URINARY C4 EXCRETION IN SYSTEMIC LUPUS-ERYTHEMATOSUS

The fourth component of complement (C4) in urine was measured in 19 pa tients with systemic lupus erythematosus (SLE). Urinary C4 was detecta ble in all SLE patients using an enzyme linked immunosorbent assay. In 11 of 13 patients whose urinary C4 was serially measured, a decrease of urinary C4 was found in parallel with a decrease of disease activit y of SLE. In the remaining 2 patients, the amount of C4 increased prec eding a flare-up of the disease. The measurement of urinary C4 may be useful in evaluating the disease activity of SLE in individual patient s and sometimes in predicting the flare-up of the disease. The specifi c hemolytic activity of excreted C4 and Western blotting analysis show ed that urinary C4 consisted mainly of degraded fragments of C4. In tw o cases, camostat, a serine protease inhibitor, rapidly decreased the urinary C4 excretion, suggesting that the complement activation occurr ed in the glomerulus in lupus nephritis.