognized to be an immunogenic tumor that often contains tumor-infiltrating lymphocytes (TILs) in the tumor microenvironment. During cancer progression, expression of ligands that bind immune checkpoint (IC) proteins, such as PD-1, expressed on the surface of TILs, hinder them from exerting their antitumor functions. TILs consist of a heterogenous group of immune cells and their presence is associated with an improved overall survival in melanoma patients. Introduction of IC inhibitors has revolutionized management and prognosis of advanced melanoma. Unfortunately, the response rates have continued to be limited, resulting in growing interest in characterizing novel IC proteins, and developing combination therapy that includes inhibitors against multiple IC proteins. METHODS: In a regional cohort of 166 patients diagnosed with cutaneous superficial spreading melanoma with different degree of TILs, we investigated the tumor immune-associated gene expression profile using NanoString Technology. We used multiplex immunofluorescence (mIF) staining in a subset of tumors (N = 7), combining IC proteins T-cell immunoglobulin and ITIM domain (TIGIT) and LAG3 with a melanoma cell marker (SOX10) and immune cell markers (CD8 [cytotoxic T cells], CD4 [T helper cells], FOXP3 [regulatory T cells/Tregs], PAX5 [B cells], and CD56 [NK/NKT cells]) and IC protein PD-1. RESULTS: We found upregulation of 91 differentially expressed genes, including IC proteins, LAG3 and TIGIT in melanomas with brisk TILs compared to tumors where TILs were absent. mIF staining revealed LAG3 and TIGIT expression in the majority of CD8+ T cells. Only few Tregs and CD4+ T cells expressed LAG3, whereas majority of them expressed TIGIT. LAG3 and TIGIT were expressed in a small fraction of the NK/NKT cells and lacked in the B cells. The majority of PD-1+ cells co-localized with LAG3 and TIGIT. CONCLUSION: We report a variable expression of LAG3 and TIGIT on TILs subtypes and a coeval occurrence with PD-1. This knowledge places LAG3 and TIGIT in spatial and cellular context in melanoma. The data suggest that targeting multiple IC proteins might help overcome the current challenges with IC therapies.

BRAFV600E Expression Is Homogenous and Associated with Nonrecurrent Disease and Better Survival in Primary Melanoma.

BACKGROUND: Superficial spreading melanomas (SSMs) are the most common type of melanoma and cause the majority of skin cancer deaths. More than 50% of cases harbor a mutation in the BRAF gene that activates the mitogen-activated protein kinase (MAPK) cancer signaling pathway. BRAFV600E is the most common BRAF mutation, and it represents an important biomarker that guides treatment selection. However, the relationship between the BRAFV600E gene expression and intratumoral protein distribution, on one side, and clinicopathological factors and patient outcomes, on the other, is not fully described. Additionally, whether MAPK cancer signaling activation in melanoma is due to increased biochemical activity of BRAFV600E, increased mRNA levels, or both requires further investigation. Here, we addressed these questions by examining expression patterns of BRAFV600E in primary treatment-naive melanomas and correlating them to clinicopathological factors and patient outcomes. METHODS: In 166 SSM cases, we performed immunohistochemical staining to investigate the protein expression of BRAFV600E, and we measured BRAF mRNA levels using NanoString nCounter system. RESULTS: Ninety-seven (49%) melanomas stained positive for BRAFV600E, with nearly 100% intratumoral homogeneity observed. Positive BRAFV600E expression was significantly associated with nonrecurrent disease and was found to be an independent predictor of better prognosis in univariate and multivariable analyses. Furthermore, presence of tumor-infiltrating lymphocytes, sentinel lymph node biopsy negativity, and low Breslow thickness were all independent predictors of better prognosis. We observed no difference in the BRAF mRNA levels in BRAFV600E-negative and BRAFV600E-positive melanomas, respectively. Validation in a larger publicly available cohort confirmed that there is only a weak correlation (Spearman 0.4) between BRAFV600E mRNA and protein levels and no differences in mRNA between BRAFV600E mutated and non-mutated patients. CONCLUSION: Our findings indicated that BRAFV600E is homogeneously present throughout the whole tumor and is associated with nonrecurrent disease and better survival in primary melanoma. We also showed that BRAFV600E mutation does not result in higher transcriptional levels, suggesting that activation of the MAPK signaling pathway in BRAFV600E mutated patients can be attributed to the increased biochemical activity caused by the mutation.

Towards Precision Dermatology: Emerging Role of Proteomic Analysis of the Skin.

BACKGROUND: The skin is the largest organ in the human body and serves as a multilayered protective shield from the environment as well as a sensor and thermal regulator. However, despite its importance, many details about skin structure and function at the molecular level remain incompletely understood. Recent advances in liquid chromatography tandem mass spectrometry (LC-MS/MS) proteomics have enabled the quantification and characterization of the proteomes of a number of clinical samples, including normal and diseased skin. SUMMARY: Here, we review the current state of the art in proteomic analysis of the skin. We provide a brief overview of the technique and skin sample collection methodologies as well as a number of recent examples to illustrate the utility of this strategy for advancing a broader understanding of the pathology of diseases as well as new therapeutic options. KEY MESSAGES: Proteomic studies of healthy skin and skin diseases can identify potential molecular biomarkers for improved diagnosis and patient stratification as well as potential targets for drug development. Collectively, efforts such as the Human Skinatlas offer improved opportunities for enhancing clinical practice and patient outcomes.

Epidermal T cell subsets-Effect of age and antigen exposure in humans and mice.

BACKGROUND: Epidermal T cells play a central role in immune surveillance and in inflammatory skin diseases. Major differences in the epidermal T cell composition are found between adult humans and antigen-inexperienced laboratory mice. Whether this is due to inborn species differences, to different environmental exposures, or a combination of the two is a matter of debate. OBJECTIVES: To investigate the role of age and exposure to antigens on epidermal T cell subsets in human and mouse skin. METHODS: We isolated T cells from the epidermis from 19 infants and 26 adults, and determined the frequency of CD4+ and CD8+ αß T cells and γδ T cells by flow cytometry. In addition, we determined the epidermal T cell composition in antigen-inexperienced and antigen-experienced mice. RESULTS: We found that humans are born with very few epidermal T cells. The number increases and the composition changes with age. In antigen-inexperienced mice, the epidermal T cell composition is unaffected by age, but it is dramatically affected by antigen exposure. CONCLUSION: Taken together, we show that antigen exposure, as opposed to age, is the major factor determining the composition of epidermal T cells, suggesting that the skin of antigen-experienced mice better reflects the immunological conditions in human skin.

Rapid allergen-induced interleukin-17 and interferon-γ secretion by skin-resident memory CD8+ T cells.

BACKGROUND: Skin-resident memory T (TRM ) cells are associated with immunological memory in the skin. Whether immunological memory responses to allergens in the skin are solely localized to previously allergen-exposed sites or are present globally in the skin is not clear. Furthermore, the mechanisms whereby TRM cells induce rapid recall responses need further investigation. OBJECTIVES: To study whether contact allergens induce local and/or global memory, and to determine the mechanisms involved in memory responses in the skin. METHODS: To address these questions, we analysed responses to contact allergens in mice and humans sensitized to 2,4-dinitrofluorobenzene and nickel, respectively. RESULTS: Challenge responses in both mice and humans were dramatically increased at sites previously exposed to allergens as compared with previously unexposed sites. Importantly, the magnitude of the challenge response correlated with the epidermal accumulation of interleukin (IL)-17A-producing and interferon (IFN)-γ-producing TRM cells. Moreover, IL-17A and IFN-γ enhanced allergen-induced IL-1ß production in keratinocytes. CONCLUSIONS: We show that sensitization with contact allergens induces a strong, long-lasting local memory and a weaker, temporary global immunological memory response to the allergen that is mediated by IL-17A-producing and IFN-γ-producing CD8+ TRM cells.

Distinct molecular signatures of mild extrinsic and intrinsic atopic dermatitis.

Atopic dermatitis (AD) is a common inflammatory skin disease with underlying defects in epidermal function and immune responses. In this study, we used microarray analysis to investigate differences in gene expression in lesional skin from patients with mild extrinsic or intrinsic AD compared to skin from healthy controls and from lesional psoriasis skin. The primary aim was to identify differentially expressed genes involved in skin barrier formation and inflammation, and to compare our results with those reported for patients with moderate and severe AD. In contrast to severe AD, expression of the majority of genes associated with skin barrier formation was unchanged or upregulated in patients with mild AD compared to normal healthy skin. Among these, no significant differences in the expression of filaggrin (FLG) and loricrin at both mRNA and protein level were found in lesional skin from patients with mild AD, despite the presence of heterozygous FLG mutations in the majority of patients with mild extrinsic AD. Several inflammation-associated genes such as S100A9, MMP12, CXCL10 and CCL18 were highly expressed in lesional skin from patients with mild psoriasis and were also increased in patients with mild extrinsic and intrinsic AD similar to previous reports for severe AD. Interestingly, expression of genes involved in inflammatory responses in intrinsic AD resembled that of psoriasis more than that of extrinsic AD. Overall, differences in expression of inflammation-associated genes found among patients with mild intrinsic and extrinsic AD correlated with previous findings for patients with severe intrinsic and extrinsic AD.

Increased prevalence of lymphoid tissue inducer cells in the cerebrospinal fluid of patients with early multiple sclerosis.

BACKGROUND: Inflammatory cytokines produced by cells of the immune system are believed to play a central role in the pathogenesis of multiple sclerosis (MS). Innate lymphoid cells (ILCs) have been shown to produce and secrete a wide range of the cytokines involved in MS pathogenesis; however, a possible implication of ILCs in MS development and disease progression has not been investigated. OBJECTIVE: With this study, we aimed to clarify a potential role of ILCs in the early stages of MS. METHODS AND RESULTS: Using flow cytometry, we analysed the prevalence and phenotype of ILCs in the cerebrospinal fluid (CSF) of patients experiencing their first or second demyelinating event. We found a substantial increase in both frequency and number of ILCs, in particular the LTi subset, as compared to healthy controls. We also found an association between CSF pleocytosis and an increased frequency of LTi cells in the CSF, suggesting a favoured recruitment of blood derived LTi cells. CONCLUSION: Our data suggests a role for ILCs, and in particular the LTi subset, in the early stages of MS. This finding represents an important contribution to the understanding of early inflammation in MS, and adds new knowledge beneficial for future MS therapies.

Different cytokine profiles of skin-derived T cell cultures from patients with atopic dermatitis and psoriasis.

OBJECTIVES: To investigate differences in expression of surface markers, cytokine profiles, and presence of CD4(+)CD8(+) T cells in skin-derived T cell cultures from patients with extrinsic atopic dermatitis (AD), intrinsic AD, and psoriasis expanded in the presence of IL-2 and IL-4. MATERIAL: Skin biopsies from patients with extrinsic AD (n = 6), intrinsic AD (n = 9) and psoriasis (n = 9). METHODS: Skin-derived T cell cultures were analyzed for expression of six surface markers, 11 intracellular cytokines, and three T cell subtype signature transcription factors by flow cytometry, and secreted cytokines by multiplex. RESULTS: A different IFN-γ profile emerged between the extrinsic AD and psoriatic T cell cultures; however, there was no difference in IL-17 profile. No differences with regard to cytokine expression were found between extrinsic AD and intrinsic AD cultures; however, cutaneous lymphocyte-associated antigen was expressed by a higher percentage of CD8(+) than CD4(+) T cells in the intrinsic AD cultures. Double-positive CD4(+)CD8(+) T cells were only detected in two out of 15 AD cultures. CONCLUSION: The data suggest that IL-2 and IL-4 affects the cytokine profile during culture. Earlier findings of substantial levels of double-positive CD4(+)CD8(+) T cells in skin derived T cell cultures from AD skin was not reproduced in this study.

IL-1ß-dependent activation of dendritic epidermal T cells in contact hypersensitivity.

Substances that penetrate the skin surface can act as allergens and induce a T cell-mediated inflammatory skin disease called contact hypersensitivity (CHS). IL-17 is a key cytokine in CHS and was originally thought to be produced solely by CD4(+) T cells. However, it is now known that several cell types, including γδ T cells, can produce IL-17. In this study, we determine the role of γδ T cells, especially dendritic epidermal T cells (DETCs), in CHS. Using a well-established model for CHS in which 2,4-dinitrofluorobenzene (DNFB) is used as allergen, we found that γδ T cells are important players in CHS. Thus, more IL-17-producing DETCs appear in the skin following exposure to DNFB in wild-type mice, and DNFB-induced ear swelling is reduced by ∼50% in TCRδ(-/-) mice compared with wild-type mice. In accordance, DNFB-induced ear swelling was reduced by ∼50% in IL-17(-/-) mice. We show that DNFB triggers DETC activation and IL-1ß production in the skin and that keratinocytes produce IL-1ß when stimulated with DNFB. We find that DETCs activated in vitro by incubation with anti-CD3 and IL-1ß produce IL-17. Importantly, we demonstrate that the IL-1R antagonist anakinra significantly reduces CHS responses, as measured by decreased ear swelling, inhibition of local DETC activation, and a reduction in the number of IL-17(+) γδ T cells and DETCs in the draining lymph nodes. Taken together, we show that DETCs become activated and produce IL-17 in an IL-1ß-dependent manner during CHS, suggesting a key role for DETCs in CHS.

Laser capture microdissection followed by next-generation sequencing identifies disease-related microRNAs in psoriatic skin that reflect systemic microRNA changes in psoriasis.

Psoriasis is a systemic disease with cutaneous manifestations. MicroRNAs (miRNAs) are small non-coding RNA molecules that are differentially expressed in psoriatic skin; however, only few cell- and region-specific miRNAs have been identified in psoriatic lesions. We used laser capture microdissection (LCM) and next-generation sequencing (NGS) to study the specific miRNA expression profiles in the epidermis (Epi) and dermal inflammatory infiltrates (RD) of psoriatic skin (N = 6). We identified 24 deregulated miRNAs in the Epi and 37 deregulated miRNAs in the RD of psoriatic plaque compared with normal psoriatic skin (FCH > 2, FDR < 0.05). Interestingly, 9 of the 37 miRNAs in RD, including miR-193b and miR-223, were recently described as deregulated in circulating peripheral blood mononuclear cells (PBMCs) from patients with psoriasis. Using flow cytometry and qRT-PCR, we found that miR-193b and miR-223 were expressed in Th17 cells. In conclusion, we demonstrate that LCM combined with NGS provides a robust approach to explore the global miRNA expression in the epidermal and dermal compartments of psoriatic skin. Furthermore, our results indicate that the altered local miRNA changes seen in the RD are reflected in the circulating immune cells, suggesting that miRNAs may contribute to the pathogenesis of psoriasis.

Epicutaneous exposure to nickel induces nickel allergy in mice via a MyD88-dependent and interleukin-1-dependent pathway.

BACKGROUND: Several attempts to establish a model in mice that reflects nickel allergy in humans have been made. Most models use intradermal injection of nickel in combination with adjuvant to induce nickel allergy. However, such models poorly reflect induction of nickel allergy following long-lasting epicutaneous exposure to nickel. OBJECTIVE: To develop a mouse model reflecting nickel allergy in humans induced by epicutaneous exposure to nickel, and to investigate the mechanisms involved in such allergic responses. METHODS: Mice were exposed to NiCl2 on the dorsal side of the ears. Inflammation was evaluated by the swelling and cell infiltration of the ears. T cell responses were determined as numbers of CD4+ and CD8+ T cells in the draining lymph nodes. Localization of nickel was examined by dimethylglyoxime staining. RESULTS: Epicutaneous exposure to nickel results in prolonged localization of nickel in the epidermis, and induces nickel allergy in mice. The allergic response to nickel following epicutaneous exposure is MyD88-dependent and interleukin (IL)-1 receptor-dependent, but independent of toll-like receptor (TLR)-4. CONCLUSION: This new model for nickel allergy that reflects epicutaneous exposure to nickel in humans shows that nickel allergy is dependent on MyD88 and IL-1 receptor signalling, but independent of TLR4.

In-Depth Proteomic Map of Innate Lymphoid Cells from Healthy Human Skin and Blood.

Innate lymphoid cells (ILCs) are essential players in the skin-associated immune system, nevertheless little is known about their proteomes and proteomic diversity. In this study, we describe about 6,600 proteins constitutively expressed by ILC2s and ILC3s from healthy human skin and blood using state-of-the-art proteomics. Although the vast majority of proteins was expressed by both ILC subsets and in both compartments, the skin ILC2s and ILC3s were more distinct than their counterparts in blood. Only skin ILC3s expressed uniquely detected proteins. Our in-depth proteomic dataset allowed us to define the cluster of differentiation marker profiles of the ILC subsets, explore distribution and abundance of proteins known to have immunological functions, as well as identify subset-specific proteins that have not previously been implicated in ILC biology. Taken together, our analyses substantially expand understanding of the protein expression signatures of ILC subsets. Going forward, these proteomic datasets will serve as valuable resources for future studies of ILC biology.

Comparative Quantitative Proteomic Analysis of Melanoma Subtypes, Nevus-Associated Melanoma, and Corresponding Nevi.

A substantial part of cutaneous malignant melanomas develops from benign nevi. However, the precise molecular events driving the transformation from benign to malignant melanoma are not well-understood. We used laser microdissection and mass spectrometry to analyze the proteomes of melanoma subtypes, including superficial spreading melanomas (n = 17), nodular melanomas (n = 17), and acral melanomas (n = 15). Furthermore, we compared the proteomes of nevi cells with those of melanoma cells within the same specimens (nevus-associated melanoma (n = 14)). In total, we quantified 7935 proteins. Despite the genomic and clinical differences of the melanoma subtypes, our analysis revealed relatively similar proteomes, except for the upregulation of proteins involved in immune activation in nodular melanomas versus acral melanomas. Examining nevus-associated melanoma versus nevi, we found 1725 differentially expressed proteins (false discovery rate < 0.05). Among these proteins were 140 that overlapped with cancer hallmarks, tumor suppressors, and regulators of metabolism and cell cycle. Pathway analysis indicated aberrant activation of the phosphoinositide 3-kinase-protein kinase B-mTOR pathways and the Hippo-YAP pathway. Using a classifier, we identified six proteins capable of distinguishing melanoma from nevi samples. Our study represents a comprehensive comparative analysis of the proteome in melanoma subtypes and associated nevi, offering insights into the biological behavior of these distinct entities.

CD4(+) T cells producing interleukin (IL)-17, IL-22 and interferon-γ are major effector T cells in nickel allergy.

BACKGROUND: It has been suggested that interleukin (IL)-17 and IL-22 play important roles in the elicitation of human allergic contact dermatitis; however, the frequencies of T cell subtypes producing IL-17 and IL-22 in human allergic contact dermatitis are unknown. OBJECTIVES: To determine the frequencies of CD4(+) , CD8(+) and γδ T cells producing IL-17, IL-22 and interferon (IFN)-γ in the blood and skin from nickel-allergic patients. PATIENTS/MATERIALS/METHODS: Blood samples were collected from 14 patients and 17 controls, and analysed by flow cytometry. Biopsies were taken from 5 patients and 6 controls, and analysed by immunohistochemistry and flow cytometry of skin lymphocytes. RESULTS: We found an increased frequency of γδ T cells in the blood, but no differences in the distribution of cytokine-producing CLA(+) T cell subtypes in nickel-allergic patients as compared with controls. In nickel-allergic patients, there was massive cellular infiltration dominated by CD4(+) T cells producing IL-17, IL-22 and IFN-γ in nickel-challenged skin but not in vehicle-challenged skin. CONCLUSION: CD4(+) T cells producing IL-17, IL-22 and IFN-γ are important effector cells in the eczematous reactions of nickel-induced allergic contact dermatitis in humans.

The Proteome of Hand Eczema Assessed by Tape Stripping.

Hand eczema (HE) is a prevalent skin disease. However, the classification of HE into different subtypes remains challenging. A limited number of previous studies have employed invasive biopsy-based strategies; yet, studies of the HE proteome using noninvasive tape-stripping methodology have not been reported. In this study, we wanted to assess whether global proteomic analysis of skin tape strip samples can be used for subclassification of patients with HE. Tape strips were collected from patients with HE and healthy skin. Liquid chromatography-mass spectrometry proteomics was performed, and the global protein expression was analyzed. We identified 2,919 proteins in stratum corneum-derived skin cells from tape strip samples. Compared with healthy skin, the lesional samples from patients with HE exhibited increased expression of immune-related markers and a decreased expression of structural barrier proteins. The difference between HE subtypes was restricted to the lesional skin areas and included an increased expression of skin barrier-related proteins independently of the concurrent AD. In conclusion, we found that the noninvasive tape strip method used in combination with liquid chromatography-mass spectrometry proteomics can be used for analysis of skin protein expression in patients with HE. Thus, the method shows potential for assessing the proteomic differences between subtypes of HE and biomarker discovery.

Central memory T cells are the most effective precursors of resident memory T cells in human skin.

The circulating precursor cells that give rise to human resident memory T cells (TRM) are poorly characterized. We used an in vitro differentiation system and human skin-grafted mice to study TRM generation from circulating human memory T cell subsets. In vitro TRM differentiation was associated with functional changes, including enhanced IL-17A production and FOXP3 expression in CD4+ T cells and granzyme B production in CD8+ T cells, changes that mirrored the phenotype of T cells in healthy human skin. Effector memory T cells (TEM) had the highest conversion rate to TRM in vitro and in vivo, but central memory T cells (TCM) persisted longer in the circulation, entered the skin in larger numbers, and generated increased numbers of TRM. In summary, TCM are highly efficient precursors of human skin TRM, a feature that may underlie their known association with effective long-term immunity.

Deep Visual Proteomics defines single-cell identity and heterogeneity.

Despite the availabilty of imaging-based and mass-spectrometry-based methods for spatial proteomics, a key challenge remains connecting images with single-cell-resolution protein abundance measurements. Here, we introduce Deep Visual Proteomics (DVP), which combines artificial-intelligence-driven image analysis of cellular phenotypes with automated single-cell or single-nucleus laser microdissection and ultra-high-sensitivity mass spectrometry. DVP links protein abundance to complex cellular or subcellular phenotypes while preserving spatial context. By individually excising nuclei from cell culture, we classified distinct cell states with proteomic profiles defined by known and uncharacterized proteins. In an archived primary melanoma tissue, DVP identified spatially resolved proteome changes as normal melanocytes transition to fully invasive melanoma, revealing pathways that change in a spatial manner as cancer progresses, such as mRNA splicing dysregulation in metastatic vertical growth that coincides with reduced interferon signaling and antigen presentation. The ability of DVP to retain precise spatial proteomic information in the tissue context has implications for the molecular profiling of clinical samples.

Immunoregulatory and lipid presentation pathways are upregulated in human face transplant rejection.

BACKGROUNDRejection is the primary barrier to broader implementation of vascularized composite allografts (VCAs), including face and limb transplants. The immunologic pathways activated in face transplant rejection have not been fully characterized.METHODSUsing skin biopsies prospectively collected over 9 years from 7 face transplant patients, we studied rejection by gene expression profiling, histology, immunostaining, and T cell receptor sequencing.RESULTSGrade 1 rejection did not differ significantly from nonrejection, suggesting that it does not represent a pathologic state. In grade 2, there was a balanced upregulation of both proinflammatory T cell activation pathways and antiinflammatory checkpoint and immunomodulatory pathways, with a net result of no tissue injury. In grade 3, IFN-γ-driven inflammation, antigen-presenting cell activation, and infiltration of the skin by proliferative T cells bearing markers of antigen-specific activation and cytotoxicity tipped the balance toward tissue injury. Rejection of VCAs and solid organ transplants had both distinct and common features. VCA rejection was uniquely associated with upregulation of immunoregulatory genes, including SOCS1; induction of lipid antigen-presenting CD1 proteins; and infiltration by T cells predicted to recognize CD1b and CD1c.CONCLUSIONOur findings suggest that the distinct features of VCA rejection reflect the unique immunobiology of skin and that enhancing cutaneous immunoregulatory networks may be a useful strategy in combatting rejection.Trial registrationClinicalTrials.gov NCT01281267.FUNDINGAssistant Secretary of Defense and Health Affairs, through Reconstructive Transplant Research (W81XWH-17-1-0278, W81XWH-16-1-0647, W81XWH-16-1-0689, W81XWH-18-1-0784, W81XWH-1-810798); American Society of Transplantation's Transplantation and Immunology Research Network Fellowship Research Grant; Plastic Surgery Foundation Fellowship from the American Society of Plastic Surgeons; Novo Nordisk Foundation (NNF15OC0014092); Lundbeck Foundation; Aage Bangs Foundation; A.P. Moller Foundation for the Advancement of Medical Science; NIH UL1 RR025758.

Spatially and cell-type resolved quantitative proteomic atlas of healthy human skin.

Human skin provides both physical integrity and immunological protection from the external environment using functionally distinct layers, cell types and extracellular matrix. Despite its central role in human health and disease, the constituent proteins of skin have not been systematically characterized. Here, we combine advanced tissue dissection methods, flow cytometry and state-of-the-art proteomics to describe a spatially-resolved quantitative proteomic atlas of human skin. We quantify 10,701 proteins as a function of their spatial location and cellular origin. The resulting protein atlas and our initial data analyses demonstrate the value of proteomics for understanding cell-type diversity within the skin. We describe the quantitative distribution of structural proteins, known and previously undescribed proteins specific to cellular subsets and those with specialized immunological functions such as cytokines and chemokines. We anticipate that this proteomic atlas of human skin will become an essential community resource for basic and translational research ( https://skin.science/ ).