Background: The membrane attack complex (MAC; C5b-9) localizes in the basement membrane zone (BMZ) of cutaneous lesions from patients with lupus erythematosus (LE) and has been implicated in the pathogenesis of this disease. Objective: Our purpose was to compare the frequency of MAC deposition with that of immunoglobulin and C3 deposition (lupus band). Methods: We studied 56 skin biopsy specimens from 42 patients with LE by direct immunofluorescence. Results: MAC was deposited in a granular pattern at the BMZ in 29 of 38 biopsy specimens (76%) from lesional skin; 5 of 38 specimens (13%) had focal or weak segmental deposition and 4 of 38 (11 %) were negative. In contrast, IgG, IgM, IgA, and C3 were detected in 16 of 38 specimens (42%), 30 of 38 (79%), 4 of 38 (11%), and 22 of 38 (58%), respectively. None of the uninvolved skin biopsy specimens was MAC positive, although 4 of 18 (22%), 5 of 18 (28%), 1 of 18 (6%), and 2 of 18 (11%) were positive for IgG, IgM, IgA, and C3, respectively. Conclusion: MAC deposition in lesional skin appears to be a relatively sensitive and specific marker for cutaneous LE and may be useful as an adjunct to the “lupus band” test.
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