Dermal-epidermal deposition of complement components and properdin in systemic lupus erythematosus

Skin lesions and clinically normal skin of thirteen patients with systemic lupus erythematosus (SLE) were examined, by the use of immunofluorescent techniques, to determine the presence of CIq, C3, C3 proactivator (C3PA), properdin, immunoglobulins (IgG, IgA, and IgM), and fibrin. IgM deposition was present in all thirteen skin lesions and in eleven normal areas tested, whereas IgG deposition occurred in eleven of the lesions but in only six normal areas. IgA was the least frequently encountered immunoglobulin. CIq deposition occurred in all thirteen skin lesions, and C3 deposition was present in twelve. Seven of nine and eight of eleven clinically normal areas demonstrated CIq and C3 deposition, respectively. Although less intense that CIq and C3 deposition, properdin deposition occurred in eight of the thirteen skin lesions tested but in only two of nine normal areas. C3PA deposition was of greater intensity than was properdin, but was seen in only five lesions and three clinically normal areas. Seven skin lesions and two normal areas also demonstrated fibrin deposition. Although alternate pathway activation is apparent, our findings suggest that the classical pathway (CI to C9) is the primary complement pathway involved in SLE skin.