Tertiary lymphoid structures sustain cutaneous B cell activity in hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic skin condition affecting approximately 1% of the US population. HS skin lesions are highly inflammatory and characterized by a large immune infiltrate. While B cells and plasma cells comprise a major component of this immune milieu, the biology and the contribution of these cells in HS pathogenesis are unclear. We aimed to investigate the dynamics and microenvironmental interactions of B cells within cutaneous HS lesions. Combining histological analysis, single-cell RNA sequencing, and spatial transcriptomics profiling of HS lesions, we defined the tissue microenvironment relative to B cell activity within this disease. Our findings identified tertiary lymphoid structures (TLSs) within HS lesions and described organized interactions among T cells, B cells, antigen-presenting cells, and skin stroma. We found evidence that B cells within HS TLSs actively underwent maturation, including participation in germinal center reactions and class switch recombination. Moreover, skin stroma and accumulating T cells were primed to support the formation of TLSs and facilitate B cell recruitment during HS. Our data definitively demonstrated the presence of TLSs in lesional HS skin and point to ongoing cutaneous B cell maturation through class switch recombination and affinity maturation during disease progression in this inflamed nonlymphoid tissue.

Tertiary Lymphoid Structures Sustain Cutaneous B cell Activity in Hidradenitis Suppurativa

Background

Hidradenitis suppurativa (HS) skin lesions are highly inflammatory and characterized by a large immune infiltrate. While B cells and plasma cells comprise a major component of this immune milieu the biology and contribution of these cells in HS pathogenesis is unclear.

Objective

We aimed to investigate the dynamics and microenvironmental interactions of B cells within cutaneous HS lesions.

Methods

We combined histological analysis, single-cell RNA-sequencing (scRNAseq), and spatial transcriptomic profiling of HS lesions to define the tissue microenvironment relative to B cell activity within this disease.

Results

Our findings identify tertiary lymphoid structures (TLS) within HS lesions and describe organized interactions between T cells, B cells, antigen presenting cells and skin stroma. We find evidence that B cells within HS TLS actively undergo maturation, including participation in germinal center reactions and class switch recombination. Moreover, skin stroma and accumulating T cells are primed to support the formation of TLS and facilitate B cell recruitment during HS.

Conclusion

Our data definitively demonstrate the presence of TLS in lesional HS skin and point to ongoing cutaneous B cell maturation through class switch recombination and affinity maturation during disease progression in this inflamed non-lymphoid tissue.

Xenograft Skin Model to Manipulate Human Immune Responses In Vivo

The human skin xenograft model, in which human donor skin is transplanted onto an immunodeficient mouse host, is an important option for translational research in skin immunology. Murine and human skin differ substantially in anatomy and immune cell composition. Therefore, traditional mouse models have limitations for dermatological research and drug discovery. However, successful xenotransplants are technically challenging and require optimal specimen and mouse graft site preparation for graft and host survival. The present protocol provides an optimized technique for transplanting human skin onto mice and discusses necessary considerations for downstream experimental aims. This report describes the appropriate preparation of a human donor skin sample, assembly of a surgical setup, mouse and surgical site preparation, skin transplantation, and post-surgical monitoring. Adherence to these methods allows for maintenance of xenografts for over 6 weeks post-surgery. The techniques outlined below allow maximum grafting efficiency due to the development of engineering controls, sterile technique, and pre- and post-surgical conditioning. Appropriate performance of the xenograft model results in long-lived human skin graft samples for experimental characterization of human skin and preclinical testing of compounds in vivo.

Transcriptomic Profiling of Plaque Psoriasis and Cutaneous T-Cell Subsets during Treatment with Secukinumab

The IL-17A inhibitor secukinumab is efficacious for the treatment of psoriasis. To better understand its mechanism of action, we investigated its impact on psoriatic lesions from 15 patients with moderate-to-severe plaque psoriasis undergoing secukinumab treatment. We characterized the longitudinal transcriptomic changes of whole lesional skin tissue as well as cutaneous CD4⁺ and CD8⁺ T effector cells and CD4⁺ T regulatory cells across 12 weeks of treatment. Secukinumab was clinically effective and reduced disease-associated overexpression of IL17A , IL17F, IL23A, IL23R, and IFNG in whole tissue as soon as 2 weeks after initiation of treatment. IL17A overexpression in T-cell subsets, primarily CD8⁺ T cells, was also reduced. Although secukinumab treatment resolved 89‒97% of psoriasis-associated expression differences in bulk tissue and T-cell subsets by week 12 of treatment, we observed expression differences involved in IFN signaling and metallothionein synthesis that remained unresolved at this time point as well as potential treatment-associated expression differences involved in IL-15 signaling. These changes were accompanied by shifts in broader immune cell composition on the basis of deconvolution of RNA-sequencing data. In conclusion, our study reveals several phenotypic and cellular changes within the lesion that underlie clinical improvement from secukinumab.

Early-life inflammation primes a T helper 2 cell-fibroblast niche in skin

Inflammation early in life can prime the local immune milieu of peripheral tissues, which can cause lasting changes in immunological tone that confer disease protection or susceptibility¹. The cellular and molecular mechanisms that prompt changes in immune tone in many nonlymphoid tissues remain largely unknown. Here we find that time-limited neonatal inflammation induced by a transient reduction in neonatal regulatory T cells causes a dysregulation of subcutaneous tissue in mouse skin. This is accompanied by the selective accumulation of type 2 helper T (T_H2) cells within a distinct microanatomical niche. T_H2 cells are maintained into adulthood through interactions with a fibroblast population in skin fascia that we refer to as T_H2-interacting fascial fibroblasts (TIFFs), which expand in response to T_H2 cytokines to form subcutaneous fibrous bands. Activation of the T_H2-TIFF niche due to neonatal inflammation primes the skin for altered reparative responses to wounding. Furthermore, we identify fibroblasts in healthy human skin that express the TIFF transcriptional signature and detect these cells at high levels in eosinophilic fasciitis, an orphan disease characterized by inflammation and fibrosis of the skin fascia. Taken together, these data define a previously unidentified T_H2 cell niche in skin and functionally characterize a disease-associated fibroblast population. The results also suggest a mechanism of immunological priming whereby inflammation early in life creates networks between adaptive immune cells and stromal cells to establish an immunological set-point in tissues that is maintained throughout life.

Single-cell RNA sequencing of psoriatic skin identifies pathogenic Tc17 cell subsets and reveals distinctions between CD8+ T cells in autoimmunity and cancer

BACKGROUND

Psoriasis is an inflammatory, IL-17-driven skin disease in which autoantigen-induced CD8⁺ T cells have been identified as pathogenic drivers.

OBJECTIVE

Our study focused on comprehensively characterizing the phenotypic variation of CD8⁺ T cells in psoriatic lesions.

METHODS

We used single-cell RNA sequencing to compare CD8⁺ T-cell transcriptomic heterogeneity between psoriatic and healthy skin.

RESULTS

We identified 11 transcriptionally diverse CD8⁺ T-cell subsets in psoriatic and healthy skin. Among several inflammatory subsets enriched in psoriatic skin, we observed 2 Tc17 cell subsets that were metabolically divergent, were developmentally related, and expressed CXCL13, which we found to be a biomarker of psoriasis severity and which achieved comparable or greater accuracy than IL17A in a support vector machine classifier of psoriasis and healthy transcriptomes. Despite high coinhibitory receptor expression in the Tc17 cell clusters, a comparison of these cells with melanoma-infiltrating CD8⁺ T cells revealed upregulated cytokine, cytolytic, and metabolic transcriptional activity in the psoriatic cells that differed from an exhaustion program.

CONCLUSION

Using high-resolution single-cell profiling in tissue, we have uncovered the diverse landscape of CD8⁺ T cells in psoriatic and healthy skin, including 2 nonexhausted Tc17 cell subsets associated with disease severity.

Developing Human Skin Contains Lymphocytes Demonstrating a Memory Signature

Lymphocytes in barrier tissues play critical roles in host defense and homeostasis. These cells take up residence in tissues during defined developmental windows, when they may demonstrate distinct phenotypes and functions. Here, we utilized mass and flow cytometry to elucidate early features of human skin immunity. Although most conventional αβ T (Tconv) cells in fetal skin have a naive, proliferative phenotype, a subset of CD4⁺ Tconv and CD8⁺ cells demonstrate memory-like features and a propensity for interferon (IFN)γ production. Skin regulatory T cells dynamically accumulate over the second trimester in temporal and regional association with hair follicle development. These fetal skin regulatory T cells (Tregs) demonstrate an effector memory phenotype while differing from their adult counterparts in expression of key effector molecules. Thus, we identify features of prenatal skin lymphocytes that may have key implications for understanding antigen and allergen encounters in utero and in infancy.

CyTOF reveals a complex lymphocyte landscape in developing human skin

Developing skin contains CD45RO⁺ conventional T cells with propensity to produce IFNγ

Regulatory T cells (Tregs) in skin before birth display effector memory properties

Skin Tregs increase in conjunction with initial hair follicle morphogenesis

Immunopathogenesis of hidradenitis suppurativa and response to anti-TNF-α therapy

Hidradenitis suppurativa (HS) is a highly prevalent, morbid inflammatory skin disease with limited treatment options. The major cell types and inflammatory pathways in skin of patients with HS are poorly understood, and which patients will respond to TNF-α blockade is currently unknown. We discovered that clinically and histologically healthy appearing skin (i.e., nonlesional skin) is dysfunctional in patients with HS with a relative loss of immune regulatory pathways. HS skin lesions were characterized by quantitative and qualitative dysfunction of type 2 conventional dendritic cells, relatively reduced regulatory T cells, an influx of memory B cells, and a plasma cell/plasmablast infiltrate predominantly in end-stage fibrotic skin. At the molecular level, there was a relative bias toward the IL-1 pathway and type 1 T cell responses when compared with both healthy skin and psoriatic patient skin. Anti–TNF-α therapy markedly attenuated B cell activation with minimal effect on other inflammatory pathways. Finally, we identified an immune activation signature in skin before anti–TNF-α treatment that correlated with subsequent lack of response to this modality. Our results reveal the fundamental immunopathogenesis of HS and provide a molecular foundation for future studies focused on stratifying patients based on likelihood of clinical response to TNF-α blockade.

Hidradenitis suppurativa lesions are characterized by alterations in cDC2s, relatively reduced Tregs, an influx of memory B cells and plasma cells, and biases towards IL1 pathway activation and type 1 T cell responses.

RNA-seq and flow-cytometry of conventional, scalp, and palmoplantar psoriasis reveal shared and distinct molecular pathways

It has long been recognized that anatomic location is an important feature for defining distinct subtypes of plaque psoriasis. However, little is known about the molecular differences between scalp, palmoplantar, and conventional plaque psoriasis. To investigate the molecular heterogeneity of these psoriasis subtypes, we performed RNA-seq and flow cytometry on skin samples from individuals with scalp, palmoplantar, and conventional plaque psoriasis, along with samples from healthy control patients. We performed differential expression analysis and network analysis using weighted gene coexpression network analysis (WGCNA). Our analysis revealed a core set of 763 differentially expressed genes common to all sub-types of psoriasis. In contrast, we identified 605, 632, and 262 genes uniquely differentially expressed in conventional, scalp, and palmoplantar psoriasis, respectively. WGCNA and pathway analysis revealed biological processes for the core genes as well as subtype-specific genes. Flow cytometry analysis revealed a shared increase in the percentage of CD4+ T regulatory cells in all psoriasis subtypes relative to controls, whereas distinct psoriasis subtypes displayed differences in IL-17A, IFN-gamma, and IL-22 production. This work reveals the molecular heterogeneity of plaque psoriasis and identifies subtype-specific signaling pathways that will aid in the development of therapy that is appropriate for each subtype of plaque psoriasis.

An open-label study of anakinra for the treatment of moderate to severe hidradenitis suppurativa

BACKGROUND

Hidradenitis suppurativa (HS) is a chronic inflammatory disorder characterized by sterile abscesses and fistulae predominantly affecting the axillae and groin. Various biologic agents have been attempted for HS, but there is still no definitive treatment.

OBJECTIVES

We sought to evaluate the efficacy, safety, and tolerability of anakinra in the treatment of moderate to severe HS.

METHODS

Six patients with moderate to severe HS were enrolled in an open-label study with all patients receiving active treatment for 8 weeks with an additional 8 weeks of follow-up off therapy.

RESULTS

The 5 patients who completed the 8-week therapy showed a significant mean decrease in their modified Sartorius score of 34.8 points. The physician and patient global assessment of overall activity showed significant reductions between baseline and 8 weeks of therapy: 45.8 points and 35.6 points, respectively. The Dermatology Life Quality Index showed a significant reduction after 8 weeks of treatment with anakinra. Functional T-cell analysis revealed that patients had increased percentages of CD3(+) T cells in lesional skin compared with nonlesional skin before therapy.

LIMITATIONS

The limited number of patients and lack of control group are limitations.

CONCLUSIONS

Anakinra demonstrated decreased HS disease activity by both objective and subjective measures.

Paradoxical role of PGE2 and cAMP in Actinobacillus actinomycetemcomitants strain Y4-induced lymphocyte proliferation

An immune mechanism has been suggested in the pathogenesis of periodontal disease. Actinobacillus actinomycetemcomitants (Aa) has been implicated as one of the etiological agents that induces the major immune response together with a dense infiltrate of inflammatory cells. But the exact role of these immune cells in periodontal disease has not yet been clarified. In this study the T lymphocyte (TL) proliferative response was evaluated after having being exposed to free cell supernatant (SN) from Aa. Aa SN increased TL proliferation. This mitogenic effect of Aa SN was attenuated by pretreating TL with indomethacin (INDO) or acetylsalicylic acid (ASA) but not by polymyxin B. The inhibitory effect of INDO on cell proliferation was reversed by the addition of prostaglandin E2 (PGE2) to the culture assay. Moreover, when immune cells were exposed to Aa SN they were able to generate PGE2 at the same time as intracellular levels of cAMP decreased. Both, PGE2 release and decrease accumulation of cAMP in TL were blunted by treated lymphocytes with INDO. In this paper we demonstrate that cell free SN from Aa induces a mitogenic effect on murine lymphocytes. The mechanism involves the host's immunecompetent cells and the release of PGE2 and appears not to be induced by capsular-like polysaccharide antigen. Results show a paradoxical mitogenic effect of Aa SN accompanied by increased generation of PGE2 and decreased production of cAMP by lymphocytes.

Contemporary classification of histiocytic disorders. The WHO Committee On Histiocytic/Reticulum Cell Proliferations. Reclassification Working Group of the Histiocyte Society

Pathologists and pediatric hematologist/ oncologists of the World Health Organization's Committee on Histiocytic/Reticulum Cell Proliferations and the Reclassification Working Group of the Histiocyte Society present a classification of the histiocytic disorders that primarily affect children. Nosology, based on the lineage of lesional cells and biological behavior, is related to the ontogeny of histiocytes (macrophages and dendritic cells of the immune system). Dendritic cell-related disorders of varied biological behavior are dominated by Langerhans cell histiocytosis, but separate secondary proliferations of dendritic cells must be differentiated. Juvenile xanthogranuloma represents a disorder of dermal dendrocytes, another dendritic cell of skin. The hemophagocytic syndromes are the most common of the macrophage-related disorders of varied biological behavior. Guidelines for distinguishing the exceedingly rare malignant diseases of histiocytes from large cell lymphomas through the use of a battery of special studies are provided.

Pseudohypertriglyceridaemia

A mistake can be made in interpreting plasma triglyceride levels since in some cases pseudohypertriglyceridaemia may result from increased plasma glycerol due to a glycerol kinase deficit. Most automated triglyceride assays used in laboratories do not contain a negative control, i.e. a glycerol assay. We report two cases with pseudohypertriglyceridaemia due to hyperglycerolaemia and describe the clinical and biological features which suggested the diagnosis.

Contemporary classification of histiocytic disorders. The WHO Committee On Histiocytic/Reticulum Cell Proliferations. Reclassification Working Group of the Histiocyte Society

Pathologists and pediatric hematologist/ oncologists of the World Health Organization's Committee on Histiocytic/Reticulum Cell Proliferations and the Reclassification Working Group of the Histiocyte Society present a classification of the histiocytic disorders that primarily affect children. Nosology, based on the lineage of lesional cells and biological behavior, is related to the ontogeny of histiocytes (macrophages and dendritic cells of the immune system). Dendritic cell-related disorders of varied biological behavior are dominated by Langerhans cell histiocytosis, but separate secondary proliferations of dendritic cells must be differentiated. Juvenile xanthogranuloma represents a disorder of dermal dendrocytes, another dendritic cell of skin. The hemophagocytic syndromes are the most common of the macrophage-related disorders of varied biological behavior. Guidelines for distinguishing the exceedingly rare malignant diseases of histiocytes from large cell lymphomas through the use of a battery of special studies are provided.

[Tap water iontophoresis in the treatment of hyperhidrosis of the hands and feet]

Seven patients with hyperhidrosis of the palms or soles resistant to topical application of aluminum chloride solution were treated successfully with tap water iontophoresis. After an average of 10 or 11 treatments 80% sweating suppression was found on palms and 74% suppression on soles. As side effects of treatment discomfort and transient skin irritation were observed depending on the amperage used. The effect lasts up to several weeks; however, maintenance treatment on an individual schedule is required.