Capability of complement fixation of pemphigus antibodies in vitro

Sparking Fire Under the Skin? Answers From the Association of Complement Genes With Pemphigus Foliaceus

Skin blisters of pemphigus foliaceus (PF) present concomitant deposition of autoantibodies and components of the complement system (CS), whose gene polymorphisms are associated with susceptibility to different autoimmune diseases. To investigate these in PF, we evaluated 992 single-nucleotide polymorphisms (SNPs) of 44 CS genes, genotyped through microarray hybridization in 229 PF patients and 194 controls. After excluding SNPs with minor allele frequency <1%, out of Hardy-Weinberg equilibrium in controls or in strong linkage disequilibrium (r2 ≥ 0.8), 201 SNPs remained for logistic regression. Polymorphisms of 11 genes were associated with PF. MASP1 encodes a crucial serine protease of the lectin pathway (rs13094773: OR = 0.5, p = 0.0316; rs850309: OR = 0.23, p = 0.03; rs3864098: OR = 1.53, p = 0.0383; rs698104: OR = 1.52, p = 0.0424; rs72549154: OR = 0.55, p = 0.0453). C9 (rs187875: OR = 1.46, p = 0.0189; rs700218: OR = 0.12, p = 0.0471) and C8A (rs11206934: OR = 4.02, p = 0.0323) encode proteins of the membrane attack complex (MAC) and C5AR1 (rs10404456: OR = 1.43, p = 0.0155), a potent anaphylatoxin-receptor. Two encode complement regulators: MAC-blocking CD59 (rs1047581: OR = 0.62, p = 0.0152) and alternative pathway-blocking CFH (rs34388368: OR = 2.57, p = 0.0195). One encodes opsonin: C3 (rs4807895: OR = 2.52, p = 0.0239), whereas four encode receptors for C3 fragments: CR1 (haplotype with rs6656401: OR = 1.37, p = 0.0382), CR2 (rs2182911: OR = 0.23, p = 0.0263), ITGAM (CR3, rs12928810: OR = 0.66, p = 0.0435), and ITGAX (CR4, rs11574637: OR = 0.63, p = 0.0056). Associations reinforced former findings, regarding differential gene expression, serum levels, C3, and MAC deposition on lesions. Deregulation of previously barely noticed processes, e.g., the lectin and alternative pathways and opsonization-mediated phagocytosis, also modulate PF susceptibility. The results open new crucial avenues for understanding disease etiology and may improve PF treatment through additional therapeutic targets.

Immunohistochemical analysis of the distribution of desmoglein 1 and 2 in the skin of dogs and cats

OBJECTIVE

To compare the distribution of desmoglein (Dsg) 1 and 2 in skin specimens obtained from dogs and cats to provide information about the possible role of the density of Dsg 1 and 2 in the localization of lesions attributable to pemphigus foliaceus in these 2 species.

SAMPLE POPULATION

Skin biopsy specimens obtained from 4 dogs and 4 cats.

PROCEDURE

Biopsy specimens were collected from the muzzle, bridge of the nose, ear, dorsum, abdomen, area adjacent to the teats, and footpads of each animal. Immunohistochemical analysis was performed on formalin-fixed, paraffin-embedded skin samples by use of a biotinylated mouse monoclonal anti-Dsg 1 and 2 antibody raised against bovine muzzle. Color development was performed by use of the streptavidin-biotin-peroxidase method with a chromogenic substrate.

RESULTS

Immunohistochemical staining yielded a positive reaction in skin samples obtained from all anatomic sites. The intensity and distribution of staining were related to the number of layers of the stratum spinosum. No differences were detected between samples obtained from dogs and cats.

CONCLUSIONS AND CLINICAL RELEVANCE

No differences in intensity of Dsg 1 and 2 antigen were observed in the stratum spinosum between skin samples obtained from dogs and cats. Analysis of this result suggests that factors other than the distribution of Dsg may be responsible for the differences in localization of primary clinical lesions in dogs and cats with pemphigus foliaceus.

In vitro C3 mRNA expression in Pemphigus vulgaris: complement activation is increased by IL-1alpha and TNF-alpha

BACKGROUND

Pemphigus vulgaris (PV) is a potentially life-threatening disease, characterized immunohistologically by IgG deposits and complement activation on the surface of keratinocytes. Complement activation has been implicated in the pathogenesis with C3 deposits in about 90% of patients.

OBJECTIVE

In order to further elucidate the role of complement in PV and to define which cytokines play a role in C3 mRNA expression, we performed an in vitro study in human keratinocytes.

METHODS

Normal human epidermal keratinocytes (NHuK) were incubated with PV serum and C3 mRNA was measured. We previously had shown that IL-1alpha and TNF-alpha are expressed in PV in vivo and in vitro. Since cytokines are able to modulate complement activation, mRNA expression was evaluated in a similar experiment after pretreatment using antibodies against IL-1alpha and TNF-alpha.

RESULTS

Incubation of NHuK with PV sera caused their detachment from the plates after 20-30 minutes with a complete acantholysis within 12 hours. An early C3 mRNA expression was seen after 30 minutes with a peak level after 1 hour. Blocking studies, using antibodies against human IL-1alpha and TNF-alpha in NHuK together with PV-IgG, showed reduction of in vitro induced acantholysis and inhibition of C3 mRNA expression.

CONCLUSION

This study supports the hypothesis that complement C3 is important in PV acantholysis and that complement activation is increased by IL-1alpha and TNF-alpha.

Circulating pemphigus IgG in families of patients with pemphigus: comparison of indirect immunofluorescence, direct immunofluorescence, and immunoblotting

BACKGROUND

Patients with pemphigus vulgaris (PV) are genetically linked to two alleles of the HLA subgroup, and circulating antibodies were found in first-degree relatives of these patients, thus showing genetic predisposition.

OBJECTIVE

Our purpose was to determine the occurrence of circulating true PV-IgG in patients' relatives.

METHODS

Circulating PV-IgG was determined in 21 first-degree relatives of 12 patients with PV by indirect immunofluorescence on monkey esophagus, carcinoma A431 cultures, and Western immunoblotting. Direct immunofluorescence was performed on skin biopsy specimens of 20 relatives.

RESULTS

Circulating PV-IgG was detected in 15 relatives (71%) by all methods tested. Good correlation was found between immunoblot reactivity and immunofluorescence. Of the 15 "positive" relatives, only five showed fixation of IgG to epidermal cells in vivo.

CONCLUSION

The permeability of the epidermis or epidermal cell reactivity in vivo probably controls the expression of disease in patients' relatives.

Autoantibodies against the amino-terminal cadherin-like binding domain of pemphigus vulgaris antigen are pathogenic

Complementary DNA cloning of the 130-kD pemphigus vulgaris (PV) autoantigen (PVA) has indicated that it is a member of the cadherin family of Ca(2+)-dependent cell adhesion molecules. By homology with typical cadherins, PVA has five extracellular domains (EC1 through EC5). To localize immunogenic domains and to determine whether antibodies against them might be pathogenic, we produced beta-galactosidase fusion proteins with cDNA encoding different portions of the extracellular domains of PVA (EC1-2, EC3-5, and each individual domain). Immunoblot analysis of these fusion proteins with 23 PV patients' sera demonstrated that major immunogenic regions of PVA are located on the EC1, EC2, and EC4 domains. IgG was affinity-purified from PV sera on fusion proteins representing the amino (EC1-2) and carboxy (EC3-5) terminus of the extracellular PVA, and injected into neonatal mice. PV IgG affinity-purified on the EC1-2 fusion protein caused suprabasilar acantholysis, the typical histological finding of PV, but IgG affinity-purified on the EC3-5 fusion protein or beta-galactosidase alone did not. These results indicate that at least one pathogenic epitope, which is sufficient to cause suprabasilar acantholysis in neonatal mice, is located on the amino-terminal region of PVA, an area thought to be important in cadherin homophilic adhesion.

IgG subclasses of intercellular and basement membrane zone antibodies: the relationship to the capability of complement fixation

There are four main subclasses of human IgG: IgG1, IgG2, IgG3, and IgG4, among which IgG1-IgG3 activate complement, but IgG4 does not. We studied the IgG subclasses of anti-intercellular (IC) antibodies in pemphigus patients and anti-basement membrane zone (BMZ) antibodies in bullous pemphigoid (BP) patients by immunofluorescent staining using mouse monoclonal antibodies against human IgG1-IgG4. At the same time, the capability of complement fixation of each serum was determined by means of complement immunofluorescence. In both pemphigus and BP autoantibodies, various distributions of IgG subclass were shown, but specific patterns were not observed. In BP, all of the complement fixing antibodies had at least one of IgG1-IgG3 subclasses, while noncomplement fixing antibodies only possessed IgG4. This result agreed well with the biologic characteristics of IgG subclasses in respect of complement fixing capability. On the contrary, in pemphigus, the circulating antibodies showed a distribution of IgG subclass which did not correlate with the biologic characteristics in terms of complement activation. This discrepancy may further dispute the roles of the complement system on the bulla formation in pemphigus.

Comparison of IgG subclasses and complement binding activity of autoantibodies from patients with bullous pemphigoid and pemphigus

Bullous pemphigoid and pemphigus are autoimmune disorders of skin of unknown etiology and are characterized by the presence of immunoreactants in the skin and circulating autoantibodies to skin components. The distribution of IgG subclass antibodies to intercellular substance (ICS) of pemphigus and basement membrane zone substance (BMZ) of bullous pemphigoid was analyzed by using monoclonal antibodies to human IgG subclasses. IgG4 type anti-BMZ antibody was found in the majority of patients with bullous pemphigoid (88% in skin and 96% in serum). One third to one half of bullous pemphigoid patients had IgG1 and IgG2 anti-BMZ antibodies. The majority of bullous pemphigoid skin (92%) had complement in skin, however only one third of their sera had complement binding activity in vitro. IgG1 anti-ICS antibody was the predominant one in patients with pemphigus (86% in skin and 80% in circulation). IgG4 anti-ICS antibody was seen in two thirds of specimens from pemphigus patients. IgG3 subclass antibody was more frequently seen in pemphigus than in bullous pemphigoid patients. Two-thirds of pemphigus sera were capable of activating complement in vitro. The complement binding activity was directly associated with IgG1 and/or IgG3 subclass antibodies. The possible mechanisms for the restricted IgG4 subclass antibodies in bullous pemphigoid and pemphigus are discussed.

IgG subclasses of intercellular antibodies in Brazilian pemphigus foliaceus--the relationship to complement fixing capability

Human IgG possesses four main subclasses, namely IgG1, IgG2, IgG3, and IgG4, of these IgG1-IgG3 fix complement, but IgG4 does not. We have studied the IgG subclasses of intercellular antibodies in the sera from 20 patients with Brazilian pemphigus foliaceus by immunofluorescent staining using mouse monoclonal antibodies against human IgG1-IgG4. At the same time, the complement fixing capability of each antibody was examined by complement immunofluorescence. All of four subclasses were frequently detected in most cases with varying distributions. However, no specific pattern was observed. Complement fixing antibodies were found in four patients. However, the distribution of IgG subclasses was incompatible with their known characteristics in terms of complement activation. This discrepancy increases the controversy over the importance of the complement system in blister formation in pemphigus.

Complement fixation by pemphigus antibody. V. Assembly of the membrane attack complex on cultured human keratinocytes

Previous studies have shown that pemphigus vulgaris (PV) IgG will fix early complement components (C1q, C4, and C3) to cultured murine epidermal cell surfaces and that PV IgG and complement alter epidermal cell membrane integrity. The present study was undertaken to determine if assembly of terminal complement components (C5, C6, C7, C8, and C9) and expression of C5b-9 neoantigens occur when PV IgG interacts with human keratinocyte (HuK) cell surface antigens in the presence of a source of complement. Monoclonal antibodies specific for C5, C6, C7, C8, C9, and C5b-9 neoantigens were screened for reactivity to the individual complement components in an assembled complex of human C5b-9 on rabbit red blood cell ghosts. Monoclonal antibodies (tissue culture supernatants) that bound to antigenic determinants accessible in the C5b-9 complex were selected for this study using immunofluorescence methods. HuK treated with PV IgG fixed C5, C6, C7, C8, C9, and C5b-9 neoantigens in a characteristic speckled pattern, while normal IgG did not. Heat inactivation or EDTA treatment of the complement source, or substitution of C2-depleted serum abolished C5, C6, C7, C8, C9, and C5b-9 neoantigen staining. PV IgG and complement also resulted in significant cytotoxicity to cell membranes as assessed using an ethidium bromide-fluorescein diacetate assay. These results suggest that PV IgG will activate the membrane attack complex of the complement system on HuK cell surfaces, resulting in cytotoxicity to cell membranes, further implicating complement in the pathogenesis of pemphigus.

Subclass distribution of human IgG autoantibodies in pemphigus

The distribution of IgG subclasses in the intercellular substance (ICS) reactive autoantibodies in serum of 10 patients with pemphigus was analyzed by semiquantitative indirect immunofluorescence (IF) using the HP series of monoclonal antibodies specific for the four human IgG subclasses. IgG4 ICS specific autoantibody was present in all 10 sera at a titer of 10 to 320, while IgG1 antibodies were found in 9 of 10 sera at a seemingly lower level. IgG3 autoantibodies were detected in the serum of one patient, only after isolation of IgG using ion-exchange chromatography. Autoantibodies of IgG subclass 2 were not detectable in any of the 10 sera tested. One of the ten patients displayed circulating anti-ICS antibodies of only the IgG4 isotype.

Monoclonal antibody to a 35 kD epidermal protein induces cell detachment

A murine monoclonal antibody (ECS-1) was prepared from BALB/c mice immunized with trypsinized cultured human foreskin keratinocytes. The antibody showed a pattern suggestive of intercellular staining on the nucleated layers of normal human epidermis, adult palm, mouse lip epidermis, and cultured human keratinocytes. ECS-1 stained human fetal skin by 9 weeks estimated gestational age. ECS-1 reacted with a 35 kD protein extracted from neonatal foreskin epidermis and cultured human keratinocytes. The protein required Nonidet P-40 or sodium dodecyl sulfate and mercaptoethanol for solubilization. ECS-1 induced epidermal cell detachment which was enhanced by complement. ECS-1 shares characteristics with human pemphigus antibodies.

Complement fixation by pemphigus antibody. III. Altered epidermal cell membrane integrity mediated by pemphigus antibody and complement

The present study investigates the effects of pemphigus IgG and complement upon cell viability and/or membrane integrity using trypan blue exclusion, ethidium bromide (EB) staining, and fluorescein diacetate (FDA) conversion by living cells. Forty-eight-hour cultivated epidermal monolayers of neonatal BALB/c mice were incubated in media containing 1 mg/ml purified pemphigus IgG for 48 h in either the presence or absence of complement (absorbed AB sera). Adherent and detached cells were examined by both phase and fluorescence microscopy. Results from trypan blue exclusion showed that pemphigus IgG plus complement produced a modest decrease in exclusion of the dye compared to pemphigus IgG without complement. When FDA/EB comparisons were made, however, the differences were more substantial. When complement plus pemphigus IgG was added to cultures, the number of FDA-positive adherent cells decreased significantly and the number of EB-positive detached cells increased significantly. The effects of complement were inhibited by the use of heat-inactivated AB sera or by C1q depletion of AB sera. No significant effect on the cells was observed in the presence or absence of complement when pemphigus F(ab')2 fragments or when normal IgG was used. Plasminogen depletion of the complement source did not interfere with complement and pemphigus IgG effects as judged by the FDA/EB assay. These studies suggest that pemphigus antibody in the presence of complement alters cell membrane integrity and supports the contention that complement may play a significant role in the mechanism of acantholysis.

Immunopathologic mechanisms in pemphigus and bullous pemphigoid

Pemphigus and bullous pemphigoid are autoimmune bullous diseases of the skin. Pemphigus, an intraepidermal blistering disease, is characterized by autoantibodies reactive with antigens located in the intercellular spaces or on the surfaces of epidermal cells. These antibodies, which have recently been shown to activate complement, appear to be the cause of the basic pathologic process of pemphigus, acantholysis. The complement system and the plasminogen-plasmin system may be important mediators in the detachment of epidermal cells. Bullous pemphigoid, a subepidermal blistering disease, is characterized by autoantibodies reactive with an antigen located in the lamina lucida region of the basement membrane zone. These autoantibodies, which will avidly fix complement, appear to mediate subepidermal separation by attraction of a variety of inflammatory cells. Anaphylatoxins, released by activation of C4 and C3, or specific IgE antibodies, may activate mast cells with release of ECF-A attracting eosinophils. With activation of C5, C5a is released which could attract polymorphonuclear leukocytes. Antigen-specific lymphocytes, which can also contribute histamine releasing substances, may also be involved. The exact mechanism by which the epidermis separates from the dermis in bullous pemphigoid, however, remains unresolved.

Complement fixation by pemphigus antibody. I. In vitro fixation to organ and tissue culture skin

Although complement is often detected in the intercellular substance of pemphigus skin lesions, the ability of pemphigus antibodies to fix complement in vitro is controversial. The purpose of this study was to test in vitro complement fixation abilities of pemphigus antibodies further using organ and tissue culture methods. Epidermal cell monolayers from mouse tail were incubated with the purified IgG fraction of pemphigus serum followed by purified Clq. Binding of Clq, as well as IgG was demonstrated by immunofluorescence methods. When purified Clq was replaced with normal human serum as a complement source, positive C3 and C4 staining were also evident. When purified IgG of normal human serum was used in place of pemphigus IgG, similar immunofluorescence staining was not observed. Further evidence for complement fixation in vitro by pemphigus antibodies was obtained using organ cultures. Organ culture of normal human skin and monkey esophageal mucosa cultured in purified pemphigus IgG showed intercellular substance binding of IgG. No binding was observed when normal IgG was substituted for pemphigus IgG. Additional organ culture sections were then treated with complement (fresh normal human serum) and tested by in vitro complement staining. Fixation of Clq, C4, and C3 was noted in intercellular substance areas of organ cultured skin and mucosa incubated with pemphigus IgG but not those incubated with normal IgG. Prior treatment of pemphigus IgG organ cultured skin sections with unlabeled anti-C3, blocked positive C3 staining. These results suggest that some pemphigus antibodies are capable of activating complement in vitro.

An immunofluorescence complement-fixation test for detection of human papilloma viruses in various warts and wartlike lesions of epidermodysplasia verruciformis

Comparative studies of indirect immunofluorescence (IF) and IF complement fixation tests were performed in 11 warts induced by various human papilloma viruses (HPV) or wartlike lesions of epidermodysplasia verruciformis. For the detection of HPVs, specific immune sera against HPV1, HPV2, HPV3, HPV5, HPV9 and/or HPV8 were used. The complement-fixation test proved to be as specific as the indirect IF method for the detection of HPVs in the tissues and was superior in clarity of IF readings (no nonspecific IF staining).

In vitro complement activation by intercellular antibodies

By in vitro complement immunofluorescence, 6 sera from pemphigus with intercellular antibodies were tested for their capability to fix C1q, C4, C3, and properdin. All 6 serum samples yielded positive reaction for C3 staining. Three serum samples gave positive staining for C1q, 5 serum samples for C4, and 3 serum samples for properdin, respectively. Substitution of C2 deficient serum as a complement source inhibited C3 and properdin staining but not positive C1q and C4 staining. These results are best explained by the concept that complement activation in vitro by intercellular antibodies occurs via the classical pathway followed by assembly of the C3 amplification mechanism.

Mechanism of lesion production in pemphigus and pemphigoid

Current evidence strongly supports the theory that the lesions of pemphigus are due to binding of pemphigus antibody to an antigen in or near the epidermal cell membrane, which causes a release of at least one enzyme which results in dissolution of the intercellular attachments and acantholysis. Similarly, strong evidence supports the hypothesis that pemphigoid blisters are due to binding of antibody at the basement membrane, followed by activation of complement and release of anaphylatoxins which activate tissue mast cells to release eosinophil chemotactic factor. These eosinophils then release tissue-destructive enzymes and reactive oxygen intermediates directly onto the basement membrane zone, with loss of dermoepidermal adherence and formation of blisters.

Experimental acantholysis by complement-fixing intercellular antibodies

Complement-fixing intercellular antibodies were detected in 10 of 17 sera from untreated pemphigus patients. The role of complement in the organ culture system was investigated using these sera. Ten sera possessing complement-fixing intercellular antibodies showed IgG binding to the intercellular substance in the organ-cultured skin and acantholysis-like changes were observed in eight cases. C3 deposition was not seen in any case. However, after treatment of the sections of cultured skin with fresh normal human serum, complement fixation of the intercellular substance by bound IgG was revealed in all the ten cases. No significant differences in the grade of acantholysis-like changes between the complement-depleted system and the complement-supplied system were observed. Complement does not appear to be necessary in the acantholytic process in the in vitro organ culture system, even though we considered the presence of complement-fixing intercellular antibodies.

Binding of bullous pemphigoid antibodies to basal cells

Eight out of 12 serum samples from patients with bullous pemphigoid having basement membrane zone antibodies gave positive binding not only to the basement membrane zone but also to the basal cell membrane and/or cytoplasm as observed by complement immunofluorescence. Reaction of fluorescein labeled pemphigus vulgaris gamma-globulins, binding mainly to the lower intercellular spaces of the epidermis, was greatly reduced by the prior incubation of high-titered bullous pemphigoid sera having the reactivity to the basal cells, while that of fluorescein labeled pemphigus foliaceus gamma-globulins binding mainly to the upper and middle intercellular spaces, was not influenced by the prior application of these bullous pemphigoid sera. These results indicate that bullous pemphigoid antibodies are heterogenous and can be classified into 2 types and that some cross reaction is present between pemphigus antibodies and bullous pemphigoid antibodies having the reactivity to the basal cells.