Properdin levels in systemic lupus erythematosus and membranoproleferative glomerulonephritis.

The participation of the classical complement pathway, of the properdin system and of the C3b amplification system, is studied in forty-six patients suffering from systemic lupus erythematosus (SLE) and in forty-two patients with membrano-proliferative glomerulonephritis (MPGN). In SLE the decrease of C3 is associated with a decrease of the early acting complement components as well as a decrease of C3PA and properdin. The decrease of C3PA is closely related to the C3 level. This pattern correlates well with a major involvement of the classical complement pathway and of the C3b amplification system. In MPGN the decrease of C3 is associated with normal values of early acting complement components and with a decrease of C3PA and properdin levels. There is no clear relationship between C3PA levels and C3 levels, but C3 levels are closely related to the properdin levels as seen by regression analysis. This pattern is suggestive of a major involvement of the properdin system in MPGN.