The distribution of IgG subclass autoantibodies in bullous pemphigoid analysed by immunofluorescence and immunoblotting

Bullous Pemphigoid: A 10-Year Study of Discordant Results on Direct Immunofluorescence

Background:

Bullous pemphigoid (BP) is the most common subepidermal autoimmune disorder characterized by tense bullae. It is associated with circulating autoantibodies against BP antigen-1 and BP antigen-2. Diagnosis is based upon clinical, histopathologic, and immunopathologic examination. Direct immunofluorescence (DIF) of perilesional skin highlights C3 with or without IgG in a linear pattern along the basement membrane.

Objectives:

We hypothesized that repeat biopsies may be required for a definitive DIF diagnosis of BP, as initial DIF evaluation may result in a false-negative result.

Methods:

A retrospective chart review was conducted on 1143 specimens collected for evaluation for BP. Cases from 2 Vancouver Coastal Health Authority laboratories from 2006 to 2016 were reviewed. Results were interpreted as positive, negative, or indeterminate based on pathologic description and specimen quality.

Results:

After meeting the inclusion criteria, 739 specimens were further evaluated. There were 289 cases of BP in the 10-year period. Five patients (1.73%; 95% confidence interval [CI], 1.50-1.96) required a second biopsy to support a BP diagnosis, and within this group, 1.04% of the 289 (95% CI, 0.811-1.27) were true successive negative-to-positive DIF results.

Conclusions:

DIF is the most reliable test used to diagnose BP; however, a small percentage of patients will initially have a negative result. False-negative or indeterminate results may be due to specimen sampling from lesional skin or due to a subthreshold quantity of immune complexes in the skin. Repeat biopsy is warranted despite an initial negative DIF if BP is clinically suspected.

IgG4 as the predominant IgG subclass in pemphigoides gestationis

BACKGROUND

Pemphigoides gestationis (PG) is a blistering disorder of pregnancy caused by antibodies against basement membrane proteins. They are directed against the 180 kD bullous pemphigoid antigen (BPAg2), towards the epitopes within the NC 16A domain. There are many similarities between pemphigoid gestationis and bullous pemphigoid (BP), but the literature so far indicated different immunofluorescence results in regards with C3 and IgG, and IgG subclasses (IgG4 vs. IgG1).

METHODS

We evaluated staining patterns and IgG subclasses, as well as C5b-9 membrane attack complex (MAC) in 10 pregnant patients with PG, using sandwich double antibody immunofluorescence (SDAI) and direct immunofluorescence (DIF).

RESULTS

All ten specimens stained with C3 by DIF, but only five had trace amount of IgG reactants by this method. By SDAI, 100% were positive for the IgG4 and C5b-9 MAC, 70% for IgG2, 50% for IgG1, and 40% for IgG3.

CONCLUSION

IgG4 was the predominant IgG subtype identified. This finding has not been reported for PG, but it mimics results reported for BP. One explanation is prolonged disease course, as well as blocking of antigenic domains by IgG4. Understanding this completely will help develop therapies and prevention strategies for immunobullous and other autoimmune diseases, and perhaps aid in an exact classification.

A predominant IgG4 subclass may be responsible for false-negative direct immunofluorescence in bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is an immune-mediated blistering disease, usually characterized immunopathologically by the linear deposition of IgG and C3 along the basement membrane zone (BMZ) of skin. However, positive deposition of C3 but negative staining for IgG on direct immunofluorescence (DIF) studies has been noted in some patients.

METHODS

Twelve patients known to have BP but with absence of staining for IgG were included in this study. Frozen sections of skin specimens from the 12 patients were subjected to IgG DIF, as well as a sandwich double antibody method of staining for IgG, IgG subclasses, and light chains. Enzyme-linked immunosorbent assay (ELISA) using commercially available human IgG subclasses was used to analyze the subclass restriction of FITC-labeled antihuman IgG conjugates.

RESULTS

Of the 12 skin specimens with positive C3 and negative IgG on DIF, nine were positive for IgG with the double antibody sandwich method. In addition, all 12 specimens had positive linear staining for the subclass IgG4 along the BMZ with this method. There was no IgG light chain restriction. Two commercially obtained antihuman IgG conjugates, both commonly used in our laboratory for DIF testing, were analyzed for separate IgG subclass specificity by ELISA. Both conjugates showed high reactivity to IgG1 and IgG3 with less reactivity to IgG2 and IgG4.

CONCLUSION

These results suggest that the following factors contribute to false-negative staining for IgG on DIF in some BP patients: (i): subthreshold IgG in skin specimens; (ii) limited reactivity of commercial antihuman IgG conjugates to the IgG4 subclass; and (iii) decreased sensitivity of DIF compared with double antibody methods for the detection of IgG. The use of sandwich double antibody immunofluorescence methods to test for IgG and/or IgG subclasses may be helpful in definitively diagnosing BP in patients with negative IgG and positive C3 staining on DIF.

Autoantibodies to the extracellular and intracellular domain of bullous pemphigoid 180, the putative key autoantigen in bullous pemphigoid, belong predominantly to the IgG1 and IgG4 subclasses

BACKGROUND

Autoantibodies to the extracellular domain (ECD) of bullous pemphigoid (BP) antigen 180 (BP180) are thought to play a crucial part in the pathophysiology of BP.

OBJECTIVES

As the various IgG subclasses have different biological properties, we have sought to assess the relative isotype distribution of IgG to BP180 and their reactivity against the ECD and intracellular domain (ICD) of BP180.

METHODS

The reactivity of 27 sera from patients with BP was assayed by immunoblotting against recombinant proteins covering the ECD and ICD of BP180.

RESULTS

Twenty-seven (100%) and 21 (77%) of 27 BP sera, respectively, contained IgG1 and IgG4 autoantibodies binding to the ECD of BP180. Fourteen (82%) and six (35%) of the 17 BP sera that were reactive with the ICD of BP180 had autoantibodies of the IgG1 and IgG4 subclass, respectively. The profile of the isotype restriction appeared to be similar when the response to the ECD vs. that to the ICD was compared. IgG2 and IgG3 reactivity with BP180 was found less frequently. Patients with BP of longer duration showed a tendency to have, in addition to IgG1, an IgG4 response.

CONCLUSIONS

Consistent with prior evidence indicating that subepidermal blister formation in BP is dependent upon complement activation, the frequent finding of complement-fixing IgG1 autoantibodies to both the ECD and ICD of BP180 might have pathogenic relevance in BP. These findings provide new insights relevant for our understanding of the immune response to BP180, the putative key autoantigen in BP.

IgG autoantibodies from bullous pemphigoid patients recognize multiple antigenic reactive sites located predominantly within the B and C subdomains of the COOH-terminus of BP230

Bullous pemphigoid is a subepidermal bullous disorder characterized by an autoantibody response against the bullous pemphigoid antigen 230 (BP230) and the bullous pemphigoid antigen 180 (BP180), a cytoplasmic component and a transmembrane component, respectively, of hemidesmosomes. Although immunodominant sequences within the extracellular domain of BP180 have been identified, characterization of the antigenic sites on BP230 is still incomplete. To identify autoantibody-reactive sites on BP230 and to examine whether the targeted regions are contained within functionally important domains, recombinant fragments encompassing almost the entire BP230 were used to assess the reactivity of 25 bullous pemphigoid sera by immunoblotting. Our results demonstrate that (i) the region bearing the B and C subdomains of the COOH-terminus of BP230 contains immunodominant sequences recognized by the majority of bullous pemphigoid sera; (ii) additional autoantibody- reactive sites are present over extended regions of the NH2-terminal half of BP230 without evidence for antigenic cross-reactivity between the NH2- and COOH-termini of BP230; and, finally, (iii) autoantibodies reacting with the BP230 tail predominantly belong to the IgG4 and IgG1 subclasses, suggesting that both autoreactive TH2 and autoreactive TH1 cells regulate the autoantibody response to immunodominant sequences of BP230. As the COOH- terminus of BP230 mediates the attachment of keratin intermediate filaments to the hemidesmosomal plaque, whereas its NH2-terminus contains sequences important for its interaction with other constituents of hemidesmosomes, autoantibodies to BP230 might precipitate subepidermal blister formation and perpetuate the disease not only by eliciting an inflammatory reaction but also by interfering with the function of BP230 and thus the stability of hemidesmosomes.

Bullous pemphigoid IgG2 and IgG4 antibodies have a capability to inhibit a transient increase of intracellular Ca2+ induced by bullous pemphigoid IgG1 antibody

To elucidate the role of Bullous pemphigoid (BP) IgG subclasses in the transmembrane signal transduction of keratinocytes, we examined whether BP IgG2 or IgG4 inhibits the intracellular Ca2+ concentration ([Ca2+]i) increase induced by BP IgG1. IgG2 from one of five BP patients inhibited the increase of [Ca2+]i in human squamous cell carcinoma cell line; DJM-1 cells induced by BP IgG1. IgG4 from two of four BP patients inhibited the increase of [Ca2+]i induced by BP IgG1. In addition, a two fold quantity of IgG2 inhibited the increase of [Ca2+]i induced by BP IgG1. A two fold quantity of IgG4 from two of five BP patients inhibited the increase of [Ca2+]i induced by BP IgG1. These results indicate that BP IgG2 and IgG4 have a capability to inhibit the increase of [Ca2+]i induced by BP IgG1.

Blister fluid for the diagnosis of subepidermal immunobullous diseases: a comparative study of basement membrane zone autoantibodies detected in blister fluid and serum

The subepidermal immunobullous diseases bullous pemphigoid (BP), cicatricial pemphigoid (CP), pemphigoid gestationis (PG) and linear IgA disease (LAD) are characterized by circulating and in vivo deposition of antibodies to antigens in the cutaneous basement membrane zone (BMZ). Indirect immunofluorescence (IMF) of serum is a routine diagnostic test to detect circulating BMZ antibodies in these diseases. We have compared the titres of IgG and IgA and their subclasses, also of IgM and IgE BMZ antibodies in serum and aspirated blister fluid in 35 adult patients with subepidermal immunobullous diseases: BP (n = 30), PG (n = 2), CP (n = 1), and LAD (n = 2), by indirect IMF on intact and salt-split skin. The antibody titre in blister fluid was the same or one dilution less than serum in most cases and there was no significant difference between these results (P > 0.05). IgG1 and IgG4 were the predominant subclasses in both blister fluid and serum in BP. Indirect IMF of serum and blister fluid was also carried out on trypsinized epidermal cells in a subgroup of patients with BP (n = 19). Typical polar fluorescence was obtained in all 14 cases which had positive indirect IMF on intact and split skin. Our findings demonstrate that blister fluid can be used as an alternative to serum for indirect IMF in subepidermal immunobullous diseases. This avoids the need for venesection and has a practical application in children and those with poor venous access.

IgE antibodies in sera from patients with bullous pemphigoid are autoantibodies preferentially directed against the 230-kDa epidermal antigen (BP230)

Bullous pemphigoid (BP) is unique among autoimmune skin diseases in which a high serum IgE level has been detected. We sought to determine the antigenic specificity of these IgE antibodies in 39 BP sera by immunofluorescence microscopy, immunoblot, and ELISA. The patient's sera contained IgG antibodies to 230-kDa (BP230) (n = 20), 180-kDa (BP180) (n = 9), and both BP230 and BP180 (n = 10) antigens. Serum IgE levels varied from 29 to 5000 kIU/L (mean +/- SD, 856 +/- 1426 kIU/L), among which sera containing IgG antibodies to BP230 had an IgE level on average 4.3 times higher than anti-BP180 sera. IgE antibodies in 18 sera were found to be autoantibodies reactive either with an epidermal component of basement membrane zone by immunofluorescence microscopy on 1 M NaCl-split skin or with a 230-kDa antigen by immunoblots of cultured human keratinocytes. The 230-kDa epidermal antigen recognized by IgE antibodies comigrated with the BP230 as labeled by a specific human monoclonal antibody. IgE anti-BP230 antibodies in patients' sera were always associated with IgG autoantibodies. No sera contained IgE antibodies to BP180 or to any other epidermal or dermal antigens as verified by immunoblot and ELISA. A good correlation was found between the presence of IgE circulating autoantibodies and the level of serum IgE (P < 0.004). IgE antibodies to BP230, like IgG autoantibodies, were mapped primarily to the C-terminal end of the protein, as they labeled rBP55, a BP230 recombinant protein encoded by a cDNA for the C-terminal end of BP230.

IgG subclasses of canine anti-erythrocyte, antinuclear and anti-thyroglobulin autoantibodies

A panel of monoclonal antibodies (mAbs) reactive with the four canine IgG subclasses (IgG1, IgG2, IgG3 and IgG4) was used to investigate the activity of IgG subclasses in autoimmune responses to erythrocytes, nuclear antigens and thyroglobulin in dogs with autoimmune disease. mAbs specific for canine IgG1 and IgG4 were able to agglutinate normal dog erythrocytes coated with purified canine IgG containing each of the four subclasses. IgG1 autoantibodies were demonstrated on the surface of erythrocytes from seven dogs with Coombs'-positive autoimmune haemolytic anaemia and IgG4 autoantibodies were also present in two of these cases. Serum antinuclear antibody was shown in nine dogs to be predominantly of IgG1, IgG3 and IgG4 subclasses with only one of the dogs also producing an IgG2 antinuclear antibody. The IgG subclass profile of antinuclear antibodies differed between dogs with polyarthritis and dogs with other systemic disease. In six dogs with hypothyroidism, thyroglobulin autoantibodies of subclasses, IgG1, IgG2 and IgG4 predominated, but one dog also produced significant levels of IgG3 thyroglobulin autoantibodies. The mAbs are widely applicable to the study of the pathogenesis of canine autoimmune disease.

Significance of IgG-subclass antibody determinations in bullous pemphigoid

The presence of circulating basement membrane zone (BMZ) antibodies is characteristic of patients with bullous pemphigoid (BP) and are routinely employed in making the diagnosis. The positive tests, however, occur in 50-70% of patients with BP, thus necessitating consideration of other tests in a significant number of patients. The purpose of this study was to examine the efficacy of indirect immunofluorescence (IF) tests specific for various IgG subclasses antibodies to BMZ in BP, especially in patients who are seronegative on routine indirect IF tests with fluorescein-conjugated antibodies to IgG. BMZ antibodies primarily are of IgG4 subclass and are present in all BMZ antibody positive BP cases. Of BP patients negative for BMZ antibodies, 72% were found positive when tested for IgG4 subclass antibodies. In conclusion, testing for IgG4 subclass BMZ antibodies enhances the sensitivity of serum tests from 68.5% to 91%. This may be due in part to the inherent increased sensitivity of the assay and for detecting subclasses of IgG and in part, due to the subclass distribution of the BP antibodies.

Serum levels of soluble CD23 in patients with bullous pemphigoid

In this study, we tested the serum levels of soluble CD23 (sCD23) in 27 bullous pemphigoid (BP) patients and compared them with the disease activity. Soluble CD23 is the cleaved portion of the low affinity Fc receptor for IgE (Fc epsilon RII/CD23) which has an affinity for IgE and regulates IgE synthesis. Although bullous pemphigoid (BP) is a subepidermal blistering disease characterized by IgG class autoantibodies against the basement membrane of stratified squamous epithelia, several IgE-related phenomena have been reported. Recently, we have shown that Fc epsilon RII-expressing and IgE-bearing cells are detectable in the lesional skin and concluded that an IgE-Fc epsilon RII/CD23 system may be involved in the pathogenesis of this disease. The serum level of sCD23 in BP patients was significantly higher than healthy controls (p < 0.01). In 11 out of 12 patients, the alteration of serum sCD23 levels correlated well with the disease activity. Thus the serum level of sCD23 is useful as a new parameter for assessing the level of disease activity in BP. High levels of sCD23 may represent part of an IgE-mediated immune reaction which may play a role in the pathogenesis of BP.

Tissue immunoglobulin G subclasses observed in immune-mediated dermatopathy, deep pyoderma and hypersensitivity dermatitis in dogs

A panel of monoclonal antibodies has been used to define three of the four subclasses of canine immunoglobulin G (IgG2, IgG3 and IgG4) in formalin-fixed tissues. These reagents, together with a polyclonal antiserum specific for the Fc region of canine IgG, were used in an immunohistochemical study of biopsies of skin from five normal dogs and from the lesions of canine pemphigus foliaceus in seven dogs, discoid lupus erythematosus in eight dogs, bullous pemphigoid in one dog, cutaneous drug eruption in two dogs, deep pyoderma in 13 dogs and hypersensitivity dermatitis in eight dogs. IgG autoantibody was identified in the skin of all the dogs with immune-mediated dermatoses by using the polyclonal reagent, and antibody of the IgG2 and/or IgG4 subclass was identified in the epidermis of three of the dogs with pemphigus foliaceus, two of those with discoid lupus erythematosus and in the dog with bullous pemphigoid. In all the lesions, the infiltrate of dermal plasma cells consisted of similar numbers of IgG2 and IgG4 bearing cells, with relatively few IgG3 positive cells. The total number of these cells was generally approximately the same as or greater than the number of cells labelled with the polyclonal reagent. There was no significant difference between the IgG-bearing plasma cell infiltrate in German shepherd dogs with deep pyoderma and that in dogs of other breeds. The infiltration of IgG2 and IgG4 bearing plasma cells into the skin of dogs with a range of cutaneous disorders was related to the selectively enhanced serum levels of these subclasses in the diseased dogs.

Relationship between antigens and IgG subclasses in bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized in part by the presence of tissue-bound and circulating antibodies (mostly of IgG) to the basement membrane zone (BMZ). We previously reported that IgG subclasses of BP antibodies were IgG1, IgG2 and IgG4, and that only BP IgG1 fixed complements. In this study, we examined whether BP IgG sub-classes bound to the same epitope of BP antigen or a different epitope. In an inhibition immunofluorescence studies, the complement fixing capability of IgG1 was inhibited by the pretreatment with IgG4 and partially inhibited by IgG2. On immunoblot analysis, IgG1 and IgG4 were bound to the same MW of BP antigen. In enzyme-linked immunosorbent assay (ELISA), the binding capability of IgG subclass fractions from patients with BP to synthetic peptide P1-2, exceeding normal IgG subclass fractions was seen in five IgG1, one IgG2 and two IgG4, from eight BP patients. The binding capability of IgG subclass fractions from the patients with BP to P1-1, exceeding the normal IgG fractions was seen in two IgG1, three IgG2 and one IgG4 from ten BP patients. On inhibition ELISA, the binding activity to P1-2 of IgG4 was partially inhibited by the pretreatment of IgG1 and IgG2. These findings suggest that BP IgG1, IgG2 and IgG4 could bind to the same epitope though considerable variation occurred between patients.

IgE and its related phenomena in bullous pemphigoid

This study was designed to analyse IgE and its related phenomena in bullous pemphigoid (BP). We analysed 17 BP sera by indirect immunofluorescence (IIF) and immunoblotting (IB) using a monoclonal antibody to IgE. In addition, inflammatory cells in lesional skin from 11 patients with BP were analysed by the alkaline phosphatase-anti-alkaline phosphatase (APAAP) technique using monoclonal antibodies to IgE and Fc epsilon RII/CD23. IgE class anti-basement membrane zone (BMZ) autoantibody was detected in nine of 17 sera (52.9%) by IIF. IgG class anti-BMZ antibody could block the BMZ-binding reactivity of IgE class antibody. Titres of IgE class autoantibody in the sera ranged from 1:40 to 1:320, and statistically correlated with serum IgE levels. Two of 11 sera contained an IgE class autoantibody which recognized a 230-kDa BP antigen by IB. By radio-allergosorbent test (RAST), IgE-specific antibodies to an extended series of common inhalant and food allergens were detectable in six sera with high concentrations of total IgE (over 3,300 IU/ml). IgE-bearing and Fc epsilon RII-expressing cells were demonstrated in the upper dermis and along the BMZ in seven of 11 biopsy specimens by the APAAP technique. The distribution and number of IgE-bearing cells in the lesions were similar to those of the Fc epsilon RII-expressing cells. These results suggest that both IgE-mediated immune responses and autoimmunity characterize BP as distinctive features.