In vitro complement activation by intercellular antibodies

The role of subclass switching in the pathogenesis of endemic pemphigus foliaceus

Endemic pemphigus foliaceus, like the sporadic form seen in the developed world, is mediated by IgG antibodies to desmoglein-1. We studied an endemic focus in Limao Verde, Brazil, where disease prevalence is 3.4%. We previously detected IgG antibodies to desmoglein-1 in 97% of patients, but also in 55% of normal subjects in the endemic focus, with progressively lower levels in normal subjects in surrounding areas. An environmental trigger is hypothesized to explain these and other findings. In this study we sought to determine if patients and enzyme-linked-immunosorbent-assay-positive normal subjects in Limao Verde differ in IgG subclass response to desmoglein-1. We developed a sensitive and specific subclass enzyme-linked immunosorbent assay using recombinant desmoglein-1 and standardized the assay to enable comparability between the four subclasses. We found that normal subjects have an IgG1 and IgG4 response, whereas patients have similar levels of IgG1 but a mean 19.3-fold higher IgG4 response. Patients in remission have a weak IgG4 response, and a 74.3-fold higher IgG4 response is associated with active disease. Finally, in five patients in whom we had blood samples from both before and after the onset of clinical disease, a mean 103.08-fold rise in IgG4 was associated with onset of clinical disease, but only a mean 3.45-fold rise in IgG1. These results suggest that the early antibody response in normal subjects living in the endemic area and in patients before the onset of clinical disease is mainly IgG1. Acquisition of an IgG4 response is a key step in the development of clinical disease.

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.

Mucocutaneous features of autoimmune blistering diseases

This review will describe adult onset mucocutaneous/autoimmune diseases that involve defects in cell-to-cell, cell-to-matrix, or cell-to-basement membrane adhesion. Included in this group are pemphigus, cicatricial pemphigoid, linear IgA bullous dermatosis, epidermolysis bullosa acquisita, and bullous systemic lupus erythematous. Detection and treatment of blistering disorders that manifest early in the oral cavity may prevent widespread involvement of skin. During the past few years, targets of autoantibodies have been clarified and new targets have been identified, allowing better understanding of the pathophysiology involved in these diseases. New information about more effective regimens with fewer side effects has also been obtained, presenting new treatment options. Clinical manifestations and management of these disorders will be described as well as histopathologic, ultrastructural, and immunopathologic studies that distinguish each disorder and facilitate diagnosis and treatment.

The role of complement-derived mediators in inflammatory skin diseases

The complement system represents an important nonspecific skin defense mechanism. Its activation leads to the generation of products that not only help to maintain normal host defenses but also mediate inflammation and tissue injury. Proinflammatory products of complement include large fragments of C3 with opsonic and cell-stimulatory activities (C3b and C3bi), low molecular weight anaphylatoxins (C3a, C4a, and C5a), and membrane attack complex. Among them C5a or its degradation product C5a des Arg seems to be the most important mediator because it exerts a potent chemotactic effect on inflammatory cells. Intradermal administration of C5a anaphylatoxin induces skin changes quite similar to those observed in cutaneous hypersensitivity vasculitis that occurs through immune complex-mediated complement activation. Complement activation is involved in the pathogenesis of the inflammatory changes in autoimmune bullous dermatoses. In pemphigus complement activation by pemphigus antibody in the epidermis seems to be responsible for the development of characteristic inflammatory changes termed eosinophilic spongiosis. In bullous pemphigoid (BP) interaction of basement membrane zone antigen and BP antibody leads to complement activation that seems to be related to leukocytes lining the dermoepidermal junction. Resultant anaphylatoxins not only activate the infiltrating leukocytes but also induce mast cell degranulation which facilitates dermoepidermal separation and eosinophil infiltration. Similar complement activation seems to play a more direct role in the dermoepidermal separation noted in epidermolysis bullosa acquisita and herpes gestationis. Anaphylatoxin generation via the alternative pathway activation under light irradiation is implicated in the development of the immediate erythematous phototoxic reactions induced by such well-known chemicals as porphyrin, chlorothiazide, demethylchlortetracycline, and chlorpromazine.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Complement activation in Brazilian pemphigus foliaceus

Brazilian pemphigus foliaceus is an autoimmune blistering skin disease of man that has a very high incidence in a confined geographical distribution. Rocket immunoelectrophoresis of plasma showed increased levels of complement fragments, C4d and Ba, indicating activation of complement through both the classical and the alternative pathways. Less sensitive methods such as CH50, total C3 and C4 did not demonstrate this activation, and immune complex measurements were within normal range. While complement may not be absolutely necessary for the development of skin lesions, our longitudinal studies show that activation of complement is at its highest during the most active phase of the disease.

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.

Decay-accelerating factor in human skin is associated with elastic fibers

Recently a complement inhibitor, decay-accelerating factor (DAF), has been found in association with uncharacterized fibers in the extracellular matrix of human dermis. Here we show by immunohistochemistry and immunoelectronmicroscopy that DAF is on the periphery of elastic fibers, and that it appears to be associated with some microfibrillar elements that cover the fibers. That DAF is a component of these microfibrils is also suggested by studies of lesional skin from anetoderma, a disease characterized by destruction of elastic fibers. In two patients we found a network of residual fine fibers in the dermis that stain with antibodies against DAF and fibrillin (one of the proteins known to be present in the microfibrils of elastin), but do not stain with antibodies to elastin. Western blot analysis of dermal extracts with monoclonal antibodies to DAF identified a 67 kDa molecule, slightly smaller than membrane DAF, and similar in size to soluble DAF found in secretions. It is possible that together with vitronectin, an inhibitor of the membrane attack complex recently identified in association with elastin, DAF prevents damage of elastic fibers by complement.

Pemphigus

The term pemphigus refers to a group of autoimmune intraepidermal blistering diseases of the skin and mucous membranes. Several clinical variants of pemphigus are recognized. The major histologic feature of all variants is acantholysis, the disruption of normal cell-to-cell adhesion, which leads to intraepidermal blister formation. Most patients with pemphigus demonstrate IgG autoantibodies directed against an antigen located on the surface of keratinocytes. Although the stimulus for autoantibody production is unknown, several mechanisms have been proposed to explain the pathogenesis of acantholysis. One popular model proposes that pemphigus antibodies induce acantholysis through local stimulation of the plasminogen-plasmin system. Another model proposes that pemphigus antibodies fix complement and thereby alter cell membrane integrity to produce acantholysis. Prior to the availability of corticosteroids, pemphigus vulgaris was commonly fatal. Treatment with glucocorticosteroids has drastically improved the prognosis. Immunosuppressive agents and plasmapheresis have been used successfully in some patients with severe disease.

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.