Bullous skin diseases

Association of specific HLA alleles and haplotypes with pemphigus vulgaris in the Bulgarian population

Pemphigus vulgaris (PV) is an autoimmune bullous dermatosis with uneven geographic distribution and higher incidence in certain populations. In previous studies, a relatively high incidence of PV was reported in Bulgaria (0.47/100,000/year) comparable to that in other countries. The genetic background was considered responsible for the disease susceptibility, and multiple reports have proven PV to be an HLA-associated condition. The aim of our study was to analyze the role of genetic factors in the development of PV in Bulgaria. HLA genotyping was performed in 56 PV patients, ethnic Bulgarians whose diagnosis was confirmed based on clinical, histological, and immunofluorescent findings. The control group consisted of 204 healthy individuals from the Bulgarian population without evidence for HLA-associated autoimmune diseases. HLA-A,-B,-DRB1,-DQB1 analysis was performed by PCR-SSP. Our results revealed predisposing associations with DRB1*14, DRB1*04:02, and B*38, B*55, while allele DRB1*03:01 and the corresponding haplotypes were significantly decreased in the PV patients. The predisposing role of these alleles has been observed in other populations. All reported predisposing DRB1 alleles have the same amino acids at key positions of the beta chain of the HLA molecules, 26 (Phe), 67 (Leu or Ileu), 70 and 71 (hydrophobic AA: Gln, Arg, Asp, or Glu), and 86 (Val), which is important for the selective presentation of desmoglein 3 peptides. Additionally, specific alleles HLA-A*01 and DRB1*11 were identified with decreased frequencies in the patients’ group, the last one being a common protective allele for autoimmune diseases in the Bulgarian population. The elucidation of the role of genetic factors for the development of pemphigus will help explain its higher incidence and clinical variability in certain populations.

Integrated, multicohort analysis reveals unified signature of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease that follows an unpredictable disease course and affects multiple organs and tissues. We performed an integrated, multicohort analysis of 7,471 transcriptomic profiles from 40 independent studies to identify robust gene expression changes associated with SLE. We identified a 93-gene signature (SLE MetaSignature) that is differentially expressed in the blood of patients with SLE compared with healthy volunteers; distinguishes SLE from other autoimmune, inflammatory, and infectious diseases; and persists across diverse tissues and cell types. The SLE MetaSignature correlated significantly with disease activity and other clinical measures of inflammation. We prospectively validated the SLE MetaSignature in an independent cohort of pediatric patients with SLE using a microfluidic quantitative PCR (qPCR) array. We found that 14 of the 93 genes in the SLE MetaSignature were independent of IFN-induced and neutrophil-related transcriptional profiles that have previously been associated with SLE. Pathway analysis revealed dysregulation associated with nucleic acid biosynthesis and immunometabolism in SLE. We further refined a neutropoiesis signature and identified underappreciated transcripts related to immune cells and oxidative stress. In our multicohort, transcriptomic analysis has uncovered underappreciated genes and pathways associated with SLE pathogenesis, with the potential to advance clinical diagnosis, biomarker development, and targeted therapeutics for SLE.

Detection of pemphigus desmoglein 1 and desmoglein 3 autoantibodies and pemphigoid BP180 autoantibodies in saliva and comparison with serum values

Although there is much literature on the detection of pemphigus and pemphigoid autoantibodies by enzyme-linked immunosorbent assay (ELISA) in serum, nothing is known about their presence in saliva. The aim of this study was to evaluate the salivary levels of these autoantibodies in pemphigus and pemphigoid patients. Autoantibodies against desmoglein3, desmoglein1, and BP180 were assayed, by ELISA, in serum and saliva samples of patients and healthy controls. The titres of autoantibodies against Dsg1/3 found in both serum and saliva of pemphigus patients showed a statistically significant correlation, suggesting that saliva may be a useful biological material for diagnostic purposes, in monitoring disease activity, as well as for the early detection of relapses. By contrast, the titres of autoantibodies against BP180 in the serum and saliva of bullous pemphigoid patients were not statistically related, and further study of the usefulness of the BP180 ELISA for saliva in this disease is needed. In addition, based on our results, the BP180 ELISA with a recombinant NC16a epitope failed to detect the autoantibodies against BP180 in the serum and saliva of mucous membrane pemphigoid patients.

Number III Mucous membrane pemphigoid

Mucous membrane pemphigoid (MMP) is a sub-epithelial vesiculobullous disorder. It is now quite evident that a number of sub-epithelial vesiculobullous disorders may produce similar clinical pictures, and also that a range of variants of MMP exist, with antibodies directed against various hemidesmosomal components or components of the epithelial basement membrane. The term immune-mediated sub-epithelial blistering diseases (IMSEBD) has therefore been used. Immunological differences may account for the significant differences in their clinical presentation and responses to therapy, but unfortunately data on this are few. The diagnosis and management of IMSEBD on clinical grounds alone is impossible and a full history, general, and oral examination, and biopsy with immunostaining are now invariably required, sometimes supplemented with other investigations. No single treatment regimen reliably controls all these disorders, and it is not known if the specific subsets of MMP will respond to different drugs. Currently, apart from improving oral hygiene, immunomodulatory-especially immunosuppressive-therapy is typically used to control oral lesions. The present paper reviews pemphigoid, describing the present understanding of this fascinating clinical phenotype, summarising the increasing number of subsets with sometimes-different natural histories and immunological features, and outlining current clinical practice.

Transient CD44 variant isoform expression and reduction in CD4(+)/CD25(+) regulatory T cells in C3H/HeJ mice with alopecia areata

Alopecia areata, an autoimmune disease affecting anagen stage hair follicles, can be induced by grafting spontaneous alopecia areata affected skin to normal-haired C3H/HeJ mice. As the onset of alopecia areata can be significantly retarded by anti-CD44 variant isoform 10 treatment, it was interesting to explore the underlying disease mechanism. Two weeks after transplanting alopecia areata affected skin, expression of CD44 variant isoforms 3, 6, 7, and 10 was strikingly upregulated as compared with sham-grafted mice. By 6 wk after grafting, CD44 variant isoform levels had returned to normal, whereas in draining lymph nodes, CD44 variant isoform expression was slightly decreased. Leukocytes in the skin of mice with chronic alopecia areata expressed a hematopoietic isoform of CD44 and CD44 variant isoform 6 at an elevated level, but CD44 variant isoform 3 expression was reduced. Cytokine expression in leukocytes of chronic alopecia areata affected skin was higher than in normal-haired controls. Cytokine expression also increased postsurgery in sham and alopecia areata grafted mice, but remained elevated only in mice receiving alopecia areata affected skin. Finally, from the skin of mice with chronic alopecia areata and of mice transplanted with alopecia areata affected skin, an increased number of CD4(+) and CD8(+) cells, but a strongly decreased number of CD4(+)/CD25(+) regulatory T cells was recovered. Thus, expression of CD44 variant isoforms is important for the migration of leukocytes during the initial period of alopecia areata. CD44, however, is apparently not involved in the maintenance of the disease state, which is characterized by high cytokine expression levels, an increased number of CD4(+) and CD8+ cells, but a low level of CD4(+)/CD25(+) suppressor cells.

Cicatricial pemphigoid with circulating autoantibodies to beta4 integrin, bullous pemphigoid 180 and bullous pemphigoid 230

Cicatricial pemphigoid is a heterogeneous group of autoimmune subepidermal blistering diseases associated most commonly with autoantibodies to bullous pemphigoid (BP)180 and less frequently with those to laminin 5 or type VII collagen. In addition, a few cases have been described with autoantibodies to the beta4 subunit of alpha6beta4 integrin. We describe a patient with extensive disease of ocular, oral, pharyngeal, laryngeal and genital mucous membranes that healed with scarring of conjunctivae. IgG autoantibodies bound to the dermal-epidermal junction on direct immunofluorescence (IF) microscopy and to the epidermal side of 1 mol L(-1) NaCl-split skin on indirect IF microscopy. Our patient's circulating IgG recognized a 205-kDa protein in extracts of 293T cells transfected with the beta4 subunit of alpha6beta4 integrin and in the cell extract of DJM-1 cells. Our patient's IgG and IgA autoantibodies also reacted with full-length BP180 derived from epidermal extracts and the ectodomain of BP180 (LAD-1) derived from culture supernatant of keratinocytes. In addition, a weak IgG reaction with BP230 was noted. The disease rapidly responded to dexamethasone-cyclophosphamide pulse therapy, and immunoblot reactivity to both beta4 integrin and BP180 decreased according to disease activity.

Increase of oxidatively modified protein is associated with a decrease of proteasome activity and content in aging epidermal cells

For the process of aging in epidermal cells to be characterized, the status of oxidized and damaged protein accumulation and removal by the proteasome has been investigated. Modified protein content and proteasome activity were assayed in lysates of epidermal cells from donors of different ages. Increased levels of oxidized proteins, glycated proteins, and proteins modified by the lipid peroxidation product 4-hydroxy-2-nonenal were observed in cells from old donors. At the same time, a decline of chymotrypsin-like and peptidylglutamyl-peptide hydrolase activities of the proteasome was found in aging keratinocytes. This age-related decline of the proteasome peptidase activities can be explained, at least in part, by a decreased proteasome content as observed by immunoblotting and enzyme-linked immunosorbent assay. In keratinocyte cultures, a decrease of proteasome activity and content was observed upon serial passaging. In cultures, as well as in skin, an inverse relationship was found between the aging marker 1-galactosidase and the proteasome content. These results suggest that proteasome is downregulated during replicative senescence as well as in aged cells in vivo, possibly resulting in the accumulation of modified proteins.

A subepidermal bullous eruption associated with IgG autoantibodies to a 200 kd dermal antigen: the first case report from the United States

We describe an 81-year-old white man in whom a subepidermal bullous eruption developed that clinically resembled bullous pemphigoid. The eruption promptly responded to oral tetracycline and niacinamide and topical clobetasol. Histologic examination of perilesional skin revealed neutrophilic infiltration with formation of papillary microabscesses and subepidermal cleavage. Direct immunofluorescence showed linear deposition of IgG and C3 along the basement membrane zone. By indirect immunofluorescence, circulating IgG autoantibodies bound exclusively to the dermal side of salt-split normal human skin. Immunoblot analysis demonstrated that the patient's autoantibodies reacted with a 200 kd dermal protein that was different from type VII collagen, the epidermolysis bullosa acquisita autoantigen. This patient represents the first confirmed case from the United States with a recently reported novel autoimmune subepidermal bullous disease associated with IgG autoantibodies to a 200 kd dermal antigen.

Non-plaque-induced gingival lesions

The origin of gingival inflammation is occasionally different from that of routine plaque-associated gingivitis, and such non-plaque-associated types of gingivitis often present characteristic clinical features. Examples of such forms of gingivitis are specific bacterial, viral, and fungal infections. Specific bacterial infections of gingiva may be due to Neisseria gonorrhea, Treponema pallidum, streptococci, and other organisms. The most important viral infections of gingiva are herpes simplex virus type 1 and 2 and varicella-zoster virus. Fungal infections may be caused by several fungi, the most important of these being Candida species including C. albicans, C. glabrata, C. krusei, C. tropicalis, C. parapsilosis, and C. guillermondii. Gingival histoplasmosis is a granulomatous disease caused by the fungus Histoplasma capsulatum and, as for the other specific infections of gingiva, a confirmed diagnosis may require histopathologic examination and/or culture. Atypical gingivitis may also occur as gingival manifestations of dermatological diseases, the most relevant of these being lichen planus, pemphigoid, pemphigus vulgaris, erythema multiforme, and lupus erythematosus. Non-plaque induced gingival inflammation can be caused by allergic reactions to dental restorative materials, toothpastes, mouthwashes, and foods. In addition, gingival inflammation may result from toxic reactions, foreign body reactions, or mechanical and thermal trauma.

Pemphigus and bullous pemphigoid

Pemphigus and bullous pemphigoid are distinct autoimmune blistering diseases that are characterised by the presence of autoantibodies directed against specific adhesion molecules of the skin and mucous membranes. The comparison and contrast of molecular mechanism of blister formation of these two diseases provide a rational diagnostic and therapeutic approach to affected patients.

Update on mucous membrane pemphigoid: a heterogeneous immune-mediated subepithelial blistering entity

Most oral involvement in the skin diseases (dermatoses) is related to mucous membrane pemphigoid or lichen planus. Mucous membrane pemphigoid was the subject of a European Symposium held in Turin, Italy, in June 1997. This review is based on that symposium. Mucous membrane pemphigoid is a subepithelial vesiculobullous disorder mainly of late middle age; it has a slight predilection for women. Whereas mucous membrane pemphigoid was formerly considered a single entity, it is now quite evident that a number of subepithelial vesiculobullous disorders may produce similar clinical pictures and also that a range of variants of mucous membrane pemphigoid exists, with antibodies directed against various hemidesmosomal components or components of the epithelial basement membrane. The term immune-mediated subepithelial blistering diseases has therefore been used. Diagnosis and management of immune-mediated subepithelial blistering diseases on clinical grounds alone are impossible; a full history, general and oral examinations, and biopsy with immunostaining are now invariably required, sometimes supplemented with other investigations. Most patients with mucous membrane pemphigoid affecting the mouth manifest desquamative gingivitis, a fairly common complaint typically seen in women who are middle-aged or older. Oral vesicles and erosions may also occur, and there can be a positive Nikolsky sign. Some patients have lesions of other stratified squamous epithelia, presenting as conjunctival, nasal, oesophageal, laryngeal, vulval, penile, or anal involvement. Apart from improving oral hygiene, immunomodulatory-in particular, immunosuppressive-therapy is typically required to control oral lesions in mucous membrane pemphigoid. No single treatment regimen reliably controls all these disorders.

Subepidermal autoimmune bullous skin diseases associated with B-cell lymphoproliferative disorders

The development of several types of autoimmune disorders is well known in the course of B-cell lymphoproliferative diseases. In order to investigate whether these autoimmune diseases may target cutaneous antigens, especially those of the dermal-epidermal junction, we conducted a retrospective analysis of all cutaneous direct immunofluorescence studies performed in patients with B-cell neoplasia who presented with cutaneous lesions requiring a skin biopsy. Patients with linear deposits of immunoglobulin or C3 molecules at the dermal-epidermal junction were studied further, using immunoblotting and immunoelectron microscopy. Patients with no overt hematologic malignancies but with cutaneous lesions requiring direct immunofluorescence were studied as a control population. During the study period, the diagnosis of autoimmune blistering diseases of the dermal-epidermal junction was established in 9/102 (8.9% +/- 2%) patients with a B-cell lymphoid disorder, compared with 288/8,189 (3.5% +/- 0.04%) patients without underlying hemopathy (p < 0.01). Among the 9 patients, 7 were studied in detail. Immunologic studies demonstrated epidermolysis bullosa acquisita in 6 patients and cicatricial pemphigoid in 1. Autoimmune blistering diseases, especially epidermolysis bullosa acquisita, are part of the spectrum of autoimmune disorders associated with B-cell neoplasia.

Common human leukocyte antigen alleles in pemphigus vulgaris and pemphigus foliaceus Italian patients

Pemphigus refers to a group of autoimmune blistering skin diseases, mainly identified as pemphigus vulgaris and pemphigus foliaceus, both characterized by the presence of autoantibodies against keratinocyte adhesion molecules, leading to loss of cell-cell adhesion with consequent blister formation. Pemphigus vulgaris is reported to be associated with human leukocyte antigen DR4 and/or DR6 whereas no data are available on pemphigus foliaceus, except for the endemic Brazilian form (fogo selvagem), which is reported to be associated with DR1 and DR4. We here report human leukocyte antigen molecular typing on a total of 87 patients, 61 with pemphigus vulgaris and 26 with pemphigus foliaceus, versus 128 healthy matched controls. Generic typing showed an increase of DRB1*04 and DRB1*14 and a decrease of DRB1*07 in both pemphigus vulgaris and pemphigus foliaceus patients. Molecular subtyping of DR4+ and DR14+ subjects showed a highly significant association between the DRB1*1401 and both pemphigus vulgaris (p < 0.0001) and pemphigus foliaceus patients (p < 0.0001) together with a significant increase of the linked DQB1*0503 (pemphigus vulgaris p < 0.0001; pemphigus foliaceus p < 0.0001). Moreover, whereas the association between DRB1*0402 and pemphigus vulgaris (p < 0.0001) has been confirmed, no significant association between a specific allele of the DR4 group and pemphigus foliaceus, has been found. Therefore, at least in Italian patients, pemphigus vulgaris and pemphigus foliaceus share DRB1*1401 and DQB1*0503, as susceptible human leukocyte antigen alleles, whereas DRB1*0402 is only found associated with pemphigus vulgaris. The observation that both diseases, pemphigus vulgaris and pemphigus foliaceus, carry the same susceptible human leukocyte antigen alleles has been interpreted as a common genetic background predisposing to pemphigus as, like in other autoimmune disorders, it is not sufficient to explain the onset of the disease on the basis of the sole aforementioned alleles. Other linked genes and/or environmental factors should play a facilitating role in the outbreak of pemphigus, either pemphigus vulgaris or pemphigus foliaceus.

Human leucocyte antigen class II associations in chronic idiopathic urticaria

The major histocompatibility complex (MHC) acts as a marker for self during T-cell ontogeny and is associated with the pathogenesis of many autoimmune diseases. Recent investigations have shown about 30% of patients with chronic idiopathic urticaria (CIU) have IgG autoantibodies against the high-affinity IgE receptor, FcepsilonRI, or IgE. A link between MHC class II alleles and CIU has not been reported previously. DNA was extracted from blood of 100 Caucasian patients with CIU, and the MHC class II type determined using the polymerase chain reaction with sequence-specific primers, testing for DRB and DQB1 alleles. The frequency of alleles in CIU patients was compared with that found in 603 controls. Further human leucocyte antigen (HLA) typing on patient subsets, classified by the patients' responses to intradermal injection of autologous serum and their serum-induced histamine release from basophil leucocytes of healthy donors, was undertaken. HLA DRB1*04 (DR4) and its associated allele, DQB1*0302 (DQ8), are raised in CIU patients compared with a control population (P = 2 x 10-5 and P = 2 x 10-4, respectively). HLA DRB1*15 (DR15) and its associated allele, DQB1*06 (DQ6), are significantly less frequently associated with CIU. The HLA DRB1*04 association is particularly strong (corrected P = 3.6 x 10-6) for patients whose serum has in vivo and in vitro histamine-releasing activity. HLA class II typing is consistent with the concept that CIU is a heterogeneous disease, and supports an autoimmune pathogenesis in a subset of patients.

Hemidesmosomal molecular changes in dermatitis herpetiformis; decreased expression of BP230 and plectin/HD1 in uninvolved skin

Recent BP230-knockout experiments with subsequent blistering and recently identified plectin/HD1 mutations in epidermolysis bullosa simplex patients suggest that defective expression of BP230 and plectin/HD1 may predispose to blister formation in human skin. We have studied the expression of the epithelial adhesion complex as well as the basement membrane and anchoring fibril antigens in uninvolved dermatitis herpetiformis skin to find out if alterations can be detected in these structures predisposing to the blister formation typical of the disease. Ten uninvolved dermatitis herpetiformis skin specimens, which all showed clear granular deposits of IgA under the basement membrane in direct immunofluorescence and five normal skin specimens, were studied by indirect immunofluorescence technique. Six uninvolved dermatitis herpetiformis skin specimens showed distinctly decreased immunoreaction for BP230 and four uninvolved dermatitis herpetiformis skin specimens showed distinctly decreased immunoreaction for plectin/HD1. All five skin controls showed strong immunoreactions for BP230 and plectin/HD1. Other hemidesmosomal proteins including BP180 and integrin alpha6beta4, as well as basement membrane proteins laminin-5, laminin-1, nidogen and type IV collagen, and the anchoring fibril protein type VII collagen showed a normal strong expression. Our results suggest that alterations in BP230 and plectin/HD1 may contribute or predispose to blister formation in dermatitis herpetiformis skin.

Clinical, demographic, and immunohistologic features of vancomycin-induced linear IgA bullous disease of the skin. Report of 2 cases and review of the literature

Administration of intravenous vancomycin has been associated with the development of linear IgA bullous disease (LABD). In contrast to the idiopathic variant, vancomycin-induced LABD (VILABD) appears to be more transient and to be associated with lower morbidity. The characteristics of this entity remain undefined. Our analysis of clinical, demographic, and immunopathologic features of 2 new and 14 previously reported patients with VILABD reveals that VILABD is clinically and immunopathologically indistinguishable from its idiopathic variant. A variety of premorbid conditions and concomitant medications were observed, none of which was consistently associated with the development of VILABD. VILABD occurs independently of vancomycin trough levels, resolves promptly upon discontinuation of vancomycin, and recurs more severely and with shorter onset latency with vancomycin rechallenge. This entity should be recognized as 1 of the adverse cutaneous effects of intravenous vancomycin, and warrants prompt diagnosis through direct immunofluorescence skin examination.

Molecular characterization of an autoallergen, Hom s 1, identified by serum IgE from atopic dermatitis patients

Atopy is a genetically determined disorder that affects 10%-20% of the population. Many symptoms of patients with atopy (allergic rhinitis, conjunctivitis, asthma, and anaphylaxis) result from events occurring after crosslinking of cell-bound IgE by per se innocuous environmental antigens. The frequently raised hypothesis that autosensitization can also be a pathogenetic factor in atopy, gained support by our recent demonstration of IgE antibodies against human proteins in atopic dermatitis patients. To unravel the molecular nature of IgE-defined autoantigens, we used serum IgE from atopic dermatitis patients to screen a human epithelial cDNA expression library. One of the cDNA-encoding IgE-reactive products contained 1501 bp of a 2274 bp open-reading frame finally identified by sequence analysis of two additional cDNA clones resulting from oligonucleotide screening. The IgE-defined autoantigen, designated Hom s 1, exhibited an almost complete sequence identity with a recently described antigen recognized by cytotoxic T cells of a squamous cell carcinoma patient. Purified recombinant Hom s 1 specifically bound IgE from patients with severe atopy. When used as immunogen in rabbits, recombinant Hom s 1 gave rise to an anti-serum that reacted with a cytoplasmic protein exhibiting a broad cellular and tissue reactivity (skin, lung >> gastrointestinal tract >> muscle, brain) and identified a 55 kDa protein in blotted serum IgE preparations. The attractive possibility remains that the Hom s 1-triggered IgE response contributes to the events resulting in allergic tissue inflammation. If so, the respective recombinant molecule may serve as a paradigmatic tool for the diagnosis and treatment of patients with "intrinsic" atopy.

CD44 variant isoform expression in a variety of skin-associated autoimmune diseases

CD44 variant isoforms are frequently expressed on tissue-infiltrating lymphocytes. By the high incidence of autoimmune reactions of the skin and aiming at new strategies of therapeutic intervention, we became interested in evaluating the CD44 isoform expression profile in autoimmune reactions of the skin. Expression of CD44s, CD44v3, v5, v6, v7, v7-v8, and v10 was evaluated in 55 biopsies of lupus erythematosus, bullous pemphigoid, vasculitis, morphea, and pemphigus vulgaris. Biopsies did not contain CD44v5-, CD44v6-, CD44v7-, or CD44v7-v8-positive leukocytes. Staining with anti-CD44v10 was seen in vasculitis and occasionally in lupus erythematosus, morphea, and bullous pemphigoid. All biopsies contained CD44v3(+) leukocytes, the percentage of CD44v3(+) leukocytes being increased in autoimmune infiltrates with the exception of pemphigus vulgaris. CD44v3 was expressed by CD4(+) cells as well as by part of CD8(+) cells, Langerhans cells, and monocytes. Vascular endothelium also contained CD44v3(+) cells. Only monocytes expressed CD44v10. We assume that CD44v3 and CD44v10 may be targeting leukocytes toward the skin or allow for their retention and expansion via binding of cytokines and chemokines harbored by activated, skin-associated endothelium or provided by cells surrounding the infiltrate. The absence of CD44v6, frequently associated with lymphocyte activation, appears to be a peculiarity of skin-infiltrating leukocytes.

Self-reactive B cells are not eliminated or inactivated by autoantigen expressed on thyroid epithelial cells

Graves' Disease results from the production of autoantibodies against receptors for thyroid stimulating hormone (TSH) on thyroid epithelial cells, and represents the prototype for numerous autoimmune diseases caused by autoantibodies that bind to organ-specific cell membrane antigens. To study how humoral tolerance is normally maintained to organ-specific membrane antigens, transgenic mice were generated selectively expressing membrane-bound hen egg lysozyme (mHEL) on the thyroid epithelium. In contrast to the deletion of autoreactive B cells triggered by systemic mHEL (Hartley, S.B., J. Crosbie, R. Brink, A.B. Kantor, A. Basten, and C.C. Goodnow. 1991. Nature. 353:765-769), selective expression of mHEL autoantigen on thyroid cells did not trigger elimination or inactivation of circulating HEL-reactive B cells. These results provide evidence that tolerance is not actively acquired to organ-specific antigens in the preimmune B cell repertoire, underscoring the importance of maintaining tolerance to such antigens by other mechanisms. The role of an intact endothelial barrier in sequestering organ-specific antigens from circulating preimmune B cells is discussed.