The complement system in pemphigus, bullous pemphigoid and herpes gestationis

The relevance of complement in pemphigoid diseases: A critical appraisal

Pemphigoid diseases are autoimmune chronic inflammatory skin diseases, which are characterized by blistering of the skin and/or mucous membranes, and circulating and tissue-bound autoantibodies. The well-established pathomechanisms comprise autoantibodies targeting various structural proteins located at the dermal-epidermal junction, leading to complement factor binding and activation. Several effector cells are thus attracted and activated, which in turn inflict characteristic tissue damage and subepidermal blistering. Moreover, the detection of linear complement deposits in the skin is a diagnostic hallmark of all pemphigoid diseases. However, recent studies showed that blistering might also occur independently of complement. This review reassesses the importance of complement in pemphigoid diseases based on current research by contrasting and contextualizing data from in vitro, murine and human studies.

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.

A specific antigen-antibody interaction triggers the cellular pathophysiology of bullous pemphigoid

Autoantibodies found in both the skin and sera of patients with bullous pemphigoid (BP) are capable of initiating the pathophysiology of blister formation that occurs in this disease. Current concepts of the pathophysiology of BP suggest that antibody alone cannot cause blister formation, but that antibody acts through complement-fixation, degranulation of mast cells and subsequent recruitment of leukocytes to the epidermal basement membrane. These leukocytes then release proteolytic enzymes which result in dermal-epidermal separation. This paper addresses the question of whether a specific molecule in the basement membrane zone is involved in the antigen-antibody reaction which triggers the cellular pathophysiology of BP. Immunoprecipitates of extracts of cultured human or mouse epidermal cells, radiolabelled with either [35S]methionine or 14C-labelled amino acids, indicated that sera from 25 of 26 BP patients precipitated the same molecule, as determined by co-migration on sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis (PAGE). This molecule is a protein with a mol. wt. of approximately 230 kd. A similar protein was identified in SDS extracts of normal human epidermis, as determined by immunoperoxidase staining of proteins separated by SDS-PAGE, then electrophoretically transferred to nitrocellulose sheets. Thus, in almost all cases of BP, one specific molecule of the epidermal basement membrane is involved in the antigen-antibody interaction that triggers the cellular pathophysiology of blister formation.

Dermatologic conditions reported in patients with rheumatoid arthritis

Dermatologists, while becoming increasingly involved in the diagnosis and management of patients with connective tissue diseases, have left rheumatoid arthritis relatively unexplored. An increased awareness of possible pathomechanisms of rheumatoid arthritis may allow for generalizations that lead to increased understanding of other connective tissue disorders. The types of cutaneous disorders that occur in association with rheumatoid arthritis include: vasoreactive dermatoses (e.g., various forms of vasculitis), which may occur secondary to the circulating immune complexes present in rheumatoid arthritis; autoimmune bullous disorders, which may occur in the setting of a suppressor T cell defect in rheumatoid arthritis; and various miscellaneous cutaneous associations. Hopefully, this review will lead to an increased understanding of both rheumatoid arthritis and the wide array of cutaneous associations of rheumatoid arthritis.

Bullous pemphigoid: a correlative study of autoantibodies, circulating immune complexes and dermo-epidermal deposits

Twenty bullous pemphigoid (BP) patients were studied to establish any correlation between free anti-basement membrane zone (BMZ) antibodies, circulating immune complexes (CIC) and dermo-epidermal junction deposits. CIC levels were evaluated by 2% polyethylene glycol (PEG) precipitation. The twenty patients were found to have IgG and/or C3 deposited in the BMZ. Eight of the twelve patients who had no free anti-BMZ antibodies displayed a positive in vivo C4 and/or CIq staining and high levels of CIC. Moreover, CIC were detected in only one patient with positive circulating free anti-BMZ antibodies. The presence of free anti-BMZ antibodies was generally found to correlate with the absence of cutaneous deposits of CIq and /or C4 and with negative CIC; on the other hand, the absence of free anti-BMZ antibodies was generally found to correlate with high levels of CIC and with deposits of C3 and CIq and/or C4. The absence of circulating free anti-BMZ antibodies in BP patients, could be explained by the formation of CIC. It is possible that BMZ antigens released from damaged tissue could combine with free antibodies and form complexes in the blood. The release could involve locally formed immune complexes. Elevated CIC levels were generally found to correlate with the presence of active disease.

Semiologic value of C1q and C4 cutaneous deposits. An immunofluorescent study

One hundred twenty skin biopsies from patients with different skin diseases were found to be positive for C3 cutaneous staining by immunofluorescence study. By the direct immunofluorescence method, we looked for C1q and C4 and immunoglobulin deposits in all those biopsies. C1q and/or C4 were only found in dermatoses with a recognised humoral immunologic mechanism; in some cases C1q and/or C4 deposits were found in the absence of immunoglobulins. The results showed that identification of C1q and C4 is important in routine immunopathologic studies, and provide interesting data of diagnostic value.

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.

Functional evidence for complement-activating immune complexes in the skin of patients with bullous pemphigoid

Previous immunofluorescent studies showing deposits of immunoglobulin and complement at the cutaneous basement membrane zone have provided evidence supporting a role for immune complexes in the pathogenesis of bullous pemphigoid. In this study the functional activity of the deposits has been examined using leukocyte attachment, a method for detecting and quantitating the biological activity of complement-activating immune complexes in tissues. When peripheral blood leukocytes suspended in serum complement were incubated with cryostat sections of lesional and adjacent normal-appearing skin from 9 patients with pemphigoid, skin from 11 normal controls and lesional skin from 14 nonpemphigoid disease controls there was significantly greater attachment of leukocytes to the basement membrane zone of lesional bullous pemphigoid skin compared to normal-appearing pemphigoid skin and skin of both control groups. A significant reduction in attachment in the absence of serum complement suggested the reaction was dependent on activation of complement by tissue-deposited complexes. Although leukocyte attachment was greater in lesional than normal-appearing pemphigoid skin, a comparison of the incidence and intensity of cutaneous IgG and complement immunofluorescence between the 2 groups showed no significant differences. Furthermore, no correlation between leukocyte attachment and serum titers of immunoglobulin G or complement-binding anti-basement membrane zone antibodies was observed. These results suggest that immune reactants in lesional pemphigoid skin are functional complement-activating immune complexes, that differences exist between the activity of complexes in lesional and normal-appearing pemphigoid skin and may explain why lesions develop at some sites and not others.

Coexistent atypical bullous pemphigoid and systemic lupus erythematosus

A vesiculobullous eruption with clinical and histological features of bullous pemphigoid developed in a 38-year-old woman with proved systemic lupus erythematosus. The patient had a sulphone responsive blistering disease that was characterized by pruritic subepidermal bullae and linear, predominantly IgA basement membrane zone deposition and IgA pemphigoid antibodies in her sera. Because both diseases are associated with immune complexes of special immunoglobulin classes, this association may not be entirely fortuitous.

Pemphigoid antibody mediated attachment of peripheral blood leukocytes at the dermal-epidermal junction of human skin

It has been proposed that cutaneous inflammation and blister formation in bullous pemphigoid is caused by antibodies to the cutaneous basement membrane zone which active complement, thereby, attracting leukocytes to the dermal-epidermal junction. There is, however, no functional evidence which supports a role for pemphigoid antibodies in complement activation or leukocyte activity in skin. This study describes the in vitro attachment of human peripheral blood leukocytes to the dermal-epidermal junction of cryostat skin sections treated with 9/13 pemphigoid sera containing antibodies to the cutaneous basement membrane zone. A requirement for complement in the reaction was supported by the findings that only complement-fixing pemphigoid sera mediated the leukocyte response, a strong correlation existed between complement-fixation titers and leukocyte attachment titers and only leukocytes suspended in fresh serum but not buffer or heat inactivated serum attached at the junction. A requirement for antibody was supported by the observation that IgG fractions of 4 pemphigoid sera were as effective as whole sera in mediating leukocyte attachment. The leukocyte response was shown to be specific for complement-fixing pemphigoid sera since it was not observed with noncomplement-fixing sera or sera from 15 normal human and 22 nonpemphigoid disease controls. This study offers functional evidence for an interaction between pemphigoid antibody, complement and leukocytes in the immunopathogenesis of bullous pemphigoid and demonstrates that complement-fixing antibasement membrane zone antibodies may be important in initiating the cellular inflammatory events observed near the dermal-epidermal junction in vivo.