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Pemphigus vulgaris is an autoimmune blistering disease caused by IgG targeting desmoglein 3 (Dsg3), an adhesion molecule of keratinocytes. Anti-Dsg3 IgG production is prevented in healthy individuals, but it is unclear how Dsg3-specific B cells are regulated. To clarify the immunological condition regulating Dsg3-specific B cells, a pathogenic anti-Dsg3 Ig (AK23) knock-in mouse was generated. AK23 knock-in B cells developed normally without undergoing deletion or acquiring an anergic phenotype in vivo. The knock-in B cells showed Ca2+ influx upon IgM cross-linking and differentiated into AK23-IgG+ B cells after LPS and IL-4 stimulation in vitro that induced a pemphigus phenotype after adoptive transfer into Rag2−/− mice. However, the knock-in mouse itself produced AK23-IgM but little IgG without blisters in vivo. Dsg3 immunization and skin inflammation caused AK23-IgG production and a pemphigus phenotype in vivo. Furthermore, Fcgr2b deficiency or haploinsufficiency spontaneously induced AK23-IgG production and a pemphigus phenotype with poor survival rates in AK23 knock-in mice. To assess Fcgr2b involvement in Ig class-switch efficiency, postswitch transcripts of B cells were quantified and significantly higher in Fcgr2b−/− and Fcgr2b+/− mice than wild-type mice in a gene dose-dependent manner. Finally, RNA sequencing revealed reduced expression of FCGR2B and FcγRIIB-related genes in patient B cells. These results indicated that Dsg3-specific B cells do not spontaneously perform pathogenic class switching in vivo, and pemphigus phenotype induction was prevented under normal conditions. Attenuated FcγRIIB signaling is also one of the drivers for pathogenic class switching and is consistent with immunological features identified from clinical samples. This study unveiled a characteristic immune state silencing autoreactive B cells in mice.

A 6-month-old female beagle dog, assigned to the low-dose group in a toxicity study, was evaluated for compound toxicity, and spontaneous hyperadrenocorticism was suspected. The animal had an externally apparent distended abdomen on clinical examination upon arrival. Pre-dose clinical pathology showed slightly higher erythroid parameters and stress leukogram on hematology; plasma biochemistry showed higher total protein, gamma-glutamyl transferase, total cholesterol, and triglyceride levels than the reference data. On necropsy, a prominent increase in adipose tissues of the subcutis and abdomen and increased weight of the adrenal gland and liver were observed. Histopathology revealed diffuse hyperplasia of adrenocortical cells in the zona fasciculata and reticularis, cortical atrophy of the thymus, and abundant glycogen accumulation in the hepatocytes. These findings were incidental and not test-substance-related. Electron microscopy of the adrenocortical cells in the zona fasciculata revealed decreased typical translucent lipid droplets, increased electron-dense lipid droplets, and abundant smooth endoplasmic reticulum and lysosomes. Additionally, increased numbers of various sizes and forms of mitochondria with tubular, vesicular, or lamellar cristae compared to that of normal animals were observed. These ultrastructural characteristics of the adrenocortical cells suggested hyperfunction. The pre-dose plasma cortisol levels were slightly higher than those of other females assigned to the toxicity study, while plasma adrenocorticotropic hormone levels were within the normal range. These findings indicate that hyperadrenocorticism is a possible cause of the systemic changes in this case.

Background The thymus plays an essential role in removing autoreactive T cells. Autoantigen-expressing thymic epithelial cells (TECs) contribute to the tolerogenic process. The thymus transiently shrinks as an acute thymic involution (ATI) under various inflammatory conditions. However, whether ATI occurs during local skin inflammation remains unclear, as does its influence on thymic immune tolerance. Objective We investigated whether imiquimod-induced dermatitis causes ATI and impairs thymic immune tolerance against desmoglein 3 (Dsg3), an epidermal autoantigen of pemphigus vulgaris. Methods 5% imiquimod cream was applied daily, at 62.5 mg/day (high dose group) or 31.25 mg/day (low dose group), for 1 week on the back of wild-type mice, and to wild-type mice that had undergone bone-marrow transplantation from Dsg3-specific T-cell receptor (TCR) transgenic-Rag2−/− mice. Next, thymocytes, TECs and other immune cells were analyzed by flow cytometry. TEC-associated Dsg3 expression was also analyzed by immunofluorescence staining. Results Thymus weight and thymocyte number in all developmental stages decreased in a dose-dependent manner under imiquimod-induced dermatitis. The number of total TECs, specifically medullary, but not cortical, TECs, decreased in high and low dose groups. Accordingly, the number of Dsg3-experssing UEA-1+keratin 5+mTEC decreased in the thymus during imiquimod-induced dermatitis. Although Dsg3-sepcific transgenic thymocytes was usually deleted in the thymus under physiological condition by central tolerance, Dsg3-sepcific transgenic CD4+CD8− thymocytes significantly increased in number under imiquimod-induced dermatitis. Conclusion These findings indicate a crosstalk between skin and thymus in adult mice and suggest that skin inflammation may impair thymic tolerance to autoantigens, such as Dsg3.

Antigen-specific peripheral tolerance is crucial to prevent the development of organ-specific autoimmunity. However, its function decoupled from thymic tolerance remains unclear. We used desmoglein 3 (Dsg3), a pemphigus antigen expressed in keratinocytes, to analyze peripheral tolerance under physiological antigen-expression conditions. Dsg3-deficient thymi were transplanted into athymic mice to create a unique condition in which Dsg3 was expressed only in peripheral tissue but not in the thymus. When bone marrow transfer was conducted from high-avidity Dsg3-specific T cell receptor–transgenic mice to thymus-transplanted mice, Dsg3-specific CD4(+) T cells developed in the transplanted thymus but subsequently disappeared in the periphery. Additionally, when Dsg3-specific T cells developed in Dsg3(−/−) mice were adoptively transferred into Dsg3-sufficient recipients, the T cells disappeared in an antigen-specific manner without inducing autoimmune dermatitis. However, Dsg3-specific T cells overcame this disappearance and thus induced autoimmune dermatitis in Treg-ablated recipients but not in Foxp3-mutant recipients with dysfunctional Tregs. The molecules involved in disappearance were sought by screening the transcriptomes of wild-type and Foxp3-mutant Tregs. OX40 of Tregs was suggested to be responsible. Consistently, when OX40 expression of Tregs was constrained, Dsg3-specific T cells did not disappear. Furthermore, Tregs obtained OX40L from dendritic cells in an OX40-dependent manner in vitro and then suppressed OX40L expression in dendritic cells and Birc5 expression in Dsg3-specific T cells in vivo. Lastly, CRISPR/Cas9-mediated knockout of OX40 signaling in Dsg3-specific T cells restored their disappearance in Treg-ablated recipients. Thus, Treg-mediated peripheral deletion of autoreactive T cells operates as an OX40-dependent regulatory mechanism to avoid undesired autoimmunity besides thymic tolerance.

IL-27 is an immunoregulatory cytokine whose essential function is to limit immune responses. We found that the gene encoding cholesterol 25-hydroxylase (Ch25h) was induced in CD4(+) T cells by IL-27, enhanced by TGF-β, and antagonized by T-bet. Ch25h catalyzes cholesterol to generate 25-hydroxycholesterol (25OHC), which was subsequently released to the cellular milieu, functioning as a modulator of T cell response. Extracellular 25OHC suppressed cholesterol biosynthesis in T cells, inhibited cell growth, and induced nutrient-deprivation cell death without releasing high-mobility group box-1. This growth inhibitory effect was specific to actively proliferating cells with high cholesterol demand and was reversed when extracellular cholesterol was replenished. Interestingly, Ch25h expressing CD4(+) T cells that received IL-27 and TGF-β signals became refractory to 25OHC-mediated growth inhibition in vitro. Nonetheless, IL-27 treated T cells negatively affected viability of bystander cells in a paracrine manner, but only if the bystander cells were in the early phases of activation. In mouse models of skin inflammation due to autoreactive T cells or chemically induced hypersensitivity, genetic deletion of Ch25h or Il27ra led to worsened outcomes. Thus, Ch25h is an immunoregulatory metabolic switch induced by IL-27 and dampens excess bystander T effector expansion in tissues through its metabolite derivative, 25OHC. This study reveals regulation of cholesterol metabolism as a modality for controlling tissue inflammation and thus represents a mechanism underlying T cell immunoregulatory functions.

Autoimmune diseases are devastating conditions in which the immune system is directed against the host, leading to life-threatening destruction of organs. Although autoantigens are ill-defined in most autoimmune diseases, this is not the case in the skin. Autoimmune bullous diseases have been extensively studied with detailed characterization of autoantigens, the epitopes that are targeted, and the mechanisms of action that mediate autoimmune tissue destruction. Pemphigus is an autoimmune bullous disease caused by circulating IgG that targets two desmosomal proteins, desmoglein 1 and 3, which are crucial for cell–cell adhesion of keratinocytes. Binding of auto-antibodies to desmogleins impairs keratinocyte adhesion, leading to severe blistering disease. Mouse models that recapitulate the human disease have been instrumental in elucidating the detailed pathophysiology. Taking advantage of the fact that desmogleins are specifically targeted in pemphigus, studying humoral and cellular autoimmunity against these autoantigens provides us with an opportunity to understand not only the effector mechanisms of B and T cells in mediating pathology but also how autoreactive lymphocytes are regulated during development in the thymus and post-development in the periphery. This review introduces pemphigus and its subtypes as prototypic autoimmune diseases from which recent basic and translational developments should provide insight into how autoimmunity develops.

Although immunoglobulin class-switching is essential for humoral immunity, its role in B-cell immune tolerance remains unclear. Pemphigus vulgaris is an autoimmune blistering disease caused by IgG targeting desmoglein 3, an adhesion molecule of keratinocytes. In this study, we generated knock-in mice that express anti-Dsg3 AK23 autoantibodies. Knock-in B cells developed normally in vivo and showed Ca2+ influx upon IgM cross-linking in vitro. The mice predominantly produced circulating AK23 IgM but little IgG antibodies. Although no IgG deposition or blister formation was observed in Dsg3-bearing tissues, Dsg3 immunization forced to induce pemphigus phenotype after class-switching to IgG in vivo. Transcriptomic analysis revealed that FCGR2B and FcγRIIB-related genes were downregulated in B cells from peripheral blood of pemphigus patients. Indeed, in AK23 knock-in mice, Fcgr2b deficiency or haploinsufficiency spontaneously led to class-switching, AK23 IgG production, and pemphigus phenotype development. Thus, inhibition of pathogenic class-switching is a crucial tolerogenic process to prevent pemphigus onset, where attenuated FcγRIIB signaling is one of the key predispositions to break this tolerogenic state.

Nail patella syndrome is a autosomal dominant disorder caused by a genetic alteration in LMX1B. We identified a novel heterozygous in-frame indel mutation of LMX1B in a family of Nail patella syndrome. Impaired transcriptional activity but not dominant negative effect of mutant LMX1B were revealed using a transcriptional reporter assay, indicating that the mutation caused nail patella syndrome in this family via haploinsufficiency of the transcriptional activity of LMX1B.

The pathological mechanisms and immunological kinetics of drug-induced hypersensitivity syndrome (DIHS), including the relevance of interleukin (IL)-6, remain unclear. We report a case of drug adverse reaction that does not fulfill the diagnostic criteria of DIHS but mimics its characteristic features. Because the patient was under anti-IL-6 therapy at the onset, some symptoms typically seen in DIHS were absent, such as fever and leukocyte count abnormalities. However, the characteristic features of DIHS were clearly observed in the subsequent course, including the repeated recurrence of skin rash, prolonged liver dysfunction and reactivation of herpes viruses. This case suggested that IL-6 role at the onset is not a main factor to determine the subsequent pathomechanism of DIHS and attention should be paid to the preceding therapy for achieving accurate diagnosis.

Both acquired perforating dermatosis (APD) and bullous pemphigoid (BP) are associated with a wide variety of systemic and cutaneous disorders [1, 2]. However, coexistence of APD and BP has never been reported. Herein, we describe three patients with coexisting BP and APD. The patients had several common features, suggesting that this condition is a new and unique clinical presentation associated with BP.Patient 1 was a 65-year-old male who presented with a three-month history of pruritic skin lesions [...]