The in vivo metabolism of C3 in human glomerulonephritis and after renal transplantation

Abstract

Metabolic investigations of complement component C3 have been performed to study pathogenetic mechanisms in patients with glomerulonephritis and after renal transplantation. Purified and biologically active ¹²⁵I-labelled C3 was given intravenously together with ¹³¹I-albumin to nine patients with different forms of glomerulonephritis and nine allograft recipients at different stages after renal transplantation.

Control studies were performed in 16 normal individuals. The fractional catabolic rate (FCR) of the proteins was calculated with the metabolic clearance method (U/P ratio) and/or by analysis of the plasma radioactivity disappearance curve. An increased FCR of C3 was found in three patients with glomerulonephritis. A modestly elevated FCR of C3 was found in all but one of the transplant patients as calculated by the U/P ratio, while the FCR was high in only two when calculated from plasma radioactivity disappearance. Slight increases of C3 catabolism were found during two suspected rejection episodes, but may have been due to a general increase in protein turnover. The serum level of C3 was reduced in two recipients and in one of these the FCR of the protein was elevated. The remaining patients had normal or increased C3 levels. Judged from these results, activation of complement was only of modest importance in the patients studied.

Key-words:

• C3 metabolism
• glomerulonephritis
• renal transplantation