Eosinophils Contribute to Oral Tolerance via Induction of RORγt-Positive Antigen-Presenting Cells and RORγt-Positive Regulatory T Cells.

Oral tolerance has been defined as the specific suppression of immune responses to an antigen by prior oral administration of the antigen. It has been thought to serve to suppress food allergy. Previous studies have shown that dendritic cells (DCs) and regulatory T cells (Tregs) are involved in the induction of oral tolerance. However, the detailed mechanisms of Treg induction in oral tolerance remain largely unknown. Eosinophils have been recognized as effector cells in allergic diseases, but in recent years, the diverse functions of tissue-resident eosinophils have been reported. Eosinophils in the intestine have been reported to induce Tregs by releasing TGF-ß, but the role of eosinophils in oral tolerance is still controversial. In this study, we analyzed the roles of eosinophils in oral tolerance using eosinophil-deficient ΔdblGATA mice (mice lacking a high-affinity GATA-binding site in the GATA1 promoter). ΔdblGATA mice showed impaired antigen-induced oral tolerance compared to wild-type mice. The induction of RORγt+ Tregs in mesenteric lymph nodes (MLNs) by oral tolerance induction was impaired in ΔdblGATA mice compared to wild-type mice. An increase in RORγt+ antigen-presenting cells (APCs), which are involved in RORγt+ Treg differentiation, in the intestine and MLNs was not seen in ΔdblGATA mice. Notably, the expansion of group 3 innate lymphoid cells (ILC3s), a subset of RORγt+ APCs, by oral tolerance induction was seen in wild-type mice but not ΔdblGATA mice. These results suggest that eosinophils are crucial in the induction of oral tolerance, possibly via the induction of RORγt+ APCs and RORγt+ Tregs.

Epithelial cell-derived cytokine TSLP activates regulatory T cells by enhancing fatty acid uptake.

Epithelial cells control a variety of immune cells by secreting cytokines to maintain tissue homeostasis on mucosal surfaces. Regulatory T (Treg) cells are essential for immune homeostasis and for preventing tissue inflammation; however, the precise molecular mechanisms by which epithelial cell-derived cytokines function on Treg cells in the epithelial tissues are not well understood. Here, we show that peripheral Treg cells preferentially respond to thymic stromal lymphoprotein (TSLP). Although TSLP does not affect thymic Treg differentiation, TSLP receptor-deficient induced Treg cells derived from naïve CD4+ T cells are less activated in an adoptive transfer model of colitis. Mechanistically, TSLP activates induced Treg cells partially through mTORC1 activation and fatty acid uptake. Thus, TSLP modulates the activation status of induced Treg through the enhanced uptake of fatty acids to maintain homeostasis in the large intestine.

A20 (Tnfaip3) expressed in CD4+ T cells suppresses Th2 cell-mediated allergic airway inflammation in mice.

A20 (Tnfaip3), a ubiquitin-editing enzyme, inhibits NF-κB signaling pathways in response to pro-inflammatory cytokines. Previous studies have proved the anti-inflammatory roles of A20 in various cell types, including T cells, B cells, dendritic cells, and intestinal epithelial cells. Moreover, recent studies have shown that A20 expressed in lung epithelial cells is required for LPS-induced protection from asthma. In humans, a single-nucleotide polymorphism in TNFAIP3 is associated with asthma risk. However, the role of A20 expressed in T cells in asthmatic responses has not been elucidated. We addressed this point by generating mice lacking A20 expression in T cells (CD4-CreA20 fl/fl mice). We found that house dust mite (HDM)-induced allergic airway inflammation, mucus production, airway hyperresponsiveness, and Th2 cytokine production were significantly exacerbated in CD4-CreA20 fl/fl mice compared with those in control A20 fl/fl mice. In vitro differentiation of Th2 cells but not of Th1 cells or Th17 cells was enhanced in CD4+ T cells by the absence of A20. Consistently, enforced expression of A20 inhibited the differentiation of Th2 cells but not of Th1 cells or Th17 cells. Notably, the expression of GATA3 was significantly enhanced in A20-deficient CD4+ T cells, and the enhanced GATA3 expression was partly canceled by IL-2 neutralization. These results suggest that A20 functions as a stabilizing factor maintaining GATA3 levels during the induction of Th2 cells to prevent excessive Th2 cell differentiation.

Airway epithelial STAT3 inhibits allergic inflammation via upregulation of stearoyl-CoA desaturase 1.

BACKGROUND: Airway epithelial cells (AECs) play a crucial role in the induction and development of allergic inflammation through the development and activation of immune cells, including Th2 cells and ILC2s. Recent studies have revealed that STAT3 expressed in epithelial cells protects against pathogens and maintains homeostasis in the intestine. However, the roles of STAT3 in airway epithelium are poorly understood. Therefore, we sought to elucidate the roles of airway epithelial STAT3 in allergic airway inflammation. METHODS: Allergic airway inflammation was induced by intratracheal administration of house dust mite (HDM) extract in doxycycline-induced AEC-specific STAT3-deficient (STAT3-cKO) mice and their genetic control (STAT3-WT) mice. Airway inflammation was evaluated by flow cytometric analysis of bronchoalveolar lavage fluid cells and histological analysis of the lung. Purified airway epithelial cells were analyzed by quantitative PCR and RNA-sequencing (RNA-seq). RESULTS: HDM-induced airway inflammation was exacerbated in STAT3-cKO mice compared with STAT3-WT mice. RNA-seq analyses revealed that Scd1, coding stearoyl-CoA desaturase 1, was most significantly upregulated in HDM-treated STAT3-WT mice compared to HDM-treated STAT3-cKO mice. Notably, the administration of an SCD1 inhibitor exacerbated HDM-induced airway inflammation. AECs of HDM-treated STAT3-cKO mice and those of HDM-treated SCD1 inhibitor-injected mice shared 45 differentially expressed genes (DEGs). Gene enrichment analysis of the DEGs revealed that the enriched ontology clusters included fatty acid biosynthetic process and regulation of lipid biosynthetic process, suggesting the involvement of the STAT3-SCD1-lipid metabolism axis in suppressing allergic inflammation. CONCLUSIONS: STAT3 is crucial for suppressing HDM-induced allergic airway inflammation, possibly inducing SCD1 expression in AECs.

NF-κB1 Contributes to Imiquimod-Induced Psoriasis-Like Skin Inflammation by Inducing Vγ4+Vδ4+γδT17 Cells.

Recent studies have identified NF-κB1 as a new disease susceptibility gene for psoriasis. Although accumulating evidence has shown the importance of NF-κB signaling in various cell types in the pathogenesis of psoriasis, it remains unclear how NF-κB1 contributes to the pathogenesis of psoriasis. In this study, we examined psoriasis-like skin diseases induced by topical administration of imiquimod in Nf-κb1‒deficient (Nf-κb1-/-) mice and littermate wild-type (WT) mice. Compared with WT mice, Nf-κb1-/- mice exhibited attenuated skin inflammation. The numbers of Vγ4+Vδ4+γδT17 cells, which cause skin inflammation in this model, were significantly reduced in the skin and draining lymph nodes in imiquimod-treated Nf-κb1-/- mice. Nf-κb1 is preferentially phosphorylated in Vγ4+Vδ4+γδT17 cells in WT mice. In vitro proliferation of Vγ4+Vδ4+γδT17 cells but not conventional CD4+ T cells was significantly impaired in Nf-κb1-/- mice compared with that in WT mice. RNA-sequencing analyses revealed that the expression of E2 factor target genes was decreased in Vγ4+Vδ4+γδT cells by the absence of NF-κB1. Consistently, the cell cycle progression of Vγ4+Vδ4+γδT cells was reduced in Nf-κb1-/- mice compared with that in WT mice. These results suggest that Nf-κb1 plays a crucial role in the pathogenesis of imiquimod-induced psoriasis-like skin inflammation by promoting the proliferation of Vγ4+Vδ4+γδT17 cells.

Staphylococcus aureus impairs dermal fibroblast functions with deleterious effects on wound healing.

Chronic wounds are a major disease burden worldwide. The breach of the epithelial barrier facilitates transition of skin commensals to invasive facultative pathogens. Therefore, we investigated the potential effects of Staphylococcus aureus (SA) on dermal fibroblasts as key cells for tissue repair. In co-culture systems combining live or heat-killed SA with dermal fibroblasts derived from the BJ-5ta cell line, healthy individuals, and patients with systemic sclerosis, we assessed tissue repair including pro-inflammatory cytokines, matrix metalloproteases (MMPs), myofibroblast functions, and host defense responses. Only live SA induced the upregulation of IL-1ß/-6/-8 and MMP1/3 as co-factors of tissue degradation. Additionally, the increased cell death reduced collagen production, proliferation, migration, and contractility, prerequisite mechanisms for wound closure. Intracellular SA triggered inflammatory and type I IFN responses via intracellular dsDNA sensor molecules and MyD88 and STING signaling pathways. In conclusion, live SA affected various key tissue repair functions of dermal fibroblasts from different sources to a similar extent. Thus, SA infection of dermal fibroblasts should be taken into account for future wound management strategies.

Long-term use of biologic agents does not increase the risk of serious infections in elderly patients with rheumatoid arthritis.

This study aimed to determine whether the long-term use of biologic agents increases serious infections in elderly patients with rheumatoid arthritis (RA) and to determine the risk factors of serious infections in biologics-treated elderly RA patients. We retrospectively analyzed the incidence rate of serious infections that required hospitalization between biologics-treated and non-biologic disease-modifying antirheumatic drug (DMARD)-treated elderly RA patients (aged over 65 years). We examined the risk factors for serious infections in biologics-treated elderly RA patients. We found that, during a 3-year observation period, the incidence rate of serious infections was not significantly different between biologics-treated and non-biologic DMARD-treated elderly RA patients [8.0 (95% CI 4.7-13.5) and 6.3 (95% CI 4.1-9.5) events per 100 person-years of follow-up, respectively, P = 0.78]. The time to the first serious infection did not significantly differ between the two groups by the analysis of the Kaplan-Meier curves, either (P = 0.46). We then found that prednisolone doses alone were significantly associated with serious infections in biologics-treated elderly RA patients. Furthermore, we found that prednisolone at 1-4 mg/day was associated with serious infections in biologics-treated patients, but not non-biologic DMARD-treated patients. On the other hand, prednisolone at greater than 5 mg/day was associated with serious infections in both biologics-treated and non-biologics-treated patients. We show that there is not a significant difference between the incidence of serious infections between biologics group and non-biologics group in elderly RA patients (≧65 years) and that even very low-dose glucocorticoid use (prednisolone 1-4 mg/day) is a risk factor for serious infections in biologics-treated elderly RA patients.

T-bet inhibits innate lymphoid cell-mediated eosinophilic airway inflammation by suppressing IL-9 production.

BACKGROUND: Innate lymphoid cells (ILCs) are emerging subsets of immune cells that produce large amounts of cytokines upon cytokine and/or alarmin stimulation. Recent studies have shown that T-bet plays pivotal roles in the development of ILC3s and type 1 ILCs; however, the roles of T-bet in lung type 2 innate lymphoid cells (ILC2s) remain unknown. OBJECTIVE: We sought to determine the role of T-bet in ILC2-mediated airway inflammation. METHODS: The expression of T-bet in lung ILCs (defined as Thy1.2+ Lin- cells) was examined. The roles of T-bet in the development of lung ILC2s and airway inflammation induced by IL-33 administration were examined by using T-bet-deficient (T-bet-/-) mice. Gene expression profiles of T-bet-/- lung ILCs were analyzed by RNA sequencing. RESULTS: T-bet was expressed in lung ILC2s (defined as Thy1.2+ Lin- cells expressing ST2 or CD25) and IFN-γ enhanced its expression. Although the development of lung ILC2s at steady-state conditions was normal in T-bet-/- mice, IL-33-induced accumulation of lung ILC2s and eosinophilic airway inflammation were exacerbated in T-bet-/- mice. The exacerbated accumulation of ILC2s and eosinophilic airway inflammation by the absence of T-bet were evident even in a RAG2-/- background, suggesting that T-bet expressed in non-T/non-B population is involved in the suppression of IL-33-induced eosinophilic airway inflammation. Transcriptome analysis revealed that IL-9 expression in IL-33-stimulated lung ILCs was upregulated in T-bet-/- mice compared with that in wild-type mice. Importantly, neutralization of IL-9 markedly attenuated IL-33-induced accumulation of lung ILC2s and eosinophilic inflammation in T-bet-/- mice. CONCLUSIONS: T-bet suppresses IL-9 production from lung ILC2s and thereby inhibits IL-33-induced eosinophilic airway inflammation.

Dectin-1 Plays an Important Role in House Dust Mite-Induced Allergic Airway Inflammation through the Activation of CD11b+ Dendritic Cells.

It is well known that sensitization against fungi is closely associated with severity of asthma. Dectin-1 (gene symbol Clec7a), a C-type lectin receptor, recognizes the fungal cell wall component ß-glucan, as well as some component(s) in house dust mite (HDM) extract. However, the roles of Dectin-1 in HDM-induced allergic airway inflammation remain unclear. In this study, we used Dectin-1-deficient (Clec7a-/-) mice to examine whether Dectin-1 is involved in HDM-induced allergic airway inflammation. We found that HDM-induced eosinophil and neutrophil recruitment into the airways was significantly attenuated in Clec7a-/- mice compared with that in wild-type mice. In addition, HDM-induced IL-5, IL-13, and IL-17 production from mediastinum lymph node cells was reduced in HDM-sensitized Clec7a-/- mice. Dectin-1 was expressed on CD11b+ dendritic cells (DCs), an essential DC subset for the development of allergic inflammation, but not on CD103+ DCs, plasmacytoid DCs, or lung epithelial cells. Transcriptome analysis revealed that the expression of chemokine/chemokine receptors, including CCR7, which is indispensable for DC migration to draining lymph nodes, was decreased in Clec7a-/- DCs. In accordance with these results, the number of HDM-labeled CD11b+ DCs in mediastinum lymph nodes was significantly reduced in Clec7a-/- mice compared with wild-type mice. Taken together, these results suggest that Dectin-1 expressed on CD11b+ DCs senses some molecule(s) in HDM extract and plays a critical role in the induction of HDM-induced allergic airway inflammation by inducing the expression of chemokine/chemokine receptors in DCs.

SOCS3 Expressed in M2 Macrophages Attenuates Contact Hypersensitivity by Suppressing MMP-12 Production.

Numerous studies have clarified the immunological mechanisms of contact hypersensitivity (CHS). In addition, we have recently shown that M2 macrophages play key roles in the development of CHS by producing matrix metalloproteinase-12 (MMP-12). However, regulatory mechanisms of the elicitation phase in CHS remain largely unknown. To determine the roles of suppressor of cytokine signaling (SOCS) family members in M2 macrophages in the regulation of CHS, we investigated the expression of SOCS family members in M2 macrophages at the inflammatory sites of CHS. Transcriptome analysis revealed that among SOCS family members, SOCS3 was highly expressed in M2 macrophages at the site of CHS, and SOCS3 induction was reduced by IFN-? neutralization. 2,4-Dinitrofluorobenzene-induced CHS was significantly enhanced and prolonged in mice lacking SOCS3 expression in monocytes/macrophages (SOCS3(?/?) mice) compared with that in control mice. Importantly, expression of MMP-12 in M2 macrophages was significantly increased in SOCS3(?/?) mice at the site of CHS, and deletion of the MMP-12 gene reduced the exacerbated CHS in SOCS3(?/?) mice. Finally, IFN-? inhibited IL-4-induced MMP-12 expression in a SOCS3-dependent manner. Taken together, these results suggest that SOCS3 expressed in M2 macrophages is involved in the attenuation and/or resolution of CHS, presumably by suppressing MMP-12 production.

Dectin-2 promotes house dust mite-induced T helper type 2 and type 17 cell differentiation and allergic airway inflammation in mice.

The fact that sensitization against fungi is closely related to the severity of asthma suggests that immune systems recognizing fungi are involved in the pathogenesis of severe asthma. Recently, Dectin-2 (gene symbol, Clec4n), a C-type lectin receptor, has been shown to function as not only a major pattern-recognition receptor for fungi, but also a receptor for some components of house dust mite (HDM) extract, a major allergen for asthma. However, the roles of Dectin-2 in the induction of HDM-induced allergic airway inflammation remain largely unknown. Our objective was to determine the roles of Dectin-2 in HDM-induced allergic airway inflammation. We examined the roles of Dectin-2 in the induction of HDM-induced T helper (Th) 2 and Th17 cell differentiation and subsequent allergic airway inflammation by using Clec4n-deficient (Clec4n(-/-)) mice. We also investigated Dectin-2-expressing cells in the lung and their roles in HDM-induced allergic airway inflammation. Clec4n(-/-) mice showed significantly attenuated HDM-induced allergic airway inflammation and decreased Th2 and Th17 cell differentiation. Dectin-2 mRNA, together with Dectin-3 and Fc receptor-γ mRNAs, was expressed in CD11b(+) dendritic cells (DCs), but not in CD4(+) T cells or epithelial cells in the lung. CD11b(+) DCs isolated from Clec4n(-/-) mice expressed lower amounts of proinflammatory cytokines and costimulatory molecules, which could lead to Th2 and Th17 cell differentiation than those from wild-type mice. HDM-pulsed Clec4n(-/-) DCs were less efficient for the induction of allergic airway inflammation than HDM-pulsed wild-type DCs. In conclusion, Dectin-2 expressed on CD11b(+) DCs promotes HDM-induced Th2 and Th17 cell differentiation and allergic airway inflammation.

Roles of mast cells in the pathogenesis of inflammatory myopathy.

INTRODUCTION: In addition to the pivotal roles of mast cells in allergic diseases, recent data suggest that mast cells play crucial roles in a variety of autoimmune responses. However, their roles in the pathogenesis of autoimmune skeletal muscle diseases have not been clarified despite their distribution in skeletal muscle. Therefore, the objective of this study is to determine the roles of mast cells in the development of autoimmune skeletal muscle diseases. METHODS: The number of mast cells in the affected muscle was examined in patients with dermatomyositis (DM) or polymyositis (PM). The susceptibility of mast cell-deficient WBB6F1-Kit(W)/Kit(Wv) mice (W/W(v) mice) to a murine model of polymyositis, C protein-induced myositis (CIM), was compared with that of wild-type (WT) mice. The effect of mast cell reconstitution with bone marrow-derived mast cells (BMMCs) on the susceptibility of W/W(v) mice to CIM was also evaluated. RESULTS: The number of mast cells in the affected muscle increased in patients with PM as compared with patients with DM. W/W(v) mice exhibited significantly reduced disease incidence and histological scores of CIM as compared with WT mice. The number of CD8⁺ T cells and macrophages in the skeletal muscles of CIM decreased in W/W(v) mice compared with WT mice. Engraftment of BMMCs restored the incidence and histological scores of CIM in W/W(v) mice. Vascular permeability in the skeletal muscle was elevated in WT mice but not in W/W(v) mice upon CIM induction. CONCLUSION: Mast cells are involved in the pathogenesis of inflammatory myopathy.

Tumor suppressor p53 inhibits systemic autoimmune diseases by inducing regulatory T cells.

The tumor suppressor p53 plays a central role in tumor suppression by inducing apoptosis, cell cycle arrest, senescence, and DNA repair. In addition to the antitumor functions of p53, accumulating evidence using systemic p53-deficient mice suggests that p53 suppresses autoimmunity. However, it remains unknown how p53 suppresses autoimmunity. In this study, we generated T cell-specific p53-deficient mice (CD4-Cre p53(fl/fl) mice, or p53 conditional knockout [cKO] mice) and found that aged p53-cKO mice spontaneously developed inflammatory lesions in various organs, including lung, liver, stomach, thyroid gland, submandibular gland, and kidney. Additionally, anti-nuclear Abs and autoantibodies against gastric parietal cells were detected in p53-cKO mice but not in control p53(fl/fl) mice (p53 wild-type mice). Importantly, the number of Foxp3(+)CD4(+) regulatory T cells (Tregs) in the spleen and lung as well as in vitro differentiation of induced Tregs was significantly reduced in p53-cKO mice as compared with that in p53 wild-type mice. Regarding the mechanisms underlying p53-mediated Treg induction, p53 enhanced the transcription of Foxp3 by binding to the promoter and the conserved noncoding DNA sequence-2 of the Foxp3 gene. Taken together, these results suggest that p53 expressed in T cells functions as a suppressor for autoimmunity by inducing Treg differentiation.

[18F]FDG uptake in proximal muscles assessed by PET/CT reflects both global and local muscular inflammation and provides useful information in the management of patients with polymyositis/dermatomyositis.

OBJECTIVE: This study aimed to determine whether [(18)F]fluorodeoxyglucose-PET/CT ([(18)F]FDG-PET/CT) discriminates PM/DM from non-muscular diseases and also whether FDG uptake in proximal muscles reflects the activity and severity of muscular inflammation in PM/DM. METHODS: Twenty treatment-naïve PM/DM patients who underwent [(18)F]FDG-PET/CT were retrospectively identified by reviewing medical records. The same number of age- and sex-matched control patients with non-muscular diseases were also identified. Standardized uptake value (SUV) was calculated for each of the seven proximal muscles. For patient-based assessment, mean proximal muscle SUV was calculated by averaging the SUVs for these proximal muscles bilaterally. RESULTS: Mean proximal muscle SUVs were significantly greater in PM/DM patients than in control patients (median 1.05 vs 0.69, P < 0.001). Mean proximal muscle SUVs significantly correlated with mean proximal manual muscle test scores (ρ = 0.49, P = 0.028) and serum levels of creatine kinase (ρ = 0.54, P = 0.015) and aldolase (ρ = 0.64, P = 0.002). Furthermore, SUVs in proximal muscles from which biopsy specimens were obtained significantly correlated with histological grade for inflammatory cell infiltration (ρ = 0.66, P = 0.002). CONCLUSION: Our results suggest that [(18)F]FDG-PET/CT is useful in the diagnosis of PM/DM when inflammation in proximal muscles is globally assessed with quantitative measurements. Our results also indicate that local FDG uptake in a proximal muscle reflects the activity of inflammation in the same muscle and provides useful information in determining the region for muscle biopsy.

Tumor suppressor p53 functions as a negative regulator in IgE-mediated mast cell activation.

Mast cells are known to play a pivotal role in allergic diseases such as allergic rhinitis, asthma, and atopic dermatitis by releasing granules containing histamine, LTC4, and other preformed chemical mediators. Previous reports have demonstrated that IKK2 (also called IKKß), a central intracellular component of NF-κB activation pathways, plays a critical role in IgE-mediated degranulation of mast cells and anaphylaxis in mice. In this study, we show that protein levels of tumor suppressor p53 are up-regulated upon IgE-mediated activation in mast cells and lack of p53 results in enhanced responses in both early and late phase anaphylaxis. p53 inhibits not only the catalytic activity of IKK2 presumably through the modulation of glycosylation but also p65 (RelA)-mediated transactivation. Our findings are the first to demonstrate that p53 functions as a negative regulator in mast cells.

STAT4 is required for IFN-ß-induced MCP-1 mRNA expression in murine mast cells.

BACKGROUND: Mast cells are immunocompetent cells that are found in almost all tissues and function as sentinels of immune responses. Recently, it has been shown that mast cells play significant roles in innate immune responses. However, it is still largely unknown whether signal transducers and activators of transcription 4 (STAT4), one of the STAT proteins under type I IFN signaling, is involved in type I IFN-mediated gene expression in mast cells. METHODS: We investigated the role of STAT4 in IFN-ß-induced gene expression in mast cells by using STAT4-deficient (STAT4(-/-)) bone marrow-derived mast cells (BMMCs). RESULTS: STAT4 was expressed in BMMCs and activated in response to IFN-ß but not to IL-12 or IL-23. The development of BMMCs as well as IgE-induced degranulation of BMMCs was normal in STAT4(-/-) mice. On the other hand, while IFN-ß-induced mRNA expression of interferon-induced protein with tetratricopeptide repeats 1 (IFIT-1), protein kinase interferon-inducible double stranded RNA dependent (PKR), and myxovirus resistance 1 (Mx1) was similar between STAT4(-/-) BMMCs and wild-type (WT) BMMCs, IFN-ß-induced MCP-1 mRNA expression was severely diminished in STAT4(-/-) BMMCs as compared with WT BMMCs. CONCLUSIONS: STAT4 plays an essential role in IFN-ß-induced MCP-1 mRNA expression in mast cells.

Toxic epidermal necrolysis with severe hyperbilirubinemia: complete re-epithelialization after bilirubin reduction therapies.

Toxic epidermal necrolysis is a life-threatening skin disorder, and its mortality rate is estimated to be approximately 20-30%. It is characterized that more than 30% of the skin surface is eroded, however, skin lesions are usually re-epithelialized within 2-3 weeks. Previously, we reported a fatal case of toxic epidermal necrolysis with hyperbilirubinemia, and more than 60% of body surface areas had been eroded for 9 weeks. For the reason of delayed re-epithelialization, we hypothesized that hyperbilirubinemia was the culprit because bilirubin damaged cultured keratinocytes in vitro. In this case, we had an opportunity to treat another case of toxic epidermal necrolysis with severe hyperbilirubinemia. In order to reduce serum bilirubin levels, we performed bilirubin adsorption therapies, and skin lesions were successfully re-epithelialized within 4 weeks. Though further studies are required, we considered that bilirubin adsorption therapies are worth trying for toxic epidermal necrolysis with hyperbilirubinemia, especially for the cases suffering from delayed re-epithelialization.