Properdin was demonstrated by indirect immunofluorescence in glomeruli of six of seven patients with lupus nephritis, two of whom had membranous lupus nephritis, one focal proliferative lupus nephritis, and three of four diffuse proliferative lupus nephritis. Properdin was not present in a kidney from a patient with systemic lupus erythematosus but no clinical or pathological evidence of renal disease or in seven of eight patients with other renal diseases. Properdin was demonstrable in the dermal-epidermal junction of the erythematous rash in one of two patients with systemic lupus. Immunoglobulins and complement components (C3, C4) were also present in tissues studied.

The data suggest that the properdin system participates in complement activation in the disease and that both the classic pathway, involving C1, C4 and C2, and the alternate pathway of complement activation are involved in the pathologic changes in this disease.