Lesional Hidradenitis Suppurativa Skin Research Articles

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.

Tape strips detect molecular alterations and cutaneous biomarkers in skin of patients with hidradenitis suppurativa

Hidradenitis suppurativa (HS) has a high unmet need for better treatments. Biopsies are considered the gold standard for studying molecular alterations in skin. A reproducible, minimally invasive approach is needed for longitudinal monitoring in trials and in pediatric populations. To determine whether skin tape strips can detect molecular alterations in HS and identify biomarkers of disease activity. We performed RNA sequencing on tape strips collected from lesional and healthy-appearing (nonlesional) HS skin (n=22) and healthy controls (n=21). We correlated the expression of skin biomarkers between tape strips and a previously published gene-signature of HS biopsies. Tape strips detected upregulation of known HS biomarkers (eg, Interleukin[IL]-17A) in nonlesional and/or lesional skin and also identified novel clinically actionable targets, including OX40 and JAK3. The expression of Th17 and tumor necrosis factor-α pathways were highly correlated between tape strips and biopsies. HS clinical severity was significantly associated with expression of biomarkers (eg tumor necrosis factor-α , IL-17A/F, OX40, JAK1-3, IL-4R) in HS lesional and/or nonlesional skin. Sample size. Tape stripping is limited in depth. This study validates tape strips as a minimally-invasive approach to identify cutaneous biomarkers in HS. This provides a novel avenue for monitoring treatment efficacy and a potential step toward individualized therapy in HS.

Innate lymphoid cell (ILC) subsets are enriched in the skin of patients with hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a chronic relapsing inflammatory skin disease manifested as painful inflamed lesions including deep-seated nodules, abscesses and sinus tracts. The exact aetiology of HS is unclear. Recent evidence suggests that immune dysregulation plays a crucial role in pathogenesis and disease progression. Innate lymphoid cells (ILC) are a recently identified immune cell subset involved in mediating immunity, however their role in HS has not yet been investigated. Three distinct subsets of ILC- ILC1, ILC2 and ILC3 have been described, and these are involved in skin tissue homeostasis and pathologic inflammation associated with autoimmunity and allergic diseases. In this study, we analysed by multiparameter flow cytometry the frequencies of ILC subsets in skin and peripheral blood mononuclear cells (PBMC) of HS patients and compared these to healthy control subjects and psoriasis patients. The absolute numbers of total ILC and subsets thereof were significantly reduced in the blood of HS patients relative to healthy controls. However, when patients were stratified according to treatment, this reduction was no longer observed in patients undergoing anti-TNF treatment. In HS lesional skin the absolute numbers of ILC were significantly increased relative to control skin. Furthermore, the frequencies of total ILC as well as ILC2 and ILC3 were significantly higher in non-lesional than lesional HS skin. This study analysed for the first time the presence of ILC subsets in the blood and skin of HS patients. Our findings suggest that ILC may participate in HS pathogenesis.

New Data on the Features of Skin Barrier in Hidradenitis Suppurativa.

Hidradenitis suppurativa (HS) is a Th1/17-driven inflammatory skin disease of the apocrine gland-rich (AGR) skin regions, where keratinocytes seem to be the crucial drivers of the initial pathogenic steps. However, the possible role of permeability barrier alteration in activating keratinocytes during HS development has not been clarified. We compared the major permeability barrier elements of non-lesional HS (HS-NL; n = 10) and lesional HS (HS-L; n = 10) skin with healthy AGR regions (n = 10) via RT-qPCR and immunohistochemistry. Stratum corneum components related to cornified envelope formation, corneocyte desquamation and (corneo)desmosome organization were analyzed along with tight junction molecules and barrier alarmins. The permeability barrier function was also investigated with transepidermal water loss (TEWL) measurements (n = 16). Junction structures were also visualized using confocal microscopy. At the gene level, none of the investigated molecules were significantly altered in HS-NL skin, while 11 molecules changed significantly in HS-L skin versus control. At the protein level, the investigated molecules were similarly expressed in HS-NL and AGR skin. In HS-L skin, only slight changes were detected; however, differences did not show a unidirectional alteration, as KRT1 and KLK5 were detected in decreased levels, and KLK7, KRT6 and DSG1 in increased levels. No significant differences in TEWL or the expression of junction structures were assessed. Our findings suggest that the permeability barrier is not significantly damaged in HS skin and permeability barrier alterations are not the driver factors of keratinocyte activation in this disease.

355 Permeability barrier characteristics of hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic, inflammatory skin disease of the apocrine gland-rich (AGR) skin regions with a well characterized Th1/17 cytokine milieu. According to current literature data, keratinocytes are crucial drivers of the first pathogenic steps of HS. However, the possible role of permeability barrier alteration, as KC activating event, has not been studied in detailed in HS. Our main focus was to study the permeability barrier of non-lesional HS (HS NL) and lesional HS (HS L) skin and compare them to that of the healthy AGR region.

B-cell and complement signature in severe hidradenitis suppurativa that does not respond to adalimumab.

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disorder with significant morbidity. The pathogenesis remains incompletely understood although immune dysregulation plays an important role. It is challenging to treat and approximately 50% of patients respond clinically to adalimumab, the only licensed treatment. To examine differences between lesional and nonlesional HS skin at baseline using bulk RNA sequencing, and to compare the transcriptome in the skin before and after 12 weeks of treatment with adalimumab. To examine transcriptomic differences between adalimumab responders and nonresponders using Hidradenitis Suppurativa Clinical Response and the International Hidradenitis Suppurativa Severity Score System (IHS4); and to compare transcriptomic differences based on disease severity (Hurley stage and IHS4). We completed bulk RNA sequencing on lesional and nonlesional skin samples of patients before and after 12 weeks of treatment with adalimumab. Baseline differentially expressed genes and pathways between lesional and nonlesional skin highlighted chemokines and antimicrobial peptides produced by keratinocytes; B-cell function; T-cell-receptor, interleukin-17 and nuclear factor-κB signalling; and T-helper-cell differentiation. Transcriptomic differences were identified in lesional skin at baseline, between subsequent responders and nonresponders. Patients with severe HS who did not respond to adalimumab had enriched complement and B-cell activation pathways at baseline. In addition, logistic regression identified CCL28 in baseline lesional HS skin as a potential biomarker of treatment response. This highlights the potential for targeting B-cell and complement pathways in HS treatment and the potential of stratifying patients at baseline to the most suitable treatment based on the skin transcriptome. CCL28 has not previously been identified in HS skin and has potential clinical relevance due to its antimicrobial function and homing of B and T cells at epithelial surfaces. Our results provide data to inform future translational and clinical studies on therapeutics in HS.

Antimicrobial peptides in hidradenitis suppurativa: a systematic review.

Hidradenitis suppurativa (HS) is a chronic, inflammatory skin disease of the hair follicle defined by recurrent nodules, tunnels and scarring involving the intertriginous regions. HS is associated with microbial dysbiosis and immune dysregulation. In HS, an increasing number of studies have investigated antimicrobial peptides (AMPs). To provide an overview of the literature on AMPs in HS, and to discuss the potential role of AMPs in the pathogenesis of HS. PubMed, Embase and the Cochrane Library were searched. The titles, abstracts and full texts of all articles were manually screened. Additionally, the reference lists of the included articles were screened and hand searched for relevant studies. The final literature sample comprised 18 retrospective and prospective studies (no reviews or commentaries) published between 2009 and 2020. This review demonstrates the multitude of AMPs in HS. Although the methodology of the studies varied, the included studies indicate a consistent overexpression of human β-defensin (hBD)-2, S100A7, S100A8 and S100A9 at both the mRNA and protein levels, and a decreased expression of hBD-1. Overall, the studies point to a dysregulation of AMPs in both lesional and nonlesional HS skin.

227 Primary Changes in the Development of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic, inflammatory skin disease of the apocrine gland-rich (AGR) skin region. Although the immune alteration in lesional HS skin is well-characterized the initial steps of the disease are not fully understood. We aimed to investigate the immune characteristics of non-lesional HS skin, representing the first stage of HS development, and to compare that with lesional HS skin as well as healthy AGR region. Our main focus was to study the immune components showing significantly different levels between AGR and lesional HS skin samples in our previously published report. Immune cell counts (T cells, dendritic cells, macrophages), T helper (Th)1/Th17-related molecules (IL-12B, TBX21, IFNG, TNFA, IL-17, IL-10, IL-23A, TGFB1, RORC, CCL20), keratinocyte (KC)-related sensors, mediators (S100A7, S100A8, S100A9, DEFB4B, LCN2, CAMP), proinflammatory molecules (TLR2, TLR4, IL-1B, IL6, TNFA, IL-23A) and chemokines (CCL2) were investigated in the three sample groups by multiple mRNA (RNAseq and RT-qPCR) and protein-based (IHC and IF) methods. According to our findings, when comparing non-lesional HS and AGR skin, KC-derived antimicrobial peptides were highly upregulated in the non-lesional HS skin. The epidermal occurrence of IL-1β, TNF-α and IL-23 were also significantly increased in the non-lesional HS epidermis but not in the dermis. On the contrary, no significant differences were detected regarding the dermal cellular components and Th1/Th17-related mediators. In summary, our results indicate KCs as crucial players in the first stages of HS development since all the investigated KC-derived molecules’ expression were increased even in non-lesional HS skin in contrast to the (adaptive) dermal components which showed similar levels in AGR and non-lesional HS skin but were prominently elevated in lesional HS skin in parallel with to the further enhancement of the innate immune components.

049 Janus Kinase 1 Inhibitor INCB054707 Modulates Disease-Associated Markers and Pathways in Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition with recurrent painful nodules, abscesses, and sinus tract formation leading to irreversible tissue damage and scarring. Previous transcriptome analyses have identified markers that are significantly elevated in lesional HS skin, including cytokines (interleukin [IL]-1α, IL-6, tumor necrosis factor [TNF]-α, IL-17, IL-12/23, IL-10), interferon family members, Toll-like receptor 2, antimicrobial peptides, and tyrosine kinases (Janus kinase [JAK] 1/3, BTK, SYK) and their downstream signaling partners.

The inflammatory proteome of hidradenitis suppurativa skin is more expansive than that of psoriasis vulgaris

Although hidradenitis suppurativa (HS) shares some transcriptomic and cellular infiltrate features with psoriasis, their skin proteome remains unknown. To define and compare inflammatory protein biomarkers of HS and psoriasis skin. We assessed 92 inflammatory biomarkers in HS (n=13), psoriasis (n=11), and control skin (n=11) using Olink high-throughput proteomics. We also correlated HS skin and blood biomarkers using proteomics and RNA sequencing. We identified 57 differentially expressed proteins (DEPs) in lesional psoriasis and 64 DEPs in lesional HS skin, compared to healthy controls. Both HS and psoriasis lesional skin demonstrated a significant upregulation of T helper 1 and T helper 17 proteins. Healthy-appearing perilesional HS skin had 63 DEPs compared to healthy controls. Nonlesional HS and psoriasis skin had 24 and 7 DEPs, respectively, compared to healthy controls. Tumor necrosis factor and 8 other proteins were significantly correlated with clinical severity in perilesional HS skin (2cm from a nodule). Inclusion of only moderate-to-severe patients and the cohort size. HS has a greater inflammatory profile and is more diffusely distributed compared with psoriasis. Proteins correlated with disease severity are potential disease mediators. Perilesional skin is comparably inflamed to lesional skin, suggesting the need to treat beyond skin nodules.

14928 Epithelialized tracts are active mediators of inflammation in hidradenitis suppurativa

Introduction: Hidradenitis suppurativa (HS) is a chronic, inflammatory disease characterized by painful nodules, abscesses and draining sinuses, most commonly occurring in the inguinal, axillary, and submammary areas. Severe disease is associated with discharging sinus tracts and fibrotic scarring. The development of dermal tunnels and interconnecting tracts is poorly understood, and has traditionally been considered an end-stage feature of disease. Methods/Results: After receiving approval from the Rockefeller University’s Institutional Review Board, unaffected, perilesional and lesional HS skin was collected by punch biopsies.

Serum Concentration and Skin Expression of S100A7 (Psoriasin) in Patients Suffering from Hidradenitis Suppurativa

Background: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease. An important role of innate immune dysregulation in the pathogenesis of HS has been highlighted. S100A7 (psoriasin) is an innate, antimicrobial protein that exerts proinflammatory and chemotactic action. Objectives: The objective of the study was to investigate serum concentrations of S100A7 in individuals with HS as compared to healthy controls. Further, we evaluated the expression of S100A7 in lesional HS skin as compared to perilesional (clinically uninvolved) HS skin and normal skin. Methods: Serum concentrations of S100A7 were evaluated with a commercially available ELISA kit. The expression of S100A7 in the skin was assessed using qRT-PCR and immunofluorescence staining. Results: We found increased expression of S100A7 in lesional HS skin as compared to perilesional HS skin (p = 0.0017). The expression of S100A7 in lesional HS skin was positively associated with serum C-reactive protein concentration and the severity of disease according to Hurley staging. The serum concentration of S100A7 in individuals with HS was decreased as compared to healthy controls and patients with psoriasis. Conclusions: Upregulated in lesional HS skin, S100A7 may enhance the inflammatory process and contribute to the HS pathogenesis.

Increased expression profile of NCSTN, Notch and PI3K/AKT3 in hidradenitis suppurativa.

In a small number of kindreds with familial hidradenitis suppurativa (HS) different mutations of NCSTN (nicastrin) have been identified. Blocking of NCSTN leads to impairment of the Notch and PI3K/AKT signalling pathway, which is assumed to play a pathogenic role in HS. However, very limited data are available concerning expression levels of these pathway components in HS skin. To analyse the mRNA and protein expression of NCSTN, Notch1-3, PIK3R3 and AKT3 in HS. Skin samples from healthy controls, lesional and perilesional skin of HS patients with and without a positive family history were analysed by quantitative real-time RT-PCR and immunohistochemistry. Univariate statistical analyses were conducted regarding association between expression levels and patient's characteristics. Expression levels of all investigated genes showed significantly higher levels in lesional HS skin compared with healthy controls. Univariate analysis showed no association between a positive family history and mRNA expression levels. Perilesional HS skin of patients with mild disease severity (Hurley I) showed significant higher mRNA expression levels of the investigated pathway components compared to moderate (Hurley II) and severe disease (Hurley III). We found no evidence for diminished expression levels of the Notch signalling. In contrast, the NCSTN, Notch and PI3K/AKT signalling components are overexpressed in HS. Future research is needed to investigate a possible pathogenetic role or to reveal a coactivation of these overexpressed components during inflammatory response in HS.

Transcriptomic analysis of hidradenitis suppurativa skin suggests roles for multiple inflammatory pathways in disease pathogenesis.

Hidradenitis suppurativa (HS) is a chronic inflammatory disease with limited treatment options; therefore, the current study investigated the downstream signaling pathways that are differentially expressed in HS subjects and may drive disease pathogenesis. The expression of 144 genes was evaluated in the skin of 16 healthy subjects and 34 subjects with mild to severe HS using QuantiGene Plex assay. One hundred and twenty-nine genes were significantly elevated in lesional HS skin as compared to the skin of healthy controls including pro-inflammatory cytokines (IL-1α, IL-6, TNF-α), IL-17-associated cytokines (IL-17A, IL-17F, IL-23A), the IL-10 family of cytokines (IL-10, IL-19, IL-20, IL-22, IL-24), and IFN family members (IFNA1, IFNB1, IFNG, IL-12B). This corresponded with increased expression of tyrosine kinases (JAK1, JAK3, BTK, SYK) and their downstream signaling partners (STAT1, STAT2, STAT3, STAT5A, STAT5B, STAT6). These data illustrate the diverse immune activation in lesional HS skin and suggest that deeper interrogation of the disease heterogeneity may reveal unique opportunities for targeted therapies in designated subpopulations.

062 Hidradenitis suppurativa RNA-seq skin transcriptome overlaps with psoriasis vulgaris and reveals a marked upregulation of multiple targetable cytokines

Hidradenitis Suppurativa (HS) is a chronic inflammatory dermatosis of inguinal, axillary, and submammary skin. Using established consensus definitions, unaffected, perilesional and lesional HS skin samples were collected and RNA-sequencing performed. A mixed-effect model was estimated. Hypotheses were tested under the general framework for linear models in the R limma package. P values from t-tests were adjusted for multiple hypotheses using the Benjamini–Hochberg procedure. Statistical analysis revealed a HS transcriptome of approximately 5000 genes (FCH>1.5; fdr<0.05), with HS samples clustering distinctly away from control skin.

Lipidomics Profiling of Hidradenitis Suppurativa Skin Lesions Reveals Lipoxygenase Pathway Dysregulation and Accumulation of Proinflammatory Leukotriene B4

Hidradenitis suppurativa (HS) is a chronic, recurring inflammatory dermatosis characterized by abscesses, deep-seated nodules, sinus tracts, and fibrosis in skin lesions around hair follicles of the axillary, inguinal, and anogenital regions. Whereas the exact pathogenesis remains poorly defined, clear evidence suggests that HS is a multifactorial inflammatory disease characterized by innate and adaptive immune components. Bioactive lipids are important regulators of cutaneous homeostasis, inflammation, and resolution of inflammation. Alterations in the lipid mediator profile can lead to malfunction and cutaneous inflammation. We used targeted lipidomics to analyze selected omega-3 and omega-6 polyunsaturated fatty acids in skin of patients with HS and of healthy volunteers. Lesional HS skin displayed enrichment of 5-lipoxygenase (LO)‒derived metabolites, especially leukotriene B4. In addition, 15-LO‒derived metabolites were underrepresented in HS lesions. Changes in the lipid mediator profile were accompanied by transcriptomic dysregulation of the 5-LO and 15-LO pathways. Hyperactivation of the 5-LO pathway in lesional macrophages identified these cells as potential sources of leukotriene B4, which may cause neutrophil influx and activation. Furthermore, leukotriene B4-induced mediators and pathways were elevated in HS lesions, suggesting a contribution of this proinflammatory lipid meditator to the pathophysiology of HS.

Lesional Inflammatory Profile in Hidradenitis Suppurativa Is Not Solely Driven by IL-1

Lesional Inflammatory Profile in Hidradenitis Suppurativa Is Not Solely Driven by IL-1

The skin transcriptome in hidradenitis suppurativa uncovers an antimicrobial and sweat gland gene signature which has distinct overlap with wounded skin.

Hidradenitis suppurativa (HS) is a debilitating chronic inflammatory skin disease resulting in non-healing wounds affecting body areas of high hair follicle and sweat gland density. The pathogenesis of HS is not well understood but appears to involve dysbiosis-driven aberrant activation of the innate immune system leading to excessive inflammation. Marked dysregulation of antimicrobial peptides and proteins (AMPs) in HS is observed, which may contribute to this sustained inflammation. Here, we analyzed HS skin transcriptomes from previously published studies and integrated these findings through a comparative analysis with a published wound healing data set and with immunofluorescence and qPCR analysis from new HS patient samples. Among the top differently expressed genes between lesional and non-lesional HS skin were members of the S100 family as well as dermcidin, the latter known as a sweat gland-associated AMP and one of the most downregulated genes in HS lesions. Interestingly, many genes associated with sweat gland function, such as secretoglobins and aquaporin 5, were decreased in HS lesional skin and we discovered that these genes demonstrated opposite expression profiles in healing skin. Conversely, HS lesional and wounded skin shared a common gene signature including genes encoding for S100 proteins, defensins, and genes encoding antiviral proteins. Overall, our results suggest that the pathogenesis of HS may be driven by changes in AMP expression and altered sweat gland function, and may share a similar pathology with chronic wounds.

MON-218 Inflammatory Role of Sex Steroids in Hidradenitis Suppurativa: An Androgenic Phenotype

Hidradenitis Suppurativa (HS) is an autoinflammatory skin disease more common in women and associated with hyper-androgenic disorders such as polycystic ovary syndrome. HS is characterized by chronic recurrent deep-seated painful nodules and draining tunnels in skin areas that follow the distribution of pubertal terminal hair growth. In women, HS disease activity varies with hormonal fluctuation across the menstrual cycle and pregnancy. Anti-androgens have shown promise in treatment of HS, but the pathophysiologic link between sex hormones and HS is unclear. We sought to further elucidate the role of sex hormones in the pathogenesis of HS. Objective: To determine if there is differential estrogen and androgen regulated gene expression in lesional compared to non-lesional skin transcriptome in HS patients. Methods: (a) We analyzed mRNA microarray data from lesional and non-lesional HS skin (GEO, GSE72702) (Blok JL, Br J Dermatol. 2016;174(6):1392). Inflammatory lesional skin from affected axilla or groin and non-lesional skin from the upper arm or leg was obtained from 17 patients with moderate to severe HS. We then examined differential expression of hormone regulated genes identified in existing androgen and estrogen gene expression signatures from prostate cancer cells [(VCaP treated with dihydrotestosterone (DHT)] and breast cancer cells [MCF7 treated with 17 beta-estradiol, (E2)] in the lesional and non-lesional skin transcriptomes of the HS patients. We identified overlap between the sets of genes that were either both upregulated or both repressed in HS lesions and the hormone-responsive prostate and breast cancer cell line models. Significance of differential gene expression was defined as FDR-adjusted p-value for two-tailed Student t-test less than 0.05. (b) After overlapping genes were identified, we used GeneGo Metacore pathway analysis software to explore the functional significance of the identified genes. Results: (a) Of the 3379 E2-upregulated probe sets in MCF7 breast cancer cells, 647 were significantly upregulated and 584 of 2871 E2-downregulated probe sets were significantly downregulated in HS lesions. Of the 1328 DHT-upregulated probe sets in prostate cancer cells, 341 were significantly upregulated and 196 of the 1251 DHT-downregulated probe sets were significantly downregulated in HS lesions. (b) Initial pathway analysis indicates that DHT upregulated genes in HS lesions are strongly enriched in innate immunity pathways, specifically, type 1 interferon signaling and class I MHC antigen presentation. Conclusion: There is substantial overlap between the transcriptional programme of sex steroids and transcriptional changes observed in HS lesional skin. In particular, androgen target genes are significantly enriched in innate immunity pathways, suggesting a functional link between the androgen signaling and the inflammatory process in HS lesions.

Reduced ten-eleven translocation and isocitrate dehydrogenase expression in inflammatory hidradenitis suppurativa lesions.

As environmental factors appear to predispose patients to hidradenitis suppurativa (HS), studying epigenetic modifications is of interest to further understand the pathogenesis of HS. To study the expression of DNA hydroxymethylation regulators, namely the ten-eleven translocation (TET) and isocitrate dehydrogenase (IDH) family, in the skin of HS patients. Twenty patients with HS and 12 healthy subjects were recruited. We analysed the expression of TET1, TET2, TET3, IDH1, IDH2, IDH3a, and IDH3b in lesional and perilesional HS tissue as well as tissue from healthy controls by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR). In addition, immunohistochemistry was performed for TET1, TET2, and TET3. RT-PCR analysis showed that mRNA of all the studied genes was significantly under-expressed in lesional HS skin compared to healthy skin. IDH1 and IDH2 mRNA expression was also significantly lower in perilesional HS skin compared to healthy skin, and TET3 mRNA expression was significantly lower in lesional HS skin compared to perilesional HS skin. RT-PCR analysis for TET1, TET2, and TET3 mRNA expression was confirmed by immunohistochemical analysis. Correlation analysis revealed a significant positive correlation between TET and IDH gene expression in perilesional and lesional HS skin. Our results suggest that epigenetic changes occur in HS tissue and that aberrant expression of the DNA hydroxymethylation regulators may play a role in the pathogenesis of HS. As epigenetic modifications are reversible, further research into the cause of these aberrant expression patterns is warranted in order to develop possible novel therapeutic approaches.