The use of antibody to C5b-9 in the subclassification of lupus erythematosus.

Fifty-five patients with biopsy-proven cutaneous lupus erythematosus (LE) were identified in whom a prospective and retrospective review of the clinical and laboratory data allowed subclassification into systemic (SLE), subacute (SCLE), or discoid (DLE) variants. In addition to conventional direct immunofluorescence, an indirect immunofluorescent technique, using a monoclonal antibody, was employed to assess deposition of the membranolytic attack complex (C5b-9) in skin lesions. Deposition of C5b-9 within the epidermis correlated with a diagnosis of SCLE with or without antibodies to Ro and was seen in SLE patients with antibodies to extractable nuclear antigens Ro, La, Sm, and RNP, and in DLE patients with positive antinuclear antibodies and/or extracutaneous manifestations. In the SLE group, vascular C5b-9 deposition was present in six patients. Of these, four had circulating lupus anticoagulant, one had lymphocytic vasculitis, and two had antibodies to Ro. In two patients with SLE there was keratinocyte decoration for immunoglobulin G but not for C5b-9, in the absence of seropositivity for antibodies to Ro, La, Sm, and ribonucleoprotein (RNP). The immunohistological examination of skin lesions using a monoclonal antibody to C5b-9 is a valuable adjunct in the subclassification of LE. The presence of C5b-9 within skin lesions of patiens with LE implies a pathogenic role for complement-mediated pore formation.