Pathways of complement activation in chronic discoid lupus: serologic and immunofluorescence studies

The use of C3d and C4d immunohistochemistry on formalin-fixed tissue as a diagnostic adjunct in the assessment of inflammatory skin disease

BACKGROUND

Direct immunofluorescent (DIF) testing defines an important diagnostic adjunct in the classification of various inflammatory skin conditions; it requires fresh tissue, a laboratory equipped to perform the procedure, and a pathologist skilled in its interpretation. Although advances have been made in the development of antibodies that can be applied to paraffin-embedded tissue, there has been no reported success on the application of paraffin tissue-based immunohistochemistry as a potential substitute for DIF testing on skin biopsy material.

OBJECTIVE

We applied C3d and C4d immunohistochemistry on paraffin-embedded, formalin-fixed tissue to define a potential application of these two antibodies as a diagnostic adjunct in the evaluation of various inflammatory skin diseases.

DESIGN

A natural language search identified cases submitted for both light microscopic and DIF studies from July 2006 to August 2007. We prospectively included similar cases encountered from August 2007 to March 2008. We correlated the C3d and C4d staining pattern with the DIF and light microscopic findings.

RESULTS

All cases of scarring discoid lupus erythematosus (LE) (20/20) and systemic LE (5/5) showed prominent granular C3d along the dermoepidermal junction (DEJ) and a positive lupus band test result in the latter by DIF. All systemic LE cases demonstrated granular DEJ C4d with C3d or C4d in blood vessels (BV). There was a negative lupus band test result without DEJ C3d or C4d in all cases of subacute cutaneous lupus erythematosus (SCLE) (15/15). There were, however, deposits of C4d within epidermal keratinocytes (7/7), corresponding to IgG decoration of keratinocytes by DIF and the presence of anti-Ro antibodies. Dermatomyositis cases showed prominent mural C3d and C4d in BV corresponding to C5b-9 by DIF (12/12) and one case of hydroxyurea-induced dermatomyositis lacked this staining. Although by DIF all dermatomyositis cases had a negative lupus band test result, 25% of cases showed staining for C3d along the DEJ (3/9). Bullous pemphigoid cases demonstrated homogenous DEJ C3d (17/17) whereas C4d was characteristically negative; there was 100% concordance with linear IgG and C3d by DIF. Eighty two percent of pemphigus cases demonstrated prominent intercellular C3d and C4d, roughly mirroring the intercellular pattern for IgG and complement seen by DIF (9/11). Porphyria cases showed homogeneous and granular C3d (11/11) and C4d (7/11), mirroring the vascular immunoglobulin and C5b-9 by DIF. All cases of urticarial (5), leukocytoclastic (6), and lymphocytic (1) vasculitis exhibited prominent mural C3d and C4d in BV, whereas Henoch-Schönlein purpura (10/10) showed primarily mural BV C3d without C4d, with IgA by DIF. Three cases of relapsing polychondritis showed C3d and C4d within chondrocyte nuclei (3/3), in contrast to negative staining in chondrodermatitis nodularis helicis (0/2). Hypersensitivity reactions were negative for C3d and C4d.

LIMITATIONS

The small sample size in each category is a limitation. The lack of literature precedent with regard to immunohistochemical assessment of extracellular antigens on paraffin-embedded tissue in skin samples is another limitation of this study.

CONCLUSIONS

When correlated with the light microscopic and clinical findings, the C3d and C4d assay has significant application in the assessment of select inflammatory skin diseases including vasculopathic conditions, collagen vascular disease, and autoimmune vesiculobullous disorder. It may prompt further DIF testing or, in some instances, may even define a reasonable substitute for DIF and/or add to the morphologic assessment of a biopsy specimen submitted for routine light microscopic assessment primarily in the setting of autoimmune vesiculobullous disease and collagen vascular disease.

Antibodies to single-stranded DNA in patients with discoid lupus erythematosus

Sera from 31 patients with discoid lupus erythematosus were examined for the presence of antibodies to single-stranded and native DNA. None of these sera had antibodies to native DNA. When rabbit anti-human IgM was used, 6 of 28 patients had elevated binding, whereas only 1 of 29 patients had abnormal binding when antiIgG was used. The IgM nature of this response was confirmed when we demonstrated the binding activity in heavy fractions from gel filtration. We concluded that at least one-fifth of patients with discoid lupus erythematosus have IgM antibodies to single-stranded DNA.

Cutaneous localization of the membrane attack complex in discoid and systemic lupus erythematosus

Biopsy specimens of skin lesions from three patients with discoid lupus erythematosus and six patients with systemic lupus erythematosus contained the membrane attack complex, which comprises C5b through C9, as well as immune complexes at the dermal-epidermal junction. The basilar epithelium in these areas was vacuolated and edematous, and the dermis contained an inflammatory infiltrate. In contrast, 19 of 29 specimens of normal-appearing skin from patients with discoid or systemic lupus erythematosus showed only immune complexes at the dermal-epidermal junction, without the membrane attack complex. The other 10 specimens, all from patients without cutaneous involvement, showed neither immune complexes nor membrane attack complexes. These data suggest that immune complexes within skin lesions selectively generate the assembly of the membrane attack complex, which mediates membrane injury. A synergistic interaction of immune complexes and cofactors may be required to activate complement in areas of skin that are predisposed to tissue injury.

Clq deposits at the dermoepidermal junction: a marker discriminating for discoid and systemic lupus erythematosus

Discoid lupus (DL) and systemic lupus erythematosus (SLE) patients have been comparatively evaluated for complement and immunoglobulin deposits at the dermoepidermal junction (DEJ) by immunofluorescence (IF). When IF was positive, Clq deposits were quasi-constantly found in SLE patients with or without skin lesions (90%), while Clq was found in only 29% of the DL patients. Of the 42 DL patients followed-up to at least 2 years, 4 have eventually evolved a systemic disease. In these 4, neither cryoglobulinemia nor significant titers of ANA had been found at the time of presentation. Only 1 of these 4 patients had initially circulating immune complexes (P.E.G) and a positive IF in a normal sunprotected area. Clq deposits at the DEJ were present in all these 4. Of the remaining 38 DL patients, none has progressed to SLE: 8 had had significant titers of ANA, 5 had had circulating immune complexes, and 3 others had had cryoglobulinemia. Thus Clq deposits in DL cases are associated with a relatively high incidence of eventual systemic disease. Taken together, these data suggest that Clq deposits in skin may be a marker for systemic lupus.

Lupus erythematosus

Lupus erythematosus (LE) is a multisystem disease. Genetic predisposition, altered immunity, hormones, drugs, viruses, and ultraviolet light all may play a role in etiology. A wide range of cutaneous lesions occur, and variants such as subacute cutaneous LE, complement-deficient LE, and neonatal LE have recently been emphasized. Management of the LE patient, including appropriate diagnostic studies and therapy relevant to the dermatologist, is discussed in the review.

The specificity and clinical usefulness of the lupus band test

Granular deposition of immunoglobulin at the dermoepidermal junction is characteristic, but not pathognomonic, of lupus erythematosus. When rigid criteria for the lumpus band test are used, a positive result is highly specific. A positive band test is found in clinically normal skin and lesional skin of systemic lupus patients, and in lesional skin of discoid lupus patients. A positive band test is found infrequently in clinically normal skin of patients with other connective tissue disorders. Cutaneous lupus may be difficult to separate from other morphologically similar disorders. The lupus band test is useful in differential diagnosis because other disorders have either a specific pattern of immunoglobulin deposition or no immunoglobulin deposition. The mechanisms of immunoglobulin deposition at the epidermal basement membrane zone are discussed as well as pertinent clinical correlations of the positive band test.