CMPGN with hypocomplementemia appears to be one identifiable form of progressive and destructive glomerulonephritis, but whether this is a specific pathogenetic entity has not been proven. The clinical features of the "disease" include presentation with either asymptomatic proteinuria and hematuria, nephrotic syndrome, or gross hematuria and an acute nephritic syndrome. Morphologic studies reveal extensive mesangial cell proliferation and increased matrix with thickening of the glomerular capillary. Deposits of C3 and properdin uniformly are found predominantly in a peripheral lobular distribution by immunofluorescent microscopy; immunoglobulins are seen less consistently. These deposits are different from those seen in other glomerular diseases.

Serum complement abnormalities have also been demonstrated: depression of C3t (and ß1C/ß1A) with relatively normal earlier components, evidence for in vivo breakdown of C3 by labeled isotope studies and elevated α2D, presence of a serum inhibitor that inactivates guinea pig C3t and a pseudoglobulin lytic factor that in combination with a normal serum cofactor enzymatically cleaves C3 to α2D and ß1A.

The terminal complement inactivation and the uniform presence of properdin in these deposits suggesting an alternate pathway of immune injury must be balanced against immunopathologic observations which demonstrate glomerular deposits of immunoglobulins and earlier complement components. It is possible that both mechanisms may be operative in CMPGN.

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