Two cases who showed C3 or C4 nephritic factor activity

Abstract

C3 nephritic factor (C3NeF) was found in patients with membranoproliferative glomerulone phritis (MPGN) and in some cases of partial lipodystrophy. C3NeF was supposed to be the auto-antibody to C3 convertase (C3bBb) of the alternative complement pathway and stabilize it, resulting in characteristic complement profile in their serum.Recently C4 nephritic factor (C4NeF), which was thought to be the auto-antibody to C3 convertase of the classical complement pathway (C4b2a), was found in patients with systemic lupus erythematosus (SLE) or poststreptcoccal glomerulonephritis.We found C4NeF activity both in serum and urinary IgG fraction of a patient with SLE, who presented nephrotic syndrome and MPGN at the time of renal biopsy. The C4NeF activity in serum and urine disappered after the treatment of steroid therapy.We also found C3NeF activity only in serum IgG fraction, not in urinary IgG fraction, of a patient with ulcerative colitis, sclerosing cholangitis and chronic glomerulonephritis, of which biopsy specimen showed MPGN. However, the activity was atypical in comparison with C3NeF reported so far, because of its unstability and weakness in activating complement of normal human serum and it suggested heterogeniety of C3NeF.While C4NeF activity was detected both in serum and in urine, C3NeF was found only in serum. Thinking into consideration that selectivity of the urinary protein from the two patients did not differ, we speculated C3NeF had high affinity to the glomerulus.