Pseudolymphoma on the face involving the conjunctiva

Pseudolymphoma is a benign lymphoproliferative disorder characterized by an excessive response of inflammatory cells to various triggers. To the best of our knowledge, this is the first report of pseudolymphoma occurring concurrently on the face and the conjunctiva.

Detection of a natural antibody targeting the shed ectodomain of BP180 in mice

BACKGROUND

Pemphigoid diseases are characterized by subepidermal blister formation accompanied by autoantibodies targeting skin component molecules, such as BP180. It is suggested that an epitope-phenotype correlation exists among autoantibodies recognizing BP180. However, it is unclear which regions of BP180 are likely targets for autoantibodies.

OBJECTIVE

To elucidate the portions of BP180 where antibodies tend to react under the breakdown of immune tolerance.

METHODS

We immunized mice with full-length mouse BP180 (mBP180) to produce anti-mBP180 antibodies. Using the immunized mice, hybridoma cells were established to produce anti-mBP180 antibodies. We analyzed the characteristics of the anti-mBP180 antibodies that were produced in terms of epitopes, immunoglobulin subclasses, and somatic hypermutations.

RESULTS

Hybridoma cells derived from immunized mice with full-length mBP180 produced antibodies targeting the intracellular domain (IC) and the shed ectodomain (EC) of mBP180. Using the domain-deleted mBP180 recombinant protein, we revealed that monoclonal anti-mBP180 EC antibodies react to neoepitopes on the 13th collagenous region of cleaved mBP180, which corresponds to the epitopes of linear IgA bullous dermatosis antibodies in human BP180. Furthermore, the subclasses of these antibodies could be distinguished by epitope: The subclass of the anti-mBP180 IC monoclonal antibodies was IgG, whereas that of the anti-mBP180 EC antibodies was IgM. Of note, a clone of these IgM mBP180 EC antibodies was a germline antibody without somatic hypermutation, which is also known as a natural antibody.

CONCLUSION

These data suggest that mice potentially have natural antibodies targeting the neoepitopes of cleaved mBP180 EC.

Native autoantigen complex detects pemphigoid autoantibodies

Pemphigoid diseases are a group of autoimmune disorders characterized by subepidermal blistering in the skin and mucosa. Among them, mucous membrane pemphigoid (MMP) autoantibodies are characterized by targeting multiple molecules in the hemidesmosomes, including collagen XVII, laminin-332, and integrin a6/β4. Traditionally, recombinant proteins of the autoantigens have been employed to identify circulating autoantibodies by immune assays. However, developing an efficient detection system for MMP autoantibodies has been challenging because the autoantibodies have heterogeneous profiles and the antibody titers are typically low. In this study, we introduce an ELISA that takes advantage of a native autoantigen complex rather than simple recombinant proteins. We generated HaCaT keratinocytes with a DDDDK-tag knocked in at the COL17A1 locus by CRISPR/Cas9-mediated gene editing. Immunoprecipitation using the DDDDK-tag isolated a native complex that contained full-length and processed collagen XVII and integrin α6/β4. Then, we used the complex proteins to prepare an ELISA system and enrolled 55 MMP cases to validate its diagnostic performance. The sensitivity and specificity of the ELISA for detecting MMP autoantibodies were 70.9% and 86.7%, respectively, far superior to those of conventional assays. In autoimmune diseases such as MMP, in which autoantibodies target various molecules, isolating the antigen-protein complexes can help establish a diagnostic system.

A Case of Anti-BP180-type Mucous Membrane Pemphigoid with IgG and IgA Autoantibodies Showing Distinct Reactivities

Dear Editor, Mucous membrane pemphigoid (MMP) is an autoimmune blistering disease characterized by erosive mucosal lesions mainly on the oral and ocular mucosae (1). We report a case of oral and ocular anti-BP180-type MMP with variable IgG and IgA reactivities and underlying dementia. An 84-year-old Japanese man presented with a 4-year history of erosions in the oral cavity and on the conjunctivae, with progressive vision impairment. The medical history included benign prostatic hyperplasia, cataract, sinusitis, and dementia. Physical examination revealed erosions and white atrophic scars along the gingival mucosa and on the hard palate (Figure 1, a, b). Conjunctival inflammation and corneal scarring were also observed only on the left eye (Figure 1, c, d). No lesions were observed on the skin or on any other mucosae. A skin biopsy from the patient's oral mucosa showed lymphocytic infiltration in the superficial dermis without apparent subepithelial blister. Direct immunofluorescence showed linear depositions of IgG, IgA, and C3 at the epithelial basement membrane zone (Figure 1, e-g). Circulating IgG and IgA autoantibodies were not detected by indirect immunofluorescence of normal human skin, while circulating IgA, but not IgG, autoantibodies were bound to the epidermal side of 1M NaCl-split normal human skin at 1:10 serum dilution (Figure 1, h, i). Commercially available IgG enzyme-linked immunosorbent assays (ELISAs) of BP180 NC16a domain, BP230, and type VII collagen (MBL, Nagoya, Japan) showed negative results. IgG and IgA immunoblotting analyses of six different antigen sources, including BP180 C-terminal domain recombinant protein, were all negative. However, ELISA of full-length BP180 was slightly positive for IgG antibodies (index = 5.79; cut-off <4.64). Immunoblotting analysis of full-length BP180 was negative for both IgG and IgA antibodies (Figure 1, j, k). Immunoblotting analysis of hemidesmosome-rich fraction was negative for both IgG and IgA antibodies to integrin β4 (Figure 1, l). Based mainly on the clinical and immunological findings, we established a diagnosis of MMP with IgG and IgA autoantibodies, likely reactive with BP180. Because the patient refused systemic treatments, we prescribed a mouth rinse sodium gualenate hydrate and eyedrops of fluorometholone and purified sodium hyaluronate, which did not improve the oral and ocular mucosal symptoms during the 8 month follow-up period (Figure 1, m, n). Both IgG and IgA autoantibodies in anti-BP180-type MMP tend to react with the C-terminal domain of BP180 (2), and IgG autoantibodies in 39.7% of MMP patients reactive with the epidermal side of split skin were reported to be positive with BP180 C-terminal domain (3). The full-length BP180 ELISA shows excellent sensitivity for diagnosing BP180-type MMP (4). The different IgG and IgA reactivities among various methods used in the present study may be attributed either to different methodologies (i.e., immunoblotting or ELISA) or to the different substrates, since BP180-type MMP targets various regions of BP180, including the NC16a domain, the C-terminal domain, and the intracytoplasmic region (5). Precise diagnosis for MMP by various immunological methods is critical, because urgent and extensive treatments are necessary for the ocular and laryngeal lesions, which may result in loss of eyesight and airway obstruction, respectively. Acknowledgments: We express our gratitude to Ms. Mako Mine and Dr. Daisuke Hayashi, Department of Dermatology, Osaka City University Graduate School of Medicine in Osaka, Japan for the HD-rich fraction immunoblotting analysis, and Dr. Yoshiaki Hirako, Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan for the preparation of the HD-rich fraction sample. This work was supported by JSPS KAKENHI Grant Number JP20k08684 and the Hirosaki University Research Support System.

Collagen XVII deficiency alters epidermal patterning

Vertebrates exhibit patterned epidermis, exemplified by scales/interscales in mice tails and grooves/ridges on the human skin surface (microtopography). Although the role of spatiotemporal regulation of stem cells (SCs) has been implicated in this process, the mechanism underlying the development of such epidermal patterns is poorly understood. Here, we show that collagen XVII (COL17), a niche for epidermal SCs, helps stabilize epidermal patterns. Gene knockout and rescue experiments revealed that COL17 maintains the width of the murine tail scale epidermis independently of epidermal cell polarity. Skin regeneration after wounding was associated with slender scale epidermis, which was alleviated by overexpression of human COL17. COL17-negative skin in human junctional epidermolysis bullosa showed a distinct epidermal pattern from COL17-positive skin that resulted from revertant mosaicism. These results demonstrate that COL17 contributes to defining mouse tail scale shapes and human skin microtopography. Our study sheds light on the role of the SC niche in tissue pattern formation.

Dipeptidyl peptidase 4 inhibitor-associated mucous membrane pemphigoid

Dipeptidyl peptidase 4 inhibitors (DPP-4i) are associated with an increased risk of developing bullous pemphigoid (BP) in patients with diabetes. Autoantibodies targeting epitopes on the processed BP180, 120-kDa (LAD-1), and 97-kDa (LABD97) linear immunoglobulin (Ig)A dermatosis antigens are the major autoantibodies in DPP-4i-associated BP. However, no case of mucous membrane pemphigoid (MMP) developing during treatment with DPP-4i has been reported. We report a case of MMP associated with DPP-4i. A man in his late 70s presented with oral mucous membrane erosion and a few blisters on his upper chest and back. He had used linagliptin for diabetes for over 1 year when he presented. The immunological characteristics were similar to DPP4i-associated BP: higher reactivity to LAD-1 and LABD97 than to the full-length BP180. The aphthae achieved remission after oral linagliptin was replaced with sitagliptin. However, 6 months later, the aphthae relapsed and any DPP-4i was discontinued. The aphthae disappeared, and now he is completely free from lesions associated with MMP. This case suggests that the DPP-4i may have shared roles in the production of IgG antibodies to LAD-1 or to LABD97 in the pathogenesis of DPP-4i-associated BP and MMP. Our case highlights the possibility of overlooking the mild MMP in DPP-4i-treated diabetes patients with mucosal lesions.

Neonatal Linear IgA Bullous Dermatosis Mediated by Breast Milk-Borne Maternal IgA

Importance

Neonatal linear immunoglobulin A (IgA) bullous dermatosis (LABD) is a rare disease that can be fatal when associated with respiratory failure. All previously reported cases of neonatal LABD have been in newborns with healthy asymptomatic mothers, and the pathogenic IgA was of unknown origin.

Objective

To clarify the origin of IgA associated with LABD in neonates born of healthy asymptomatic mothers.

Design, Setting, and Participants

This case study analyzed the laboratory findings of a single breast-fed newborn male with neonatal LABD admitted to the Keio University Hospital in Tokyo and his healthy asymptomatic mother. The healthy newborn developed life-threatening blisters and erosions of the skin and mucous membranes on day 4 after birth. Blood serum, skin, and maternal breast milk were examined for IgA autoantibodies.

Main Outcomes and Measures

Histopathologic and immunofluorescence analyses of specimens (serum, skin, and breast milk) from the patient and his mother.

Results

Histopathologic evaluation of the newborn's skin revealed subepidermal blisters with neutrophil infiltrates, and immunofluorescence testing showed linear IgA deposition along the basement membrane zone (BMZ), which lead to the diagnosis of neonatal LABD. Indirect immunofluorescence using normal human skin after treatment with 1-mol/L sodium chloride showed the patient to have circulating IgA binding to the dermal side of BMZ. Immunohistochemical staining proved the deposition of secretory IgA in the neonatal skin by demonstrating the presence of J chain-not been seen in other LABD cases-indicating that the autoantibodies producing the blisters were derived from the maternal breast milk. Although no circulating IgA against the skin was detected in mother's sera, the breast milk contained IgA that reacted with the dermal side of the BMZ. No new blister formation was observed after cessation of breastfeeding.

Conclusions and Relevance

The results of this case study suggest a passive transfer of pathogenic IgA to a newborn from an asymptomatic mother via breast milk. In prior reports, no serum from asymptomatic mothers of newborns with LABD had IgA autoantibodies binding to skin components; however, in this case, we found that the maternal breast milk contained IgA autoantibodies associated with neonatal LABD. In neonatal LABD, maternal breast milk should be examined for IgA autoantibodies and breast milk feeding should be discontinued as soon as neonatal LABD is suspected.

A Case of Possible Concurrence of Dermatitis Herpetiformis and Linear Immunoglobulin A / Immunoglobulin G Bullous Dermatosis

Dear Editor, Linear immunoglobulin (Ig) A bullous dermatosis (LABD), one subtype of subepidermal autoimmune bullous skin diseases (AIBDs), is characterized by linear deposit of only IgA along the basement membrane zone (BMZ) on direct immunofluorescence (DIF) (1,2). Patients showing linear deposits of both IgA and IgG are diagnosed with linear IgA/IgG bullous dermatosis (LAGBD) (3,4). Dermatitis herpetiformis (DH) is another type of subepidermal AIBD characterized by clinically pruritic erythematous skin lesions with vesicles on the elbows, knees, and buttocks with granular IgA deposits of IgA by DIF (5). In this study, we report a Japanese case of a patient who showed possible concurrence of DH and LAGBD based on clinical, histological, and immunological findings. A 72-year-old Japanese man who had a past history of dyslipidemia and resected lung cancer but was not taking any medicines, presented with a one-year history of blistering skin lesions. Physical examination revealed erythemas and peripherally arranged vesicles and erosions on the bilateral elbows, knees, and the buttock (Figure 1, a-c). Mucous membranes were not involved. The results of all laboratory tests were within normal ranges, except for increased serum IgA level 351 mg/dL (normal ranges; 46-260 mg/dL). Skin biopsy histopathologically showed subepidermal blisters infiltrated with neutrophils and eosinophils (Figure 1, d). DIF showed deposits of IgG, IgA, and complement component 3 along the BMZ mainly in granular but partially in a linear pattern (Figure 1, e-g). Circulating IgG (Figure 1, h) and IgA (Figure 1, i) autoantibodies were not detected by indirect immunofluorescence (IIF) of normal skin, however, circulating IgA (Figure 1, j) but not IgG (Figure 1, k) antibodies were bound to both the epidermal and dermal sides by IIF of 1M NaCl-split normal skin. Commercially available enzyme-linked immunosorbent assays (ELISAs) for BP180 NC16a domain, BP230, and type Vll collagen (MBL, Nagoya, Japan), showed negative results for both IgG and IgA antibodies. IgG in-house ELISA for full length BP180 was also negative. IgG and IgA immunoblotting analyses of different antigen sources, including normal human epidermal and dermal extracts, recombinant proteins of NC16a, and C-terminal domains of BP180 region, BP230, purified laminin 332, and concentrated culture supernatant of HaCaT cells for LAD-1, were all negative. IgA ELISAs of tissue- and epidermal-transglutaminases were negative (1.92 AU/mL and 20.98 AU/mL, respectively; normal range <22.0 AU/mL). The patient was successfully treated with only topical corticosteroids with occasional mild local relapses. Japanese DH is different from European DH in some respects, i.e., DH is very rare in Japan due to genetic/HLA difference, absence of celiac disease, and frequent fibrillar IgA deposition in DIF. Therefore, we believe that this case is interesting as a rare Japanese DH case with complicated conditions. The clinical and immunochemical characteristics in the present case were compatible for both DH and LAGBD. Clinical features of vesicles on erythemas on the knees and buttock suggested DH, while histopathological features were compatible with LAGBD but also with DH, DIF results suggested both LAGBD and DH, and the results of IIF of 1M NaCl-split skin suggested LAGBD. All biochemical studies for autoantigens were negative, which suggested DH. However, autoantigens are not clearly detected in many LAGBD cases, either. IgA anti-epidermal transglutaminase antibody, a DH marker, was negative, but the titer was relatively high but within normal range. Therefore, we considered that this case might have developed DH and LAGBD concurrently. However, there may be two other possibilities: [1] this case was DH and non-pathogenic circulating autoantibodies were secondary production, and [2] LAGBD cases may sometimes show granular-linear BMZ deposition of IgG and IgA. Future studies on similar cases are needed to clarify our speculations.

Hair follicle stem cell progeny heal blisters while pausing skin development

Injury in adult tissue generally reactivates developmental programs to foster regeneration, but it is not known whether this paradigm applies to growing tissue. Here, by employing blisters, we show that epidermal wounds heal at the expense of skin development. The regenerated epidermis suppresses the expression of tissue morphogenesis genes accompanied by delayed hair follicle (HF) growth. Lineage tracing experiments, cell proliferation dynamics, and mathematical modeling reveal that the progeny of HF junctional zone stem cells, which undergo a morphological transformation, repair the blisters while not promoting HF development. In contrast, the contribution of interfollicular stem cell progeny to blister healing is small. These findings demonstrate that HF development can be sacrificed for the sake of epidermal wound regeneration. Our study elucidates the key cellular mechanism of wound healing in skin blistering diseases.

Granzyme B inhibition reduces disease severity in autoimmune blistering diseases

Pemphigoid diseases refer to a group of severe autoimmune skin blistering diseases characterized by subepidermal blistering and loss of dermal-epidermal adhesion induced by autoantibody and immune cell infiltrate at the dermal-epidermal junction and upper dermis. Here, we explore the role of the immune cell-secreted serine protease, granzyme B, in pemphigoid disease pathogenesis using three independent murine models. In all models, granzyme B knockout or topical pharmacological inhibition significantly reduces total blistering area compared to controls. In vivo and in vitro studies show that granzyme B contributes to blistering by degrading key anchoring proteins in the dermal-epidermal junction that are necessary for dermal-epidermal adhesion. Further, granzyme B mediates IL-8/macrophage inflammatory protein-2 secretion, lesional neutrophil infiltration, and lesional neutrophil elastase activity. Clinically, granzyme B is elevated and abundant in human pemphigoid disease blister fluids and lesional skin. Collectively, granzyme B is a potential therapeutic target in pemphigoid diseases.

Type XVII collagen interacts with the aPKC-PAR complex and maintains epidermal cell polarity

Type XVII collagen (COL17) is a transmembrane protein expressed in the basal epidermis. COL17 serves as a niche for epidermal stem cells, and although its reduction has been implicated in altering cell polarity and ageing of the epidermis, it is unknown how COL17 affects epidermal cell polarity. Here, we uncovered COL17 as a binding partner of the aPKC-PAR complex, which is a key regulating factor of cell polarity. Immunoprecipitation-immunoblot assay and protein-protein binding assay revealed that COL17 interacts with aPKC and PAR3. COL17 deficiency or epidermis-specific aPKCλ deletion destabilized PAR3 distribution in the epidermis, while aPKCζ knockout did not. Asymmetrical cell division was pronounced in COL17-null neonatal paw epidermis. These results show that COL17 is pivotal for maintaining epidermal cell polarity. Our study highlights the previously unrecognized role of COL17 in the basal keratinocytes.

Collagen XVII Processing and Blistering Skin Diseases

Collagen XVII (COL17) is a hemidesmosomal transmembrane protein in the skin, which, in several autoimmune blistering skin diseases, may be targeted by autoantibodies. In addition, loss-of-function mutations in the COL17A1 gene induce a subtype of junctional epidermolysis bullosa. The extracellular domain of COL17 can be physiologically cleaved from the cell surface by ADAM family proteins in a process known as ectodomain shedding. COL17 ectodomain shedding is thought to be associated with the migration and proliferation of keratinocytes. Furthermore, the C-terminal cleavage of COL17 may be associated with basement membrane formation. COL17 can be targeted by various proteases, including MMP9, neutrophil elastase, plasmin and granzyme B, which may be associated with blister formation in pemphigoid diseases. Interestingly, cleavage of COL17 may induce neoepitopes on the proteolysed fragments, and such induction is associated with dynamic structural changes. This review summarizes the current understanding of cleavage of COL17, and how such cleavage relates to blistering skin diseases.

Japanese guidelines for the management of pemphigoid (including epidermolysis bullosa acquisita)

The pemphigoid group is a category of autoimmune subepidermal blistering diseases in which autoantibodies deposit linearly at the epidermal basement membrane zone (BMZ). The main subtypes of pemphigoid mediated by immunoglobulin G autoantibodies are bullous pemphigoid (BP), mucous membrane pemphigoid (MMP) and epidermolysis bullosa acquisita (EBA). To establish the first guidelines approved by the Japanese Dermatological Association for the management of pemphigoid diseases, the Committee for Guidelines for the Management of Pemphigoid Diseases (Including EBA) was founded as part of the Study Group for Rare Intractable Skin Diseases under the Ministry of Health, Labor and Welfare Research Project on Overcoming Intractable Diseases. These guidelines aim to provide current information for the management of BP, MMP and EBA in Japan. Based on evidence, the guidelines summarize the clinical and immunological manifestations, pathophysiologies, diagnostic criteria, disease severity determination criteria, treatment algorithms and treatment recommendations. Because of the rarity of these diseases, there are few clinical studies with a high degree of evidence, so several parts of these guidelines were established based on the opinions of the Committee. To further optimize these guidelines, periodic revision in line with the new evidence is necessary.

Life before and beyond blistering: The role of collagen XVII in epidermal physiology

Type XVII collagen (COL17) is a transmembranous protein that is mainly expressed in the epidermal basal keratinocytes. Epidermal-dermal attachment requires COL17 expression at the hemidesmosomes of the epidermal basement membrane zone because congenital COL17 deficiency leads to junctional epidermolysis bullosa and acquired autoimmunity to COL17 induces bullous pemphigoid. Recently, in addition to facilitating epidermal-dermal attachment, COL17 has been reported to serve as a niche for hair follicle stem cells, to regulate proliferation in the interfollicular epidermis and to be present along the non-hemidesmosomal plasma membrane of epidermal basal keratinocytes. This review focuses on the physiological properties of COL17 in the epidermis, its role in maintaining stem cells and its association with signalling pathways. We propose possible solutions to unanswered questions in this field.

A Cross-Sectional Study Comparing the Prevalence of Bullous Pemphigoid Autoantibodies in 275 Cases of Type II Diabetes Mellitus Treated With or Without Dipeptidyl Peptidase-IV Inhibitors

Background: Anti-hyperglycemic drug dipeptidyl peptidase-IV inhibitors (DPP-4i) have recently been recognized as bullous pemphigoid (BP) inducing drugs. It remains uncertain whether DPP-4i induce BP-IgG autoantibodies before the onset of BP. Objective: To evaluate the effect of DPP-4i in the development of BP-IgG autoantibodies in type 2 diabetes mellitus (T2DM) patients. Methods: A cross-sectional study on 221 DPP-4i (+) and 54 DPP-4i (-) T2DM cases was conducted. BP180 NC16A, BP230, and full-length BP180 ELISAs were used to detect the BP-IgG autoantibodies. We have also statistically analyzed the proportion of age, gender, intake periods of DPP-4i, and hemoglobin A1c level between anti-full-length BP180 IgG-positive and -negative DPP-4i (+) T2DM cases to identify co-founding factors. Results: BP180 NC16A ELISA, BP230 ELISA, and full-length BP180 ELISA were positive in 1.8, 2.2, and 10.9% of DPP-4i (+) T2DM cases, respectively; in contrast, they were positive in 0, 7.4, and 5.6% of DPP-4i (-) T2DM cases, respectively. The odds ratio for the development of BP-IgG autoantibodies detected by full-length BP180 ELISA was 2.070 for DPP-4i (+). There were no significant differences between the genders, intake periods of DPP-4i, nor of hemoglobin A1c levels, the anti-full-length BP180 IgG-positive cases tended to be significantly older than anti-full-length BP180 IgG-negative cases (median 74 vs. 69, p = 0.025) in the DPP-4i (+) T2DM cases. Limitations: We focused the analysis on DPP-4i intake and not on the effects of metformin and other drugs. Conclusion: Exposure to specific DPP-4i may induce the development of anti-full-length BP180 autoantibodies even in T2DM patients without any clinical symptoms of BP. Aging would be a risk factor to develop anti-full-length BP180-IgG autoantibody in DPP-4i (+) T2DM cases.

Immune Reaction to Type XVII Collagen Induces Intramolecular and Intermolecular Epitope Spreading in Experimental Bullous Pemphigoid Models

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is induced by autoantibodies to type XVII collagen (COL17). Previous studies demonstrated that COL17 harbors several epitopes targeted by autoreactive T and B cells and that the target epitopes change sequentially during the disease course. To elucidate the details of the humoral immune response to COL17, we used an active BP mouse model in which BP is induced by the adoptive transfer of spleen cells from wild-type mice immunized with human COL17-expressing skin grafting to immunodeficient COL17-humanized (Rag-2-/-, mouse Col17-/-, human COL17+) mice. By immunoblot analysis, antibodies to the NC16A domain and other extracellular domains (ECDs) of COL17 were detected earlier than antibodies to intracellular domains (ICDs) in the active BP model. Time course analysis by enzyme-linked immunosorbent assay demonstrated a delayed peak of antibodies to ICD epitopes in active BP model. The blockade of CD40-CD40 ligand interaction soon after the adoptive transfer suppressed the production of antibodies to the non-collagenous 16A (NC16A) domain but not to an ICD epitope, suggesting the sequential activation from T and B cells against the ECD epitopes including the NC16A domain to those against ICD epitopes in vivo. Both wild-type mice immunized with a fragment of the NC16A domain and the recipients of those spleen cells produced IgG antibodies to ICD and ECD epitopes, showing intramolecular epitope spreading from the NC16A domain to other epitopes of COL17. Furthermore, we found that a portion of the active BP model mice show intermolecular epitope spreading from human COL17 to murine BP230. The appearance of antibodies to ICD epitopes of COL17 or of antibodies to murine BP230 did not correlate with the skin changes in the mice, suggesting that those antibodies have low pathogenicity. These results suggest that the immune response to the ECD epitopes of COL17, especially to the NC16A domain, triggers intramolecular, and intermolecular epitope spreading to ICD epitopes of COL17 and to murine BP230. These novel findings provide insight into the mechanism of epitope spreading in organ-specific, antibody-mediated autoimmune disorders.

Dipeptidyl Peptidase-4 Inhibitor-Associated Bullous Pemphigoid

Bullous pemphigoid (BP) is an organ-specific autoantibody-mediated blistering skin disease that mainly affects the elderly. Typical clinical features include the widespread blisters, often preceded by and/or associated with itchy urticarial or eczema-like lesions. BP patients have circulating autoantibodies against BP180 and/or the plakin family protein BP230 both of which are components of hemidesmosomes in basal keratinocytes. Most BP autoantibodies particularly target the epitopes within the non-collagenous NC16A domain of BP180. Clinical findings and murine models of BP have provided evidence of a pathogenic role of anti-NC16A autoantibodies. However, it is largely unknown what triggers the breakage of immunotolerance against BP180 in elderly individuals. The incidence of BP has been increased over the past two decades in several countries. Aside from aging populations, the factors behind this phenomenon are still not fully understood. Neurodegenerative diseases such as multiple sclerosis, Parkinson's disease, and certain dementias are independent risk factors for BP. Recently several case reports have described BP in patients with diabetes mellitus (DM) patients who have been treated with dipeptidyl peptidase-4 inhibitors (DPP-4i or gliptins), which are a widely used class of anti-DM drugs. The association between the use of DPP-4is, particularly vildagliptin, and BP risk has been confirmed by several epidemiological studies. Evidence suggests that cases of gliptin-associated BP in Japan display certain features that set them apart from cases of “regular” BP. These include a “non-inflammatory” phenotype, targeting by antibodies of different immunodominant BP180 epitopes, and a specific association with the human leukocyte antigen (HLA) types. However, recent studies in European populations have found no major differences between the clinical and immunological characteristics of gliptin-associated BP and “regular” BP. The DPP-4 protein (also known as CD26) is ubiquitously expressed and has multiple functions in various cell types. The different effects of the inhibition of DPP-4/CD26 activity include, for example, tissue modeling and regulation of inflammatory cells such as T lymphocytes. Although the pathomechanism of gliptin-associated BP is currently largely unknown, investigation of the unique effect of gliptins in the induction of BP may provide a novel route to better understanding of how immunotolerance against BP180 breaks down in BP.

Preferential Reactivity of Dipeptidyl Peptidase-IV Inhibitor-Associated Bullous Pemphigoid Autoantibodies to the Processed Extracellular Domains of BP180

Bullous pemphigoid (BP) is a common autoimmune blistering disease in which autoantibodies target the hemidesmosomal components BP180 and/or BP230 in basal keratinocytes. In BP, 80 to 90% of autoantibodies target the juxtamembranous extracellular non-collagenous 16th A (NC16A) domain of BP180. Recently, the administration of dipeptidyl peptidase-IV inhibitors (DPP4i), which are widely used as antihyperglycemic drugs, has been recognized to be a causative factor for BP. DPP4i-associated BP (DPP4i-BP) autoantibodies tend to target epitopes on non-NC16A regions of BP180, and the pathomechanism for the development of the unique autoantibodies remains unknown. To address the characteristics of DPP4i-BP autoantibodies in detail, we performed epitope analysis of 18 DPP4i-BP autoantibodies targeting the non-NC16A domains of BP180 using various domain-specific as well as plasmin-digested polypeptides derived from recombinant BP180. Firstly, Western blotting showed that only one DPP4i-BP serum reacted with the epitopes on the intracellular domain of BP180, and no sera reacted with the C-terminal domain of the molecule. In addition, only 2 DPP4i-BP sera reacted with BP230 as determined by enzyme-linked immunosorbent assay. Thus, DPP4i-BP autoantibodies were found to mainly target the non-NC16A mid-portion of the extracellular domain of BP. Interestingly, Western blotting using plasmin-digested BP180 as a substrate revealed that all of the DPP4i-BP sera reacted more intensively with the 97-kDa processed extracellular domain of BP180, which is known as the LABD97 autoantigen, than full-length BP180 did. All of the DPP4i-BP autoantibodies targeting the LABD97 autoantigen were IgG1, and IgG4 was observed to react with the molecule in only 7 cases (38.9%). In summary, the present study suggests that IgG1-class autoantibodies targeting epitopes on the processed extracellular domain of BP180, i.e., LABD97, are the major autoantibodies in DPP4i-BP.

Dipeptidyl peptidase IV inhibitor-associated bullous pemphigoid: a recently recognized autoimmune blistering disease with unique clinical, immunological and genetic characteristics

Bullous pemphigoid (BP) is an organ-specific autoantibody-mediated autoimmune blistering skin disorder that tends to affect the elderly. Tense blister formation associated with itchy urticarial erythema is clinically observed in BP, and subepidermal blister formation with eosinophilic infiltration is a histopathological characteristic. BP autoantibodies target two hemidesmosomal components in basal keratinocytes: BP180 and BP230. Anti-BP180 autoantibodies play major roles in blister formation. Although the autoantibody-mediated pathomechanism of blister formation has been extensively studied, little is known about how and why immune tolerance to BP180 may be broken in certain elderly individuals. Recently, BP has been increasingly reported in diabetes mellites (DM) patients receiving dipeptidyl peptidase-IV inhibitors (DPP4is), which are widely used anti-DM drugs. Pharmacovigilance and cohort studies have revealed that DPP4is, especially vildagliptin, teneligliptin, and linagliptin, are a potential risk factor for BP onset. Interestingly, it has been revealed that Japanese DPP4i-BP tends to show a non-inflammatory phenotype, with less erythema than normal BP, and that DPP4i-BP autoantibodies target distinct epitopes on BP180. In addition, human leukocyte antigen-DQB1*03:01 was identified as the major haplotype in Japanese DPP4i-BP. This review summarizes the latest understanding of the pathogenesis of BP, with a special focus on the recently recognized DPP4i-BP.

Fc-binding proteins enhance autoantibody-induced BP180 depletion in pemphigoid

Immunoglobulins (Igs) consist of two antigen-binding regions (Fab) and one constant region (Fc). Protein A and protein G are bacterial proteins used for the purification of IgG by virtue of their high affinities for the Fc fragment. Rheumatoid factors are autoantibodies against IgG Fc fragments, which are present in the body under physiological conditions. Little is known about the influence of Fc-binding proteins on the pathogenicity of antibody-induced autoimmune diseases. Pemphigoid diseases are a group of autoimmune subepidermal blistering disorders that includes bullous pemphigoid and mucous membrane pemphigoid. IgGs targeting the non-collagenous NC16A domain of the 180-kDa bullous pemphigoid antigen (BP180) are known to induce skin fragility in mice and the depletion of BP180 in keratinocytes. In this study, mAb against NC16A in combination with Fc-binding proteins was found to enhance BP180 depletion. Although mAb against the C-terminus of BP180 does not show pathogenicity in vivo or in vitro, mAb treatment with Fc-binding proteins clearly induced skin fragility in mice and BP180 depletion in keratinocytes. Anti-BP180 mAbs and Fc-binding proteins were colocalized in the cytoplasm and at the basement membrane zone. Cell adhesion strengths were decreased in parallel with BP180 amounts. Clinically, bullous pemphigoid patients had higher rheumatoid factor titers than controls. Anti-BP180 mAb in combination with high-titer rheumatoid factor serum was found to enhance BP180 depletion. Furthermore, saliva from mucous membrane pemphigoid patients contained larger quantities of bacteria and Fc-binding proteins than controls. Our results suggest that Fc-binding proteins (rheumatoid factor or protein G) may enhance the pathogenicity of autoantibodies in pemphigoid diseases. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Dipeptidyl peptidase-4 inhibitors-associated bullous pemphigoid: A retrospective study of 168 pemphigoid and 9,304 diabetes mellitus patients

AIMS/INTRODUCTION

Bullous pemphigoid (BP) might be drug-induced. The present study evaluated the relationship between BP and dipeptidyl peptidase-4 inhibitors (DPP4Is).

MATERIALS AND METHODS

We recruited patients diagnosed with BP at Ogaki Municipal Hospital from 1 December 2009 through 31 December 2017. We retrospectively collected data from medical records and divided patients into two groups based on whether they received DPP4Is. Additionally, we determined the incidence of BP in patients who were first prescribed DPP4Is at our hospital during the study period.

RESULTS

Of 168 patients diagnosed with BP, 133 (79.1%) were positive for anti-BP180NC16a antibody. A total of 32 (19.0%) patients had been prescribed a DPP4I, 21 of whom (65.6%) were positive for anti-BP180NC16a antibody; this rate was lower than that in patients not receiving a DPP4I (82.3%; P = 0.0360). A total of 16 patients with type 2 diabetes mellitus had not been prescribed a DPP4I; only one (6.3%) was positive for anti-BP180NC16a antibody (P = 0.0339). During the study period, 9,304 patients were prescribed DPP4Is, eight of whom developed BP; six (75.0%) had non-inflammatory BP, and five of the six (83.3%) were negative for anti-BP180NC16a antibody.

CONCLUSIONS

The positive rate of anti-BP180NC16a antibody was lower in BP patients with DPP4I than without DPP4I, regardless of type 2 diabetes mellitus. The antibody titer was low in both the overall and type 2 diabetes mellitus populations. The prevalence of BP in 9,304 patients receiving DPP4Is was 0.0859%, which is higher than that in the general population. As DPP4Is are common diabetes treatments, we must be aware of the risk of BP.

Somatic recombination underlies frequent revertant mosaicism in loricrin keratoderma

We demonstrate that revertant mosaicism frequently occurs in loricrin keratoderma and that somatic recombination is the major mechanism underlying this therapeutically important phenomenon.

Revertant mosaicism is a phenomenon in which pathogenic mutations are rescued by somatic events, representing a form of natural gene therapy. Here, we report on the first evidence for revertant mosaicism in loricrin keratoderma (LK), an autosomal dominant form of ichthyosis caused by mutations in LOR on 1q21.3. We identified two unrelated LK families exhibiting dozens of previously unreported white spots, which increased in both number and size with age. Biopsies of these spots revealed that they had normal histology and that causal LOR mutations were lost. Notably, dense single nucleotide polymorphism mapping identified independent copy-neutral loss-of-heterozygosity events on chromosome 1q extending from regions centromeric to LOR to the telomere in all investigated spots, suggesting that somatic recombination represents a common reversion mechanism in LK. Furthermore, we demonstrated that reversion of LOR mutations confers a growth advantage to cells in vitro, but the clinically limited size of revertant spots suggests the existence of mechanisms constraining revertant clone expansion. Nevertheless, the identification of revertant mosaicism in LK might pave the way for revertant therapy for this intractable disease.

BP180 Autoantibodies Target Different Epitopes in Multiple Sclerosis or Alzheimer's Disease than in Bullous Pemphigoid

Neurologic patients have an increased risk for bullous pemphigoid (BP), in which autoantibodies target BP180, a cutaneous basement membrane protein also expressed in the brain. Here we show that 53.6% of sera from patients with multiple sclerosis (MS) (n = 56) had IgG reactivity against full-length BP180 in immunoblotting, while in BP180 non-collagenous 16A ELISA (n = 143), only 7.7% of MS samples studied were positive. Epitope mapping with 13 fusion proteins covering the entire BP180 polypeptide revealed that in MS and Alzheimer's disease (AD) patients, IgG autoantibodies target regions located in the intracellular and mid-extracellular parts of BP180, but not the well-known BP epitopes located in the non-collagenous 16A domain and the distal part of extracellular domain. In indirect immunofluorescence analysis, 8.1% of MS sera recognized the cutaneous basement membrane and in full-length BP180 ELISA analysis, 7.5% MS and AD sera were positive, indicating that these autoantibodies rarely recognize BP180 in its native conformation. Thus, in MS and AD patients, BP180 autoantibodies have a different epitope profile than in patients with BP, and seldom bind to native BP180. This explains the inability of these autoantibodies to cause skin symptoms. Our results suggest that the autoantibodies against BP180 alone are not sufficient to induce BP in MS and AD patients.

The direct binding of collagen XVII and collagen IV is disrupted by pemphigoid autoantibodies

The basement membrane zone (BMZ) is framed by hemidesmosomes and extracellular matrix (ECM) including collagen IV (COL4). Hemidesmosomes are multiprotein complexes that include collagen XVII (COL17). BMZ proteins can be targeted in autoimmune subepidermal blistering diseases, e.g., pemphigoid targeting COL17. The blistering mechanisms in pemphigoid have not been fully elucidated, especially in mucous membrane pemphigoid (MMP), which mainly affects the mucosa. In this study, we showed that oral lesions in pemphigoid may be attributed to the inhibition of protein-protein interactions by autoantibodies. Using immunoprecipitation, we revealed that COL17 directly binds to COL4 in normal human keratinocytes and normal human oral keratinocytes. In particular, the C-terminus of COL17 is binding site to COL4 in oral keratinocytes. The precise COL4-binding region on COL17 was determined by protein-protein binding assay to be from amino acid Gly1175 to Asp1340 on the C-terminus. MMP-IgG or mAb recognizing the C-terminus hindered the interaction of COL17 with COL4 in oral keratinocytes. Furthermore, keratinocyte adhesion strength to COL4-coated plates was significantly reduced by the treatment of mAb against the C-terminus. In addition, the inflammatory infiltrates around perilesions were significantly less in MMP compared to BP. These results indicate that pemphigoid IgG targeting the C-terminus plays a pathogenic role in blister formation in the oral mucosa to inhibit protein interactions with less inflammation.

Rituximab therapy for refractory autoimmune bullous diseases: A multicenter, open-label, single-arm, phase 1/2 study on 10 Japanese patients

This was a multicenter study of rituximab, a chimeric monoclonal immunoglobulin G antibody directed against CD20, for the treatment of refractory autoimmune bullous diseases (pemphigus and pemphigoid). Ten patients (three with pemphigus vulgaris, six with pemphigus foliaceus and one with bullous pemphigoid) were treated with a single cycle of rituximab (four weekly infusions at a dose of 375 mg/m² of body surface area). The primary end-points were the number of serious adverse events and rate of complete remission at 40 weeks. Five patients (50%) achieved complete remission with minimal therapy (defined as no active lesions with lower doses of systemic corticosteroids compared to that with prednisolone 10 mg/day). Improvements in clinical scores (Pemphigus Disease Area Index) and decreases in autoantibody titers in the sera were observed in the four pemphigus patients who failed to achieve complete remission. This suggests that rituximab was effective in nine of 10 cases. Two serious adverse events (Pneumocystis carinii pneumonia and septic shock due to infectious arthritis) were observed and adequately treated with hospitalization. CD19-positive B lymphocytes in the peripheral blood decreased on day 29 following rituximab treatment, and remained at low levels throughout the observation period (280 days). Our results confirmed the efficacy of rituximab therapy for refractory autoimmune bullous diseases in Japan.