Ikjot Sidhu

Atopic diseases associated with allergens, as well as allergic diseases, frequently arise early in life; however, the age-dependent mechanisms governing immune responses to allergens remain poorly understood¹. Here we find that in early life, exposure to common allergens triggers a distinct bifurcated immune response, simultaneously triggering type 17 inflammation in the skin and initiating canonical T helper 2 sensitization in the lymph nodes. This early-life γδ type 17-mediated dermatitis primes the exaggerated allergic lung inflammation upon secondary allergen exposure. Mechanistically, we find dendritic cell (DC)-mediated type 17 activation directly in the skin without requiring migration to lymph nodes; we term this state ‘peripheral immune inducer’ (pii) DC. CD301b⁺ conventional type 2 DCs acquire allergen, adopt the pii-DC state, produce IL-23 and activate local γδ type 17 cells independently of lymph-node engagement. The pii-DC state is enabled by the immature hypothalamic–pituitary–adrenal axis and physiologically low systemic glucocorticoids characteristic of early life^2,3; DC-specific deletion of the glucocorticoid receptor recapitulates the pii-DC phenotype. These findings define a developmental checkpoint, set by neuroendocrine maturation, that enables in situ DC activation and immune induction, thereby shaping age-dependent responses to allergens.

ISG15 deficiency is a type I interferonopathy characterized by elevated circulating type I interferon (IFN-I), intracranial calcifications, fibrotic skin lesions, and occasionally inflammatory lung disease. However, the mechanisms driving immune-mediated fibrosis remain poorly understood. In this study, we combined molecular biology approaches with spatial transcriptomics in ex vivo patient samples and in vitro models to characterize a novel loss-of-function ISG15 variant and to elucidate disease-associated molecular pathways. Analysis of patient skin biopsies revealed increased IFN-I–dependent apoptosis, altered macrophage polarization, enhanced epithelial-to-mesenchymal transition (EMT), and myofibroblast activation. In vitro, ISG15 knockout (KO), but not wild-type (WT), epithelial cells were predisposed to EMT following combined TGF-β and IFN-I stimulation. Additionally, ISG15 KO fibroblasts displayed impaired mechanical wound healing and increased IFN-I–induced apoptosis compared with WT cells. Collectively, our findings suggest that chronic IFN-I exposure in ISG15 deficiency disrupts wound repair, skews macrophage activation, and promotes EMT, contributing to fibrosis across multiple organ systems.

Pathogens have evolved to be highly adapted to their natural host. Community-associated methicillin-resistant Staphylococcus aureus USA300, for instance, is a lineage responsible for the epidemic of skin and soft tissue infections (SSTIs) in humans. Owing to its human tropism, mechanisms that enabled the rise of USA300 as a major skin pathogen remain incompletely defined. By leveraging a rodent-adapted strain of S. aureus , we developed a natural model of SSTIs. We found that LukMF′, a pore-forming leukocidin homolog to the human-specific LukSF-PV toxin, drives skin pathology in mice. LukMF′ lyses neutrophils via the chemokine receptor CCR1, which in turn fuels inflammatory pathology and microbial survival within the infectious nidus. Ablation of CCR1, depletion of neutrophils, or vaccination with LukMF′ all protected mice from skin pathology. Thus, these data support epidemiological studies linking leukocidins with human SSTIs and highlight the power of natural models to unearth potential targets to curtail infections.

Pathogenic CD4 T cells drive autoimmunity in diseases such as multiple sclerosis (MS) and inflammatory bowel disease (IBD). Through a forward genetic screen, we identified chloride nucleotide-sensitive channel 1A (CLNS1A) as a key regulator of inflammation in the experimental autoimmune encephalomyelitis (EAE) model of MS. CLNS1A is expressed in several subsets of CD4 T cells, including pathogenic T helper 17 (pT _H 17) cells. Deletion of Clns1a in T cells resulted in DNA damage, cell cycle arrest, impaired T cell proliferation, and effector function, thereby protecting mice from both EAE and IBD. We found that CLNS1A interacts with protein arginine methyl transferase 5 (PRMT5). Moreover, CLNS1A regulates symmetric histone dimethylation and the expression of genes involved in DNA repair, replication, and cell cycle progression. Thus, CLNS1A plays an important role in CD4 T cells by promoting genome stability and cell cycle progression.

Modulating mechanotransduction by inhibiting yes-associated protein (YAP) in mice yields wound regeneration without scarring. However, rodents are loose-skinned and fail to recapitulate key aspects of human wound repair. We sought to elucidate the effects of YAP inhibition in red Duroc pig wounds, the most human-like model of scarring. We show that one-time treatment with verteporfin, a YAP inhibitor, immediately after wounding is sufficient to prevent scarring and to drive wound regeneration in pigs. By performing single-cell RNA sequencing (scRNA-seq) on porcine wounds in conjunction with spatial proteomic analysis, we found perturbations in fibroblast dynamics with verteporfin treatment and the presence of putative pro-regenerative/profibrotic fibroblasts enriched in regenerating/scarring pig wounds, respectively. We also identified differences in enriched myeloid cell subpopulations after treatment and linked this observation to increased elaboration of interleukin-33 (IL-33) in regenerating wounds. Finally, we validated our findings in a xenograft wound model containing human neonatal foreskin engrafted onto nude mice and used scRNA-seq of human wound cells to draw parallels with fibroblast subpopulation dynamics in porcine wounds. Collectively, our findings provide support for the clinical translation of local mechanotransduction inhibitors to prevent human skin scarring, and they clarify a YAP/IL-33 signaling axis in large animal wound regeneration.

Whereas the cellular and molecular features of human inflammatory skin diseases are well characterized, their tissue context and systemic impact remain poorly understood. We thus profiled human psoriasis (PsO) as a prototypic immune-mediated condition with a high predilection for extracutaneous involvement. Spatial transcriptomics (ST) analyses of 25 healthy, active lesion, and clinically uninvolved skin biopsies and integration with public single-cell transcriptomics data revealed marked differences in immune microniches between healthy and inflamed skin. Tissue-scale cartography further identified core disease features across all active lesions, including the emergence of an inflamed suprabasal epidermal state and the presence of B lymphocytes in lesional skin. Both lesional and distal nonlesional samples were stratified by skin disease severity and not by the presence of systemic disease. This segregation was driven by macrophage-, fibroblast-, and lymphatic-enriched spatial regions with gene signatures associated with metabolic dysfunction. Together, these findings suggest that mild and severe forms of PsO have distinct molecular features and that severe PsO may profoundly alter the cellular and metabolic composition of distal unaffected skin sites. In addition, our study provides a valuable resource for the research community to study spatial gene organization of healthy and inflamed human skin.

T cell activation and function depend on Ca ²⁺ signals mediated by store-operated Ca ²⁺ entry (SOCE) through Ca ²⁺ release–activated Ca ²⁺ (CRAC) channels formed by ORAI1 proteins. We here investigated how SOCE controls T cell function in pulmonary inflammation during a T helper 1 (T _H 1) cell–mediated response to influenza A virus (IAV) infection and T _H 2 cell–mediated allergic airway inflammation. T cell–specific deletion of Orai1 did not exacerbate pulmonary inflammation and viral burdens following IAV infection but protected mice from house dust mite–induced allergic airway inflammation. ORAI1 controlled the expression of genes including p53 and E2F transcription factors that regulate the cell cycle in T _H 2 cells in response to allergen stimulation and the expression of transcription factors and cytokines that regulate T _H 2 cell function. Systemic application of a CRAC channel blocker suppressed allergic airway inflammation without compromising immunity to IAV infection, suggesting that inhibition of SOCE is a potential treatment for allergic airway disease.