Humanization of autoantigen

Collagen XVII

Collagen XVII has been identified as having a role in inherited junctional epidermolysis bullosa non-Herlitz (JEB-other, MIM #226650). The role of collagen XVII in both autoimmune and genetic blistering disorders demonstrates its relevance to dermal-epidermal adhesion. Collagen XVII is a major structural component of the hemidesmosome (HD), a highly specialized multiprotein complex that mediates the anchorage of basal epithelial cells to the underlying basement membrane in stratified, pseudostratified, and transitional epithelia. This article examines the genetic and pathological features of collagen XVII.

Blockade of autoantibody-initiated tissue damage by using recombinant fab antibody fragments against pathogenic autoantigen

Activation of the complement cascade via the classical pathway is required for the development of tissue injury in many autoantibody-mediated diseases. It therefore makes sense to block the pathological action of autoantibodies by preventing complement activation through inhibition of autoantibody binding to the corresponding pathogenic autoantigen using targeted Fab antibody fragments. To achieve this, we use bullous pemphigoid (BP) as an example of a typical autoimmune disease. Recombinant Fabs against the non-collagenous 16th-A domain of type XVII collagen, the main pathogenic epitope for autoantibodies in BP, were generated from antibody repertoires of BP patients by phage display. Two Fabs, Fab-B4 and Fab-19, showed marked ability to inhibit the binding of BP autoantibodies and subsequent complement activation in vitro. In the in vivo experiments using type XVII collagen humanized BP model mice, these Fabs protected mice against BP autoantibody-induced blistering disease. Thus, the blocking of pathogenic epitopes using engineered Fabs appears to demonstrate efficacy and may lead to disease-specific treatments for antibody-mediated autoimmune diseases.

[Novel animal models for bullous pemphigoid utilized by "humanization of autoantigen"]

Animal models of human diseases are very useful to better understand their pathomechanism and to develop new therapies. However, due to the differences among different species, it is sometimes difficult to reproduce reliable diseases phenotype in animals. Bullous pemphigoid is the most common autoimmune blistering skin disease, in which circulating IgG autoantibodies directed against type XVII collagen (COL17) leads to skin blister formation. Interestingly, due to significant interspecies differences in its amino acid sequences in major pathogenic epitope on COL17, passive transfer of auto-antibodies (Abs) from patients with bullous pemphigoid into mice failed to induce blister formation. To overcome this species' differences, we have recently established a novel molecular method "humanization of autoantigen" by genetic manipulation. Using COL17-humanized mice, we have established 2 different mouse models of bullous pemphigoid. One is by injecting human auto-Abs from bullous pemphigoid patients into the neonatal COL17-humanized mice. Another model was induced by mouse Abs to human COL17 passively transferred from mother via placenta and milk into the neonatal COL17-humanized mice. "Humanization of autoantigen" is a novel and potential method to produce animal models for autoimmune diseases.

Keratinocyte-/fibroblast-targeted rescue of Col7a1-disrupted mice and generation of an exact dystrophic epidermolysis bullosa model using a human COL7A1 mutation

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe hereditary bullous disease caused by mutations in COL7A1, which encodes type VII collagen (COL7). Col7a1 knockout mice (COL7(m-/-)) exhibit a severe RDEB phenotype and die within a few days after birth. Toward developing novel approaches for treating patients with RDEB, we attempted to rescue COL7(m-/-) mice by introducing human COL7A1 cDNA. We first generated transgenic mice that express human COL7A1 cDNA specifically in either epidermal keratinocytes or dermal fibroblasts. We then performed transgenic rescue experiments by crossing these transgenic mice with COL7(m+/-) heterozygous mice. Surprisingly, human COL7 expressed by keratinocytes or by fibroblasts was able to rescue all of the abnormal phenotypic manifestations of the COL7(m-/-) mice, indicating that fibroblasts as well as keratinocytes are potential targets for RDEB gene therapy. Furthermore, we generated transgenic mice with a premature termination codon expressing truncated COL7 protein and performed the same rescue experiments. Notably, the COL7(m-/-) mice rescued with the human COL7A1 allele were able to survive despite demonstrating clinical manifestations very similar to those of human RDEB, indicating that we were able to generate surviving animal models of RDEB with a mutated human COL7A1 gene. This model has great potential for future research into the pathomechanisms of dystrophic epidermolysis bullosa and the development of gene therapies for patients with dystrophic epidermolysis bullosa.

A novel humanized neonatal autoimmune blistering skin disease model induced by maternally transferred antibodies

All mammal neonates receive maternal Abs for protection against pathogenic organisms in the postnatal environment. However, neonates can experience serious adverse reactions if the Abs transferred from the mother recognize self-molecules as autoAgs. In this study, we describe a novel model for autoimmune disease induced by transferred maternal Abs in genetically transformed Ag-humanized mice progeny. Bullous pemphigoid is the most common life-threatening autoimmune blistering skin disease that affects the elderly, in which circulating IgG autoAbs are directed against epidermal type XVII collagen (COL17). We have established a genetically manipulated experimental mouse model in which maternal Abs against human COL17 are transferred to pups whose skin expresses only human and not mouse COL17, resulting in blistering similar to that seen in patients with bullous pemphigoid. Maternal transfer of pathogenic Abs to humanized neonatal mice is a unique and potential experimental system to establish a novel autoimmune disease model.

Basement membranes and human disease

In 1990, the role of basement membranes in human disease was established by the identification of COL4A5 mutations in Alport's syndrome. Since then, the number of diseases caused by mutations in basement membrane components has steadily increased as has our understanding of the roles of basement membranes in organ development and function. However, many questions remain as to the molecular and cellular consequences of these mutations and the way in which they lead to the observed disease phenotypes. Despite this, exciting progress has recently been made with potential treatment options for some of these so far incurable diseases.

Collagen XVII participates in keratinocyte adhesion to collagen IV, and in p38MAPK-dependent migration and cell signaling

Collagen XVII (COL17) participates in keratinocyte adhesion and possibly migration, as COL17 defects disrupt keratinocyte-basal lamina adhesion and underlie the disease non-Herlitz junctional epidermolysis bullosa. Using small interference RNA (siRNA) to knock down COL17 expression in HaCaT cells, we assessed cell characteristics, including adhesion, migration, and signaling. Control and siRNA-transfected keratinocytes showed no difference in adhesion on plastic dishes after incubation for 8 hours in serum-free keratinocyte-growth medium; however, when grown on collagen IV alone or BD matrigel (containing collagen IV and laminin isoforms), COL17-deficient cells showed significantly reduced adhesion compared with controls (P<0.01), and mitogen-activated protein kinase (MAPK)/ERK kinase (MEK)1/2 and MAPK showed reduced phosphorylation. Furthermore, COL17-deficient HaCaT cells plated on plastic exhibited reduced motility that was p38MAPK-dependent (after addition of the p38MAPK inhibitor SB203580). Together, these results suggest that COL17 has significantly wider signaling roles than were previously thought, including the involvement of COL17 in keratinocyte adhesion to collagen IV, in p38MAPK-dependent cell migration, and multiple cell signaling events pertaining to MEK1/2 phosphorylation.

IgG autoantibody reactivity against bullous pemphigoid (BP) 180 and BP230 in elderly patients with pruritic dermatoses

BACKGROUND

Pruritic dermatoses of the elderly often pose a diagnostic and therapeutic challenge. Specifically, a prodromal phase of bullous pemphigoid (BP) has to be considered in patients with pruritic lesions of polymorphic appearance. These conditions frequently do not fulfil all the clinical, histological and immunopathological criteria for establishing the diagnosis of BP.

OBJECTIVES

To investigate IgG reactivity against the autoantigens of BP, BP180 and BP230, by enzyme-linked immunosorbent assay, in elderly patients affected with various pruritic disorders who had never experienced clinically apparent blisters.

METHODS

The sera of 15 elderly patients with pruritic disorders (group I) were tested for IgG reactivity against BP180 and BP230. Also included were 30 patients with full-blown BP (group II) and 25 age-matched patients with immediate-type allergic reactions (group III).

RESULTS

Thirty-three per cent of the patients with pruritic disorders (group I) showed IgG against BP230 and/or BP180: four of 15 patients had IgG against BP230 while two of the 15 group I patients were BP180 reactive. All the BP sera (group II) showed IgG reactivity against BP180 and/or BP230. Notably, two of 25 control sera (group III) showed IgG reactivity against either BP180 or BP230.

CONCLUSIONS

The present findings suggest that IgG reactivity against BP230 (i.e. the COOH terminus), and to a lesser extent against BP180, is a common finding in pruritic disorders of the elderly with a wide clinical spectrum. IgG-mediated autoimmunity against the intracellular BP230 may facilitate a chronic, inflammatory response eventually leading to full-blown BP which is presumably associated with IgG against BP180.

A novel ELISA reveals high frequencies of BP180-specific IgE production in bullous pemphigoid

Bullous pemphigoid (BP) is a humoral autoimmune disease directed predominantly against the non-collagenous NC16A domain of the BP180 hemidesmosomal protein. Our laboratory has recently shown, using a mouse xenograft model, that passive transfer of IgE autoantibodies from BP sera induces a skin phenotype that recapitulates the early phases of the disease. Herein, we describe the development of a highly specific and sensitive ELISA to detect circulating IgE autoantibodies that recognize BP180-NC16A. Using this assay, we detected NC16A-specific IgE-class autoantibodies in 77% of BP sera. This frequency, which is significantly higher than reported previously, is comparable to that of anti-NC16A IgG autoantibody production. In 3 BP patients monitored over time, the circulating NC16A-specific levels of both IgE and IgG were associated with clinical disease activity; however, patient sera did not always contain high levels of both isotypes. In conclusion, our ELISA provides a highly sensitive and specific tool for the detection of BP180-specific IgE in patient sera. Furthermore, we report that the majority of BP sera contain both IgE and IgG class autoantibodies specific for NC16A and suggest that screening for both isotypes of autoantibodies may provide a better diagnostic value than IgG alone.

Bullous pemphigoid: a prototypical antibody-mediated organ-specific autoimmune disease

Bullous pemphigoid (BP) is a prototypical organ-specific autoimmune disease. Autoantibodies unfold their blister-inducing potential by triggering an Fcgamma-dependent inflammatory reaction. The study by Iwata et al. in this issue provides the first direct evidence that IgG autoantibodies from BP patients may also weaken cell-matrix adhesion by depleting BP180/type XVII collagen from cultured keratinocytes. These novel findings shed new light on additional mechanisms of blister formation in pemphigoid diseases and open the way for further informative studies.

Diagnosis and clinical severity markers of bullous pemphigoid

The use of a broad spectrum of novel detection systems for autoantibodies to the basement membrane proteins BP180 and BP230 has greatly facilitated the diagnosis of bullous pemphigoid, which most likely explains its increasing incidence in central Europe. Because the pathogenic relevance of antibodies to human BP180 has been convincingly shown both in vitro and in vivo, repeated testing for these antibodies appears to be helpful in guiding treatment decisions during the course of the disease.

Type XVII collagen is a key player in tooth enamel formation

Inherited tooth enamel hypoplasia occurs due to mutations in genes that encode major enamel components. Enamel hypoplasia also has been reported in junctional epidermolysis bullosa, caused by mutations in the genes that encode type XVII collagen (COL17), a component of the epithelial-mesenchymal junction. To elucidate the pathological mechanisms of the enamel hypoplasia that arise from the deficiency of epithelial-mesenchymal junction molecules, such as COL17, we investigated tooth formation in our recently established Col17(-/-) and Col17 rescued mice. Compared with wild-type mice, the incisors of the Col17(-/-) mice exhibited reduced yellow pigmentation, diminished iron deposition, delayed calcification, and markedly irregular enamel prisms, indicating the presence of enamel hypoplasia. The molars of the Col17(-/-) mice demonstrated advanced occlusal wear. These abnormalities were corrected in the Col17 rescued humanized mice. Thus, the Col17(-/-) mice clearly reproduced the enamel hypoplasia in human patients with junctional epidermolysis bullosa. We were able to investigate tooth formation in the Col17(-/-) mice because the Col17(-/-) genotype is not lethal. Col17(-/-) mouse incisors had poorly differentiated ameloblasts that lacked enamel protein-secreting Tomes' processes and reduced mRNA expression of amelogenin, ameloblastin, and of other enamel genes. These findings indicated that COL17 regulates ameloblast differentiation and is essential for normal formation of Tomes' processes. In conclusion, COL17 deficiency disrupts the epithelial-mesenchymal interactions, leading to both defective ameloblast differentiation and enamel malformation.

Subepidermal blistering induced by human autoantibodies to BP180 requires innate immune players in a humanized bullous pemphigoid mouse model

Bullous pemphigoid (BP) is a cutaneous autoimmune inflammatory disease associated with subepidermal blistering and autoantibodies against BP180, a transmembrane collagen and major component of the hemidesmosome. Numerous inflammatory cells infiltrate the upper dermis in BP. IgG autoantibodies in BP fix complement and target multiple BP180 epitopes that are highly clustered within a non-collagen linker domain, termed NC16A. Anti-BP180 antibodies induce BP in mice. In this study, we generated a humanized mouse strain, in which the murine BP180NC14A is replaced with the homologous human BP180NC16A epitope cluster region. We show that the humanized NC16A (NC16A+/+) mice injected with anti-BP180NC16A autoantibodies develop BP-like subepidermal blisters. The F(ab')(2) fragments of pathogenic IgG fail to activate the complement cascade and are no longer pathogenic. The NC16A+/+ mice pretreated with mast cell activation blocker or depleted of complement or neutrophils become resistant to BP. These findings suggest that the humoral response in BP critically depends on innate immune system players.

Multicenter prospective study of the humoral autoimmune response in bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune bullous disease, associated with autoantibodies directed against the hemidesmosomal components BP180 and BP230. In this study for the first time different laboratories have analyzed the autoantibody profile in the same group of 49 prospectively recruited BP patients. The results show that: 1) disease severity and activity correlated with levels of IgG against the BP180-NC16A domain, but also against a COOH-terminal epitope of BP180, 2) distinct epitopes of the BP180 ectodomain other than BP180-NC16A were recognized by 96% of the BP sera; and 3) the combined use of BP180 and BP230 ELISA led to the detection of IgG autoantibodies in all the BP sera. These results demonstrate the usefulness of the combined ELISAs based on various BP180 and BP230 fragments in establishing the diagnosis of BP and support the concept that BP180 is the major autoantigen of BP.

Genetically engineered mouse models for skin research: taking the next step

Genetically engineered mouse models are invaluable to investigators in nearly all areas of biomedical research. The use of genetically engineered mice has allowed researchers to explore fundamental functions of genes in a mammal that shares substantial similarities with human physiology and pathology. Genetically engineered mice are often used as animal models of human diseases that are vital tools in investigating disease development and in developing and testing novel therapies. Gene targeting in embryonic stem cells allows endogenous genes to be specifically altered. As knowledge regarding precise genetic abnormalities underlying a variety of dermatological conditions continues to emerge, the ability to introduce corresponding alterations in endogenous gene loci in mice, often at a single base pair level, has become essential for detailed studies of these genetic diseases. In this review, we provide examples of mouse models harboring modified endogenous gene(s), generated using the technique commonly referred to as the "knock-in" approach, to exemplify the important and sometimes superior role of this methodology in dermatological research.

Serum levels of IgE anti-BP180 and anti-BP230 autoantibodies in patients with bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is a subepidermal blistering disease characterized by autoantibodies against the hemidesmosomal proteins, BP180 and BP230. NC16A, a non-collagenous stretch of the BP180 ectodomain is the primary target of pathogenic IgG antibodies. Whereas IgG anti-BP180 autoantibodies play a primary role in the pathogenesis, there is a growing number of data regarding the potential pathogenic roles of IgE class autoantibodies in BP.

OBJECTIVES

To examine the levels of IgG and IgE autoantibodies against BP180 and BP230, and to investigate mutual association and clinical relevance.

METHODS

Sera obtained from 67BP patients and 36 healthy donors were subjected to ELISA assays to measure serum IgG and IgE levels of anti-BP180 and anti-BP230 antibodies.

RESULTS

IgG anti-BP180 antibodies were positive in 63 (94%) of 67BP patients. IgG anti-BP230, IgE anti-BP180, and IgE anti-BP230 antibodies were found in 48 (72%), 20 (30%) and 45 (67%), respectively. IgG anti-BP180 levels were correlated with the affected areas. IgG anti-BP230 antibodies tended to increase in proportion to elongation of disease duration. IgE anti-BP230 levels showed a strong association with local eosinophil accumulation, while the levels were reversely related with the affected areas in BP.

CONCLUSIONS

IgE autoantibodies to BP180 and BP230 are detected at high frequencies in BP. IgE anti-BP230 antibodies may have a role in attracting eosinophils to the skin lesions.

Quantification of antineural antibodies in autoimmune neurological disorders

More than 50 different neurological pathologies have a confirmed or suspected autoimmune etiology affecting an estimated number of 75 million people worldwide. Autoantibodies are a useful diagnostic marker for most autoimmune diseases even though their pathological role is not evident, and several tests for their detection are commercially available. However, for autoimmune diseases involving the nervous system, lack of clear information on the identity of antineural antibody targets and the presence of many rare diseases have hampered the development of specific diagnostic assays. This review focuses on the actual knowledge on confirmed and suspected autoimmune diseases that target the CNS and the diagnostic relevance of corresponding antineural autoantibodies.

Experimental models for the autoimmune and inflammatory blistering disease, Bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal skin blistering disease characterized immunohistologically by dermal-epidermal junction (DEJ) separation, an inflammatory cell infiltrate in the upper dermis, and autoantibodies targeted toward the hemidesmosomal proteins BP230 and BP180. Development of an IgG passive transfer mouse model of BP that reproduces these key features of human BP has demonstrated that subepidermal blistering is initiated by anti-BP180 antibodies and mediated by complement activation, mast cell degranulation, neutrophil infiltration, and proteinase secretion. This model is not compatible with study of human pathogenic antibodies, as the human and murine antigenic epitopes are not cross-reactive. The development of two novel humanized mouse models for the first time has enabled study of disease mechanisms caused by BP autoantibodies, and presents an ideal in vivo system to test novel therapeutic strategies for disease management.

A pathogenic role for IgE in autoimmunity: bullous pemphigoid IgE reproduces the early phase of lesion development in human skin grafted to nu/nu mice

Bullous pemphigoid (BP) is an autoimmune disease characterized by subepidermal blistering. Based on previous work, IgG autoantibodies directed against BP180 are thought to be the primary pathogenic agent in BP. In addition to these IgG autoantibodies, however, most BP patients produce IgE class autoantibodies that also react with BP180, and total IgE levels are often elevated in this disease. To directly test whether BP IgE is pathogenic, 6 ng of total IgE isolated from two BP and two normal sera were injected into human skin grafted onto athymic, nude mice. Twenty-four hours after injection, erythematous, elevated plaques were observed in all human skin grafts receiving BP IgE (n=11), but not control IgE (n=9). Histologic and ultrastructural examination of the lesions showed engorgement of blood vessels and a dermal infiltrate composed of neutrophils, eosinophils, and mast cells, many of which were degranulated. At a higher dose of BP IgE (47 ng), histological separation of the epidermis from the dermis was observed in two of the three grafts. The BP IgE-induced erythematous plaques were reminiscent of those clinically seen in BP. This provides early evidence of a direct demonstration of a pathogenic role for IgE class autoantibodies in a human autoimmune disease.

Experimental models of epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is an organ-specific autoimmune disease with a well-defined antigen-autoantibody system. Recently, mutually complementary ex vivo and animal models were developed for this disease. The blister formation of EBA can be reproduced by passively transferring antibodies against type VII collagen into mice. In addition, the Fc-dependent interaction of autoantibodies with granulocytes resulting in dermal-epidermal separation can be studied using patient autoantibodies and leukocytes from healthy donors in cryostat sections of normal human skin. Finally, the autoimmune response and the active blistering disease are replicated by immunizing mice with autologous type VII collagen. The results obtained using these experimental systems provided conclusive evidence that EBA is an antibody-mediated autoimmune disease. In addition, these models represent powerful new tools for understanding EBA pathophysiology and will likely offer unique opportunities to investigate the molecular mechanisms of antibody-mediated autoimmune diseases in general. Thus, due to improved disease modelling, EBA emerges as an exquisitely instructive model disease to study fundamental, biologically and clinically crucial aspects of antibody-mediated organ-specific autoimmune diseases that extend well beyond the limits of autoimmunity against type VII collagen. The new mechanistic insights gained from investigating EBA pathogenesis will facilitate the design of immunomodulatory interventions for this and other pathogenetically related organ-specific, antibody-dependent autoimmune diseases.

Bullous pemphigoid: physiopathology, clinical features and management

There has been a considerable progress in the understanding of the physiopathology of BP during the past 2 decades. The insights into the humoral and cellular immune response against BP180 and BP230 have increased significantly. Nevertheless, the factors underlying the initiation of the disease leading to a disruption of self-tolerance remain unclear. Clinically, the disease shows protean presentations, and diagnostic delay is common. A practical, relevant, and unresolved question is how to identify patients suffering from BP at an early stage of the disease, when direct immunofluorescence microscopy findings still may be negative. The characterization of markers allowing the differentiation of BP from other pruritic eruptions occurring in the elderly population would be extremely helpful in daily practice. Finally, despite the knowledge that potent topical steroids are efficient in controlling the disease, management of BP sometimes remains difficult and requires systemic therapies. It is hoped that a better knowledge of the regulation of the autoimmune response in BP also will facilitate the design of novel immunomodulatory therapeutic approaches devoid of the severe side effects of current immunosuppressive treatments.