CD1a function in human skin disease

Functional and biological implications of clonotypic diversity among human donor-unrestricted T cells

T cells express a T-cell receptor (TCR) heterodimer that is the product of germline rearrangement and junctional editing resulting in immense clonotypic diversity. The generation of diverse TCR repertoires enables the recognition of pathogen-derived peptide antigens presented by polymorphic major histocompatibility complex (MHC) molecules. However, T cells also recognize nonpeptide antigens through nearly monomorphic antigen-presenting systems, such as cluster of differentiation 1 (CD1), MHC-related protein 1 (MR1) and butyrophilins (BTNs). This potential for shared immune responses across genetically diverse populations led to their designation as donor-unrestricted T cells (DURTs). As might be expected, some CD1-, MR1- and BTN-restricted T cells express a TCR that is conserved across unrelated individuals. However, several recent studies have reported unexpected diversity among DURT TCRs, and increasing evidence suggests that this diversity has functional consequences. Recent reports also challenge the dogma that immune cells are either innate or adaptive and suggest that DURT TCRs may act in both capacities. Here, we review this evidence and propose an expanded view of the role for clonotypic diversity among DURTs in humans, including new perspectives on how DURT TCRs may integrate their adaptive and innate immune functions.

Protein Haptenation and Its Role in Allergy

Humans are exposed to numerous electrophilic chemicals either as medicines, in the workplace, in nature, or through use of many common cosmetic and household products. Covalent modification of human proteins by such chemicals, or protein haptenation, is a common occurrence in cells and may result in generation of antigenic species, leading to development of hypersensitivity reactions. Ranging in severity of symptoms from local cutaneous reactions and rhinitis to potentially life-threatening anaphylaxis and severe hypersensitivity reactions such as Stephen-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), all these reactions have the same Molecular Initiating Event (MIE), i.e. haptenation. However, not all individuals who are exposed to electrophilic chemicals develop symptoms of hypersensitivity. In the present review, we examine common chemistry behind the haptenation reactions leading to formation of neoantigens. We explore simple reactions involving single molecule additions to a nucleophilic side chain of proteins and complex reactions involving multiple electrophilic centers on a single molecule or involving more than one electrophilic molecule as well as the generation of reactive molecules from the interaction with cellular detoxification mechanisms. Besides generation of antigenic species and enabling activation of the immune system, we explore additional events which result directly from the presence of electrophilic chemicals in cells, including activation of key defense mechanisms and immediate consequences of those reactions, and explore their potential effects. We discuss the factors that work in concert with haptenation leading to the development of hypersensitivity reactions and those that may act to prevent it from developing. We also review the potential harnessing of the specificity of haptenation in the design of potent covalent therapeutic inhibitors.

Integrated Analysis of CD1A Immune Infiltration and Competing Endogenous RNA Networks in COAD

Background

The CD1A gene, a key component of the human immune system and part of the CD1 family, plays a crucial role in presenting lipid antigens to T cells. Abnormal CD1A expression is associated with various immune-related diseases and tumors. However, the biological function of CD1A in COAD is unclear.

Methods

Multiple databases were systematically employed to conduct an analysis of CD1A expression in pan-cancer and COAD, along with its clinical-pathological features. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses of CD1A were performed using the 'clusterProfiler' package. The Protein-protein interaction (PPI) analysis of CD1A was used the STRING database. Additionally, TIMER and ssGSEA tools were used to explore the relationship between CD1A expression in COAD and immune cell infiltration. The study also investigated the association between CD1A expression and N6-methyladenosine (m6A) modification genes in the TCGA COAD cohort and constructed a CD1A-centric competing endogenous RNA (ceRNA) regulatory network.

Results

CD1A displays varying expression levels in various tumors, including COAD, and is closely linked to clinical-pathological characteristics. GO analysis suggests that CD1A plays a role in important processes like antigen processing and presentation, leukocyte-mediated immunity, and lymphocyte-mediated immunity. KEGG analysis identifies CD1A's involvement in key pathways such as the Chemokine signaling pathway and Cytokine-cytokine receptor interaction. PPI analysis highlights CD1A's interactions with CD207, CD1C, CD1E, FOXP3, and ITGB2. ssGSEA analysis indicates a significant relationship between CD1A expression and the infiltration of various immune cells in COAD. Significant associations were found between CD1A and m6A modification genes in COAD. Furthermore, a CD1A-centered ceRNA regulatory network has been constructed.

Conclusion

CD1A emerges as a potential biomarker for the diagnosis and treatment of COAD, showing a strong association with tumor immune infiltration, m6A modification, and the ceRNA network.

CD1a and skin T cells: a pathway for therapeutic intervention

The CD1 and MR1 protein families present lipid antigens and small molecules to T cells, complementing well-studied major histocompatibility complex-peptide mechanisms. The CD1a subtype is highly and continuously expressed within the skin, most notably on Langerhans cells, and has been demonstrated to present self and foreign lipids to T cells, highlighting its cutaneous sentinel role. Alteration of CD1a-dependent T-cell responses has recently been discovered to contribute to the pathogenesis of several inflammatory skin diseases. In this review, we overview the structure and role of CD1a and outline the current evidence implicating CD1a in the development of psoriasis, atopic dermatitis and allergic contact dermatitis.

Transcriptional differences between vesicular hand eczema and atopic dermatitis

BACKGROUND

Transcriptome analyses of vesicular hand eczema (VHE) indicated a large overlap with atopic dermatitis (AD). However, differentially expressed genes (DEGs) that differentiate VHE from AD are unknown.

OBJECTIVE

To identify distinctive transcriptional features of VHE in comparison to AD.

METHODS

We re-analysed RNA sequencing data of 10 lesional palmar VHE epidermal biopsies and performed DEG analyses. We adjusted the obtained DEG results of 57 lesional whole AD skin biopsies of the upper extremities or trunk to our criteria. Up- and down-regulated DEGs in both skin diseases, VHE-only, AD-only, and opposite regulated DEGs were identified. Enrichment analyses and Chi-squared tests were conducted to test for differences in gene set enrichment between both skin diseases.

RESULTS

Comparing 3028 DEGs in VHE (1645 up; 1383 down) with 5391 DEGs in AD (3842 up; 1549 down), revealed 1516 shared DEGs (1179 up; 337 down) and 1512 DEGs unique to VHE (466 up, 1046 down). Interferon signalling and necroptosis were significantly more prominent in VHE compared to AD. Downregulated genes identified only in VHE (like DNASE1L2, KRT2, KRT9 and KRT25) indicate an aberrant epidermal differentiation.

CONCLUSION

Our study indicates a common pathophysiology between VHE and AD, but also reveals transcriptional differences between VHE and AD.

Can we predict T cell specificity with digital biology and machine learning?

Recent advances in machine learning and experimental biology have offered breakthrough solutions to problems such as protein structure prediction that were long thought to be intractable. However, despite the pivotal role of the T cell receptor (TCR) in orchestrating cellular immunity in health and disease, computational reconstruction of a reliable map from a TCR to its cognate antigens remains a holy grail of systems immunology. Current data sets are limited to a negligible fraction of the universe of possible TCR-ligand pairs, and performance of state-of-the-art predictive models wanes when applied beyond these known binders. In this Perspective article, we make the case for renewed and coordinated interdisciplinary effort to tackle the problem of predicting TCR-antigen specificity. We set out the general requirements of predictive models of antigen binding, highlight critical challenges and discuss how recent advances in digital biology such as single-cell technology and machine learning may provide possible solutions. Finally, we describe how predicting TCR specificity might contribute to our understanding of the broader puzzle of antigen immunogenicity.

CD1-Restricted T Cells in Inflammatory Skin Diseases

Autoimmunity results from the breaking of immune tolerance, leading to inflammation and pathology. Although well studied in the conventional T-cell field, the role of nonconventional T cells in autoimmunity is less understood. CD1-restricted T cells recognize lipid antigens rather than peptide antigens and have been implicated in various autoimmune skin conditions, including psoriasis and atopic dermatitis. In this review, we will discuss the self-lipids that CD1-restricted T cells recognize and how these T cells become aberrantly regulated in pathogenic skin conditions.

In Vitro Monitoring of Human T Cell Responses to Skin Sensitizing Chemicals-A Systematic Review

Background: Chemical allergies are T cell-mediated diseases that often manifest in the skin as allergic contact dermatitis (ACD). To prevent ACD on a public health scale and avoid elicitation reactions at the individual patient level, predictive and diagnostic tests, respectively, are indispensable. Currently, there is no validated in vitro T cell assay available. The main bottlenecks concern the inefficient generation of T cell epitopes and the detection of rare antigen-specific T cells. Methods: Here, we systematically review original experimental research papers describing T cell activation to chemical skin sensitizers. We focus our search on studies published in the PubMed and Scopus databases on non-metallic allergens in the last 20 years. Results: We identified 37 papers, among them 32 (86%) describing antigen-specific human T cell activation to 31 different chemical allergens. The remaining studies measured the general effects of chemical allergens on T cell function (five studies, 14%). Most antigen-specific studies used peripheral blood mononuclear cells (PBMC) as antigen-presenting cells (APC, 75%) and interrogated the blood T cell pool (91%). Depending on the individual chemical properties, T cell epitopes were generated either by direct administration into the culture medium (72%), separate modification of autologous APC (29%) or by use of hapten-modified model proteins (13%). Read-outs were mainly based on proliferation (91%), often combined with cytokine secretion (53%). The analysis of T cell clones offers additional opportunities to elucidate the mechanisms of epitope formation and cross-reactivity (13%). The best researched allergen was p-phenylenediamine (PPD, 12 studies, 38%). For this and some other allergens, stronger immune responses were observed in some allergic patients (15/31 chemicals, 48%), illustrating the in vivo relevance of the identified T cells while detection limits remain challenging in many cases. Interpretation: Our results illustrate current hardships and possible solutions to monitoring T cell responses to individual chemical skin sensitizers. The provided data can guide the further development of T cell assays to unfold their full predictive and diagnostic potential, including cross-reactivity assessments.

Synergistic Effects of Korean Red Ginseng Extract and the Conventional Systemic Therapeutics of Atopic Dermatitis in a Murine Model

The synergistic effects of Korean Red ginseng (KRG, Panax ginseng C.A. Mey.) on conventional systemic therapeutics of atopic dermatitis (AD) have not been studied yet. To analyze the synergistic effects of KRG extract and the conventional systemic therapeutics of AD in TNCB-induced AD mouse model, we determined the change in modified scoring of index, the transepidermal water loss, the skin pathology, serum IgE, and the expression of various cytokines after combination treatment to the five-week-old NC/Nga female mice. The severity of AD was significantly decreased in the KRG + hydroxyzine (AH) group than AH group, and in the KRG + evening primrose oil (EPO) group than EPO group. A significant decrease in dermal inflammation was observed in the KRG + AH group than that in the AH group, and in the KRG + EPO group than that in the EPO group (p = 0.008), respectively. A decrease in CD1a expression was observed in the KRG + AH group when compared to the AH group (p = 0.008), and KRG + EPO group when compared to the EPO group. Compared to the CS group, the KRG + CS group showed a significant decrease in IL-17 expression. A combination of KRG and conventional systemic therapeutics can safely and effectively manage the AD.

Does CD1a Expression Influence T Cell Function in Patients With Langerhans Cell Histiocytosis?

Langerhans cell histiocytosis lesions are characterized by CD1a+ myeloid lineage LCH cells and an inflammatory infiltrate of cytokines and immune cells, including T cells. T cells that recognize CD1a may be implicated in the pathology of many disease states including cancer and autoimmunity but have not been studied in the context of LCH despite the expression of CD1a by LCH cells. In this perspective article, we discuss the expression of CD1a by LCH cells, and we explore the potential for T cells that recognize CD1a to be involved in LCH pathogenesis.

Role of Group 1 CD1-Restricted T Cells in Host Defense and Inflammatory Diseases

Group 1 CD1-restricted T cells are members of the unconventional T cell family that recognize lipid antigens presented by CD1a, CD1b, and CD1c molecules. Although they developmentally mirror invariant natural killer T cells, they have diverse antigen specificity and functional capacity, with both anti-microbial and autoreactive targets. The role of group 1 CD1-restricted T cells has been best established in Mycobacterium tuberculosis (Mtb) infection in which a wide variety of lipid antigens have been identified and their ability to confer protection against Mtb infection in a CD1 transgenic mouse model has been shown. Group 1 CD1-restricted T cells have also been implicated in other infections, inflammatory conditions, and malignancies. In particular, autoreactive group 1 CD1-restricted T cells have been shown to play a role in several skin inflammatory conditions. The prevalence of group 1 CD1 autoreactive T cells in healthy individuals suggests the presence of regulatory mechanisms to suppress autoreactivity in homeostasis. The more recent use of group 1 CD1 tetramers and mouse models has allowed for better characterization of their phenotype, functional capacity, and underlying mechanisms of antigen-specific and autoreactive activation. These discoveries may pave the way for the development of novel vaccines and immunotherapies that target group 1 CD1-restricted T cells.