Cathepsin D-like activity in serum of patients with systemic lupus erythematosus.

Cathepsin D-like activity was measured in the sera of 62 patients with active systemic lupus erythematosus (SLE), 9 patients with progressive systemic sclerosis, 9 patients with chronic glomerulonephritis and 18 with glomerulonephritis with nephrosis syndrome. The in vitro and in vivo effect of corticosteroid treatment on enzyme activity was also investigated. Cathepsin D-like activity appeared measurably in the sera of all patient groups but not in controls. The highest values were found in SLE patients. The increase in serum activity correlated with renal involvement. In vivo corticosteroid treatment significantly decreased serum activity in all groups except in systemic sclerosis patients. In vitro prednisolone treatment decreased enzyme activity in a dose-dependent manner. Determination of serum cathepsin D-like activity seems to be useful in the establishment of diagnosis and prognosis of SLE. Cathepsin D may be of pathogenetic significance in autoimmune disease especially in SLE.