Christian D. Sadik

Epidermolysis Bullosa Acquisita: From Pathophysiology to Novel Therapeutic Options.

Epidermolysis bullosa acquisita (EBA) is a prototypic organ-specific autoimmune disease induced by autoantibodies to type VII collagen causing mucocutaneous blisters. In the inflammatory (bullous pemphigoid-like) EBA variant, autoantibody binding is followed by a lesional inflammatory cell infiltration, and the overall clinical picture may be indistinguishable from that of bullous pemphigoid, the latter being the most common autoimmune bullous disease. The last decade witnessed the development of several mouse models of inflammatory EBA that facilitated the elucidation of the pathogenesis of autoantibody-induced, cell-mediated subepidermal blistering diseases and identified new therapeutic targets for these and possibly other autoantibody-driven disorders.

Severe bullous pemphigoid associated with pembrolizumab therapy for metastatic melanoma with complete regression.

Bullous pemphigoid (BP) is considered to be a humorally mediated autoimmune disease, but autoreactive T‐cells and T‐regulatory cells (Tregs) have also been implicated in this disease. Tregs and the programmed death‐1 (PD‐1) : programmed death ligand (PD‐L) pathway are both critical in terminating immune response, and elimination of either can result in breakdown of tolerance and development of autoimmunity. We report a patient with metastatic malignant melanoma (MM), who underwent pembrolizumab (anti‐PD‐1) therapy following unsuccessful treatment with ipilimumab [anti‐cytotoxic T‐lymphocyte‐associated protein (CTLA)‐4]. The patient developed BP with increasing serum titres of anti‐BP180 IgG autoantibodies and increasing disease severity during pembrolizumab therapy. High doses of corticosteroids and methotrexate were needed to control the BP. Following the termination of pembrolizumab therapy, imaging showed complete regression of all metastatic sites. This result may indicate a crucial role for T‐cell suppressive activity in controlling and preventing BP.

Leukotrienes orchestrating allergic skin inflammation

Leukotrienes constitute a group of lipid mediators, which may be subdivided into two groups, with leukotriene B4 on the one hand and cysteinyl leukotrienes on the other. Although leukotrienes are abundantly expressed in skin affected by diverse chronic inflammatory diseases, including atopic dermatitis, psoriasis, pemphigus vulgaris and bullous pemphigoid, their pathological roles in these diseases have remained elusive. Recent data now reveal that both leukotriene B4 and cysteinyl leukotrienes are indispensable in the pathogenesis of atopic dermatitis, with leukotriene B4 initiating the recruitment of inflammatory cells, particularly neutrophils and TH2 cells into the skin, and cysteinyl leukotrienes later inducing characteristic structural alterations of chronically affected skin, specifically skin fibrosis and keratinocyte proliferation. Thus, these results reveal a sequential cooperation of LTB4 and cysteinyl leukotrienes to initiate and perpetuate allergic skin inflammation. These new insights highlight leukotrienes as promising therapeutic targets in allergic skin inflammation and should encourage more research into the role of leukotrienes in other inflammatory skin diseases.

The Leukotriene B4 and its Receptor BLT1 Act as Critical Drivers of Neutrophil Recruitment in Murine Bullous Pemphigoid-Like Epidermolysis Bullosa Acquisita

Recruitment of neutrophils and eosinophils into the skin is a hallmark of pemphigoid diseases. The molecular cues regulating granulocyte recruitment into the skin and the individual contributions of neutrophils and eosinophils to pemphigoid diseases are, however, poorly understood. The lipid mediator leukotriene B4 (LTB4) is a potent granulocyte chemoattractant and is abundant in the skin blister fluid of bullous pemphigoid (BP) patients, but its pathogenic significance is unknown. Using mouse models of BP-like epidermolysis bullosa acquisita and of BP, we show that LTB4 and its receptor BLT1 act as critical drivers of neutrophil entry into the skin upon antibody deposition at the dermal-epidermal junction. Mice deficient in 5-lipoxygenase, a key enzyme in LTB4 biosynthesis, or in BLT1 exhibited dramatic resistance to neutrophil recruitment and, consequently, skin inflammation. Accordingly, liquid chromatography-mass spectrometry, used to comprehensively profile lipid mediator generation in the first 48 hours after antibody deposition, showed a pronounced parallel increase in LTB4 and in neutrophils in the skin. Subsequent mechanistic studies in BP-like epidermolysis bullosa acquisita uncovered that neutrophils are necessary for skin inflammation, whereas eosinophils are dispensable, thus identifying neutrophils as major culprits of blister formation. Our results highlight LTB4/BLT1 as absolutely critical drivers of murine pemphigoid disease-like skin inflammation.

Meeting Report of the Pathogenesis of Pemphigus and Pemphigoid Meeting in Munich, September 2016

Autoimmune blistering diseases are a heterogeneous group of about a dozen complex disorders that are characterized by intraepidermal (pemphigus) and subepidermal blistering (pemphigoid diseases and dermatitis herpetiformis). The Pathogenesis of Pemphigus and Pemphigoid Meeting, organized by the Departments of Dermatology in Lübeck and Marburg and the Institute of Anatomy and Cell Biology, Munich, was held in September 2016 in Munich. The meeting brought together basic scientists and clinicians from all continents dedicating their work to autoimmune blistering diseases. Considerable advances have been made in describing incidences and prevalences of these diseases and linking comorbidities with autoantibody reactivities and clinical variants, for example, dipeptidyl peptidase-IV inhibitor-associated noninflammatory bullous pemphigoid. Although new entities are still being described, diagnosis of most autoimmune blistering diseases can now be achieved using standardized and widely available serological test systems. Various experimental mouse models of pemphigus and pemphigoid disease are increasingly being used to understand mechanisms of central and peripheral tolerance and to evaluate more specific treatment approaches for these disorders, such as molecules that target autoreactive T and B cells and anti-inflammatory mediators, that is, dimethyl fumarate, phosphodiesterase 4, and leukotriene B4 inhibitors in pemphigoid disorders, and chimeric antigen receptor T cells in pemphigus. Very recent experimental data about the immunopathology and the determinants of autoantibody formation and keratinocyte susceptibility in pemphigus were discussed. With regard to cellular mechanisms leading to the loss of cell-cell adhesion, new ideas were shared in the field of signal transduction. Major steps were taken to put the various partly contradictory and controversial findings about the effects of pemphigus autoantibodies and other inflammatory mediators into perspective and broaden our view of the complex pathophysiology of this disease. Finally, two investigator-initiated multicenter trials highlighted doxycycline and dapsone as valuable medications in the treatment of bullous pemphigoid.

Uncoupling protein 2 protects mice from aging.

Uncoupling protein (UCP) 2 is a mitochondrial transporter protein that plays various roles in cellular metabolism, including the glucose and lipid metabolism. Polymorphisms in UCP2 are associated with longevity in humans. In line with this, mice carrying the UCP2 transgene under the control of hypocretin promoter were reported to have an extended lifespan, while, conversely, mice deficient in Ucp2 demonstrated a significantly shorter lifespan. In this study, we examined the phenotype of aging in a large colony of Ucp2-deficient (Ucp2(-/-)) mice on the molecular level. We have found that the significantly shorter lives of Ucp2(-/-) mice is the result of an accelerated aging process throughout their entire lifespan. Thus, Ucp2(-/-) mice not only earlier gained sexual maturity, but also earlier progressed into an aging phenotype, reflected by a decrease in body weight, increased neutrophil numbers, and earlier emergence of spontaneous ulcerative dermatitis. Intriguingly, on the molecular level this acceleration in aging predominantly driven by increased levels of circulating IGF-1 in Ucp2(-/-) mice, hinting at a crosstalk between UCP2 and the classical Insulin/IGF-1 signaling aging pathway.

Pemphigoid gestationis: Toward a better understanding of the etiopathogenesis

Pemphigoid gestationis (PG) is the only autoimmune disease exclusively emerging in pregnancy. It belongs to the pemphigoid group of disorders, a class of autoimmune blistering skin diseases featuring an immune response against different hemidesmosomal proteins. PG is caused by a break of immunotolerance against the hemidesmosomal protein BP180. Several lines of evidence suggest that this break of immunotolerance is linked to specific maternal major histocompatibility complex (MHC) class II gene variants and aberrant expression of MHC class II molecules in the placenta. The close time association of the emergence of PG with pregnancy and the obviously very short period required from the initial break of immunotolerance to the onset of skin inflammation set PG into a unique position among autoimmune diseases in view of the fact that, for other autoimmune diseases, the time and site of the break of immunotolerance are usually vastly elusive and the period of silent disease can only be speculated on. In this review we highlight the features of PG and summarize current knowledge about its pathogenesis. We believe that this disease offers the best opportunity to elucidate comprehensively all phases of the pathogenesis of an autoantibody-driven disease.

Current treatments and developments in pemphigoid diseases as paradigm diseases for autoantibody-driven, organ-specific autoimmune diseases

Pemphigoid diseases constitute a group of difficult-to-treat, remitting-relapsing autoimmune skin diseases. They are autoantibody-driven diseases with well-defined autoantigens in the hemidesmosomal complex at the dermal-epidermal junction (DEJ). Autoantibody deposition initiates the recruitment of granulocytes to the DEJ, where these cells degrade the hemidesmosomal complex, disrupting dermal-epidermal adherence, which clinically manifests as blisters and erosions. Due to their well-defined autoantigens and the location at the body surface, allowing the direct observation of inflammation throughout its course, pemphigoid diseases are excellent paradigm diseases to study the pathomechanisms of autoantibody-driven diseases. Current treatments of pemphigoid diseases largely rely on systemic immunosuppression despite the restriction of inflammation to the skin. The iatrogenic immunosuppression may contribute to the high 1-year mortality rate in pemphigoid diseases. Thus, the overall survival does not depend on the extent of skin lesions before treatment, but depends on whether topical or systemic glucocorticoid application is initially used. Systemic glucocorticoid application is linked to higher mortality than topical application, illustrating that systemic immunosuppression can harm the overall prognosis and that immunomodulatory treatment strategies are required. New mouse models of pemphigoid diseases have been instrumental in approaching the introduction of novel immunomodulatory therapies in the treatment of autoimmune diseases.

Automated direct immunofluorescence analyses of skin biopsies

Diagnosis of autoantibody‐ and immune complex‐induced skin diseases is primarily based on direct immunofluorescence (DIF) microscopy. DIF staining is usually performed manually and, therefore, is labor intensive. The quality of immunohistochemical results considerably depends on the experience of the person conducting the tests. The novel EUROTide™ technique in combination with the biochip‐based system EUROPath represents a new technology for automation of DIF staining.

The genetic difference between C57Bl/6J and C57Bl/6N mice significantly impacts Aldara™-induced psoriasiform dermatitis

Since its first description in 2009,1 the AldaraTM (MEDA Pharma GmbH, Bad Homburg, Germany)-induced psoriasiform dermatitis (AIPD) model has become a most commonly used mouse model of plaque psoriasis. It is mostly conducted in the C57Bl/6 mouse strain. Two substrains of this mouse strain, C57Bl/6J and C57Bl/6N, are in parallel widely used for research purposes. The two substrains are phenotypically identical but genetically differ by 34 SNPs, two indels and 15 gene variants that overlap a gene.2–4 Notably, gene knockout and transgenic mice on the C57Bl/6 background are often held on an intermediate genotype between the two substrains due to incomplete backcrossing after genetic manipulation. This issue has become even more common in recent years with the International Knockout Mouse Consortium’s (IKMC) decision to preferentially generate genetic knockouts in C57Bl/6N embryonic stem cells,4 while, in contrast, most investigators still preferably use C57Bl/6J mice.