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

To assess the relative roles of the classic and alternative pathways of complement activation in chronic discoid lupus erythematosus (CDLE), serum levels of properdin, C3, and C4, and deposition of these proteins in the dermal-epidermal junction (DEJ) of 20 CDLE patients were compared to the findings in patients with clinically active and inactive SLE. Properdin was demonstrated in the DEJ of 10 of 14 (71%) histologically typical skin lesions from patients with CDLE, usually in association with deposits of immunoglobulin, C3, and C4. Properdin levels in CDLE patients were significantly increased (137 +/- 34%) (P less than 0.05) when compared to normal controls (101 +/- 18%) or to patients with clinically active SLE (89 +/- 32%). C3, C4, DNA-binding, and antinuclear antibody tests in CDLE were indistinguishable from those in normals, but significantly different from patients with active SLE (P less than 0.05). The complement profiles of patients with clinically inactive SLE resembled those of CDLE patients more closely than those of active SLE patients.