T-Cell Adhesion in Healthy and Inflamed Skin

Integration of genetic and chromatin modification data pinpoints autoimmune-specific remodeling of enhancer landscape in CD4+ T cells

CD4+ T cells play a crucial role in adaptive immune responses and have been implicated in the pathogenesis of autoimmune diseases (ADs). Despite numerous studies, the molecular mechanisms underlying T cell dysregulation in ADs remain incompletely understood. Here, we used chromatin immunoprecipitation (ChIP)-sequencing of active chromatin and transcriptomic data from CD4+ T cells of healthy donors and patients with systemic lupus erythematosus (SLE), psoriasis, juvenile idiopathic arthritis (JIA), and Graves' disease to investigate the role of enhancers in AD pathogenesis. By generating enhancer-based gene regulatory networks (eGRNs), we identified disease-specific dysregulated pathways and potential downstream target genes of enhancers harboring AD-associated single-nucleotide polymorphisms (SNPs), which we also validated using chromatin-capture (HiC) data and CRISPR interference (CRISPRi) in primary CD4+ T cells. Our results suggest that alterations in the regulatory landscapes of CD4+ T cells, including enhancers, contribute to the development of ADs and provide a basis for developing new therapeutic approaches.

The protective roles of integrin α4β7 and Amphiregulin-expressing innate lymphoid cells in lupus nephritis

Type 2 innate lymphoid cells (ILC2s) have emerged as key regulators of the immune response in renal inflammatory diseases such as lupus nephritis. However, the mechanisms underlying ILC2 adhesion and migration in the kidney remain poorly understood. Here, we revealed the critical role of integrin α4β7 in mediating renal ILC2 adhesion and function. We found that integrin α4β7 enables the retention of ILC2s in the kidney by binding to VCAM-1, E-cadherin, or fibronectin on structural cells. Moreover, integrin α4β7 knockdown reduced the production of the reparative cytokine amphiregulin (Areg) by ILC2s. In lupus nephritis, TLR7/9 signaling within the kidney microenvironment downregulates integrin α4β7 expression, leading to decreased Areg production and promoting the egress of ILC2s. Notably, IL-33 treatment upregulated integrin α4β7 and Areg expression in ILC2s, thereby enhancing survival and reducing inflammation in lupus nephritis. Together, these findings highlight the potential of targeting ILC2 adhesion as a therapeutic strategy for autoimmune kidney diseases.

Heterogeneity and plasticity of tissue-resident memory T cells in skin diseases and homeostasis: a review

Skin tissue-resident memory T (Trm) cells are produced by antigenic stimulation and remain in the skin for a long time without entering the peripheral circulation. In the healthy state Trm cells can play a patrolling and surveillance role, but in the disease state Trm cells differentiate into various phenotypes associated with different diseases, exhibit different localizations, and consequently have local protective or pathogenic roles, such as disease recurrence in vitiligo and maintenance of immune homeostasis in melanoma. The most common surface marker of Trm cells is CD69/CD103. However, the plasticity of tissue-resident memory T cells after colonization remains somewhat uncertain. This ambiguity is largely due to the variation in the functionality and ultimate destination of Trm cells produced from memory cells differentiated from diverse precursors. Notably, the presence of Trm cells is not stationary across numerous non-lymphoid tissues, most notably in the skin. These cells may reenter the blood and distant tissue sites during the recall response, revealing the recycling and migration potential of the Trm cell progeny. This review focuses on the origin and function of skin Trm cells, and provides new insights into the role of skin Trm cells in the treatment of autoimmune skin diseases, infectious skin diseases, and tumors.

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.

Effect of Mixed Probiotics on Ovalbumin-Induced Atopic Dermatitis in Juvenile Mice

Atopic dermatitis is one of the most common dermatologic problems, especially in children. Given the ability of symbiotic microorganisms in modulating the immune system, probiotics administration has been studied in previous research in the management of atopic dermatitis. However, there are conflicting results between studies. In this study, we aimed to assess the effectiveness of mixed probiotics as a treatment option for atopic dermatitis induced by ovalbumin. BALB/c juvenile mice were classified and divided into the ovalbumin group, mixed probiotic group (ovalbumin + LK), and control group. Except for the control group, all mice were sensitized with ovalbumin to establish a model of atopic dermatitis. The mixed probiotics were given by gavage for 14 days. Mice body weight, skin lesions, skin inflammation, ovalbumin-specific Ig, the number of Treg and CD103+DC, and the expression level of PD-1/PD-L1 were examined. The results showed that mixed probiotics can improve body weight and alleviate skin symptoms. Mixed probiotics reduced serum Th2 inflammatory factors, eosinophils, mast cell degranulation, mast cell count, and the expression of ovalbumin-specific immunoglobulin E/G1 and increased the anti-inflammatory cytokine interleukin-10, Treg cells, CD103+DC cells, and the expression level of PD-1/PD-L1. These findings suggest that mixed probiotics could be a viable treatment option for atopic dermatitis and provide insight into the underlying mechanisms involved.

ABCC1, ABCG2 and FOXP3: Predictive Biomarkers of Toxicity from Methotrexate Treatment in Patients Diagnosed with Moderate-to-Severe Psoriasis

BACKGROUND

Methotrexate (MTX) is one of the most extensively used drugs in the treatment of moderate-to-severe psoriasis (PS). However, it frequently must be suspended owing to the toxicity in certain patients.

OBJECTIVE

To evaluate the influence of ABCC1, ABCG2, and FOXP3 in the development of MTX toxicity in PS.

METHODS

Retrospective cohort study with 101 patients. Five single-nucleotide polymorphisms (SNPs) were genotyped using real-time polymerase chain reaction with TaqMan probes.

RESULTS

Patients carrying ABCC1 rs2238476-AG genotype (AG vs. GG: OR = 8.04; 95% CI = 1.48-46.78; p = 0.015); FOXP3 rs376154-GT and GG genotypes (GT vs. TT/GG: OR = 3.86; 95% CI = 1.17-13.92; p = 0.031) and ABCG2 rs13120400-T allele (T vs. CC: OR = 8.33; 95% CI = 1.24-164.79; p = 0.059) showed a higher risk of developing more than one adverse effect. The toxicity analysis by subtypes showed that the ABCC1 rs2238476-AG genotype (AG vs. GG: OR = 8.10; 95% CI = 1.69-46.63; p = 0.011) and FOXP3 rs376154-GT genotype (OR = 4.11; 95% CI = 1.22-15.30; p = 0.027) were associated with the appearance of asthenia. No association of the other ABCC1 polymorphisms (rs35592 and rs246240) with MTX toxicity was found.

CONCLUSION

ABCC1, ABCG2, and FOXP3 polymorphisms can be considered to be risk biomarkers of toxicities in PS patients treated with MTX.

CD103 Regulates Dermal Regulatory T Cell Motility and Interactions with CD11c-Expressing Leukocytes to Control Skin Inflammation

Dermal regulatory T cells (Tregs) are essential for maintenance of skin homeostasis and control of skin inflammatory responses. In mice, Tregs in the skin are characterized by high expression of CD103, the αE integrin. Evidence indicates that CD103 promotes Treg retention within the skin, although the mechanism underlying this effect is unknown. The main ligand of CD103, E-cadherin, is predominantly expressed by cells in the epidermis. However, because Tregs are predominantly located within the dermis, the nature of the interactions between E-cadherin and CD103-expressing Tregs is unclear. In this study, we used multiphoton intravital microscopy to examine the contribution of CD103 to Treg behavior in resting and inflamed skin of mice undergoing oxazolone-induced contact hypersensitivity. Inhibition of CD103 in uninflamed skin did not alter Treg behavior, whereas 48 h after inducing contact hypersensitivity by oxazolone challenge, CD103 inhibition increased Treg migration. This coincided with E-cadherin upregulation on infiltrating myeloid leukocytes in the dermis. Using CD11c-enhanced yellow fluorescent protein (EYFP) × Foxp3-GFP dual-reporter mice, inhibition of CD103 was found to reduce Treg interactions with dermal dendritic cells. CD103 inhibition also resulted in increased recruitment of effector CD4+ T cells and IFN-γ expression in challenged skin and resulted in reduced glucocorticoid-induced TNFR-related protein expression on Tregs. These results demonstrate that CD103 controls intradermal Treg migration, but only at later stages in the inflammatory response, when E-cadherin expression in the dermis is increased, and provide evidence that CD103-mediated interactions between Tregs and dermal dendritic cells support regulation of skin inflammation.

Differential Homing Receptor Profiles of Lymphocytes Induced by Attenuated versus Live Plasmodium falciparum Sporozoites

The onset of an adaptive immune response provides the signals required for differentiation of antigen-specific lymphocytes into effector cells and imprinting of these cells for re-circulation to the most appropriate anatomical site (i.e., homing). Lymphocyte homing is governed by the expression of tissue-specific lymphocyte homing receptors that bind to unique tissue-specific ligands on endothelial cells. In this study, a whole-parasite malaria vaccine (radiation-attenuated sporozoites (RAS)) was used as a model system to establish homing receptor signatures induced by the parasite delivered through mosquito bite to provide a benchmark of desirable homing receptors for malaria vaccine developers. This immunization regimen resulted in the priming of antigen-specific B cells and CD8⁺ T cells for homing primarily to the skin and T/B cell compartments of secondary lymphoid organs. Infection with live sporozoites, however, triggers the upregulation of homing receptor for the liver and the skin, demonstrating that there is a difference in the signal provided by attenuated vs. live sporozoites. This is the first report on imprinting of homing routes by Plasmodium sporozoites and, surprisingly, it also points to additional, yet to be identified, signals provided by live parasites that prime lymphocytes for homing to the liver. The data also demonstrate the utility of this method for assessing the potential of vaccine formulations to direct antigen-specific lymphocytes to the most relevant anatomical site, thus potentially impacting vaccine efficacy.

Regulation and dysregulation of hair regeneration: aiming for clinical application

Hair growth and regeneration represents a remarkable example of stem cell function. Recent progress emphasizes the micro- and macro- environment that controls the regeneration process. There is a shift from a stem cell-centered view toward the various layers of regulatory mechanisms that control hair regeneration, which include local growth factors, immune and neuroendocrine signals, and dietary and environmental factors. This is better suited for clinical application in multiple forms of hair disorders: in male pattern hair loss, the stem cells are largely preserved, but androgen signaling diminishes hair growth; in alopecia areata, an immune attack is targeted toward the growing hair follicle without abrogating its regeneration capability. Genome-wide association studies further revealed the genetic bases of these disorders, although the precise pathological mechanisms of the identified loci remain largely unknown. By analyzing the dysregulation of hair regeneration under pathological conditions, we can better address the complex interactions among stem cells, the differentiated progeny, and mesenchymal components, and highlight the critical role of macroenvironment adjustment that is essential for hair growth and regeneration. The poly-genetic origin of these disorders makes the study of hair regeneration an interesting and challenging field.

Mechanosurveillance: Tiptoeing T Cells

Efficient scanning of tissue that T cells encounter during their migratory life is pivotal to protective adaptive immunity. In fact, T cells can detect even a single antigenic peptide/MHC complex (pMHC) among thousands of structurally similar yet non-stimulatory endogenous pMHCs on the surface of antigen-presenting cells (APCs) or target cells. Of note, the glycocalyx of target cells, being composed of proteoglycans and bulky proteins, is bound to affect and even modulate antigen recognition by posing as a physical barrier. T cell-resident microvilli are actin-rich membrane protrusions that puncture through such barriers and thereby actively place the considerably smaller T-cell antigen receptors (TCRs) in close enough proximity to APC-presented pMHCs so that productive interactions may occur efficiently yet under force. We here review our current understanding of how the plasticity of T-cell microvilli and physicochemical properties of the glycocalyx may affect early events in T-cell activation. We assess insights gained from studies on T-cell plasma membrane ultrastructure and provide an update on current efforts to integrate biophysical aspects such as the amplitude and directionality of TCR-imposed mechanical forces and the distribution and lateral mobility of plasma membrane-resident signaling molecules into a more comprehensive view on sensitized T-cell antigen recognition.

Transforming growth factor-β1 in regulatory T cell biology

Transforming growth factor-β1 (TGF-β1) is inextricably linked to regulatory T cell (Treg) biology. However, precisely untangling the role for TGF-β1 in Treg differentiation and function is complicated by the pleiotropic and context-dependent activity of this cytokine and the multifaceted biology of Tregs. Among CD4+ T cells, Tregs are the major producers of latent TGF-β1 and are uniquely able to activate this cytokine via expression of cell surface docking receptor glycoprotein A repetitions predominant (GARP) and αv integrins. Although a preponderance of evidence indicates no essential roles for Treg-derived TGF-β1 in Treg immunosuppression, TGF-β1 signaling is crucial for Treg development in the thymus and periphery. Furthermore, active TGF-β1 instructs the differentiation of other T cell subsets, including TH17 cells. Here, we will review TGF-β1 signaling in Treg development and function and discuss knowledge gaps, future research, and the TGF-β1/Treg axis in the context of cancer immunotherapy and fibrosis.