DEPOSITION OF MEMBRANE ATTACK COMPLEX IN CUTANEOUS LESIONS OF LUPUS-ERYTHEMATOSUS

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%) bad focal or weak segmental deposition and 4 of 3 8 (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.