URINARY-EXCRETION OF PROTECTIN (CD59), COMPLEMENT SC5B-9 AND CYTOKINES IN MEMBRANOUS GLOMERULONEPHRITIS

Protectin (CD59) is a low molecular weight glycophosphoinositol-anchor ed inhibitor of the membrane attack complex of complement (MAC) that i s present, for example, on the membranes of endothelial cells and on e pithelial cells of glomeruli and distal tubuli. To examine for the pos sibility that CD59 becomes detached from cell surfaces following cell injury, this study evaluated renal excretion of CD59 in patients with idiopathic membranous glomerulonephritis (MGN; N = 21), diabetic nephr opathy (DNP; N = 15) and in healthy control subjects (N = 13). CD59 in human urine was quantitated by a competitive solid-phase radioimmunoa ssay having approximate to 13 kDa soluble urinary CD59 as a standard. Immunofluorescence microscopy demonstrated a decreased expression of C D59 in the glomeruli of MGN patients. Using a Triton X-114 phase separ ation method 91 to 97% of urinary CD59 was found to be in a soluble fo rm without anchor-associated phospholipid. The mean (+/-SEM) level of urinary CD59 was 5.6 +/- 0.2 mu g/ml in MGN patients, 3.7 +/- 0.4 mu g /ml in healthy controls (P < 0.001) and 2.6 +/- 0.1 in PNP patients (P < 0.001). When related to urinary creatinine (U-Cr) the corresponding values were 11.9 +/- 5.6, 4.8 +/- 0.3 (P = 0.021) and 4.4 +/- 0.2 (P < 0.002), respectively. The amount of CD59 in urine correlated with th e urinary excretion of soluble terminal complement complexes, SC5b-9 ( r = 0.594), P < 0.006) in MGN patients. The excretion of CD59 also cor related with the excretion of the inflammatory mediator IL-1 beta (r = 0.671, P = 0.001) but not with TNF-alpha (r = 0.314, P = 0.178). No c orrelation of CD59 excretion was observed with duration of the disease , level of proteinuria, serum albumin concentration or serum creatinin e level. Based on these findings we speculate that the increased excre tion of CD59 into urine in MGN patients is due to complement activatio n and inflammation induced shedding of CD59 from glomerular cells.