Complement factor D in serum. An indicator of glomerular filtration rate in chronic inflammatory arthritis

Adsorption of complement factor D by polyacrylonitrile dialysis membranes

Factor D, an essential enzyme of the alternative pathway (AP) of complement, accumulates in end-stage renal failure (ESRF). Polyacrylonitrile (PAN) membrane activates complement poorly and has been shown to adsorb C3a, the main anaphylatoxin released during complement activation. In the present work we investigated whether factor D might be adsorbed on PAN. In vitro there was a loss of hemolytic factor D when normal human serum (NHS) was incubated with PAN dialysis fibers, whereas no loss was observed with cuprophan (Cu) fibers. There was a dose and time dependent binding of purified radiolabeled factor D to PAN but not to Cu. The hemolytic function of factor D released from PAN by 2 M NaCl was normal. By contrast, factor D was inactive while adsorbed to PAN fibers. When 50 ml of NHS or 100 ml of whole blood were passed through a new hollow fiber PAN dialyzer 95% of factor D was adsorbed. The eluate from a PAN filter which had been used for dialysis in a patient with ESRF contained 38.4 mg of hemolytic factor D, representing 34% of the proteins eluted. By immunoblotting, antigenic factor D from the PAN eluate was identical to purified human factor D. In six patients there was a 81.4% decrease in hemolytic factor D in blood after dialysis with PAN, contrasting with a 9.6% decrease in those dialyzed with cellulose acetate. No factor D was found in the dialysis fluid of PAN dialyzers, indicating that PAN removed factor D mainly by adsorption. In conclusion, PAN has a significant capacity to adsorb factor D, a reaction that might contribute to the diminished capacity of PAN membrane to activate the AP of complement. Whether the efficient removal of large amounts of factor D might be beneficial in uremic patients remains to be defined.

Complement levels and circulating immune complexes in a controlled, longitudinal, multicentre study on effects of intravenous immunoglobulin in adults with AIDS-related complex/Walter-Reed 5. The ARC-IVIG Study Group

The complement system, as the effector mechanism of the antigen-antibody reaction, and the levels of circulating immune complexes in a 1-year, double-blind, randomized, placebo-controlled study served as laboratory parameters to assess the effect of long-term high-dose intravenous immunoglobulin (IVIG) therapy in 30 adult patients (2 x 15) with AIDS-related complex/Walter-Reed 5 (ARC/WR5). We obtained no evidence of an adverse effect in such patients of high-dose IVIG administered over a 6-month period: none of the parameters studied showed a significant difference between the two groups of patients. In both groups, using data before the first infusion or using data of the whole study, a correlation between circulating immune complexes and classical complement pathway activation was found. The most striking increase was seen in the two groups of patients for functional serum factor D. The accumulation of serum factor D was not paralleled by an increase in serum creatinine. In patients with disease progressing from ARC to AIDS within the study period, an accumulation of serum factor D was not more or less pronounced than in those who remained in the ARC stage. Accumulation of factor D was not related to the clinical score as assessed in this study.

Metabolism of complement factor D in renal failure

Factor D is an essential enzyme of the alternative pathway of complement. Its plasma concentration increases approximately tenfold in end-stage renal failure (ESRF). To analyze its metabolism in humans, we injected purified radiolabelled factor D into 5 healthy individuals and 12 patients with various renal diseases or renal failure. Fractional metabolic rates (FMR) and extravascular/intravascular distributions (EV/IV) were calculated using a compartmental model. The FMR was very rapid in normal individuals (mean 59.6%/hr; range 74.1 to 50.5), significantly diminished in the five patients with ESRF (5.7%/hr; 7.0 to 2.8; P less than 0.004), and correlated well with the creatinine clearance (r = 0.89; P less than 0.001). The extrarenal catabolic rate was not modified in renal failure. Despite a significant inverse correlation between plasma levels of factor D and creatinine clearance [r = 0.68; P less than 0.002], factor D levels were not a sensitive indicator of renal function because the synthesis rate (SR) varied widely from one individual to another (mean SR: 62.9 micrograms/kg/hr; 14.9 to 136.5). Factor D synthesis was not significantly altered by renal function, and did not correlate with C-reactive protein, suggesting that factor D is not an acute phase protein. The proportion of intact factor D elimination in the urine was increased in patients with tubular dysfunction (up to 15% compared to less than 0.2% in normal individuals) confirming that under normal circumstances factor D is filtered through the glomerulus and catabolized by tubular cells.(ABSTRACT TRUNCATED AT 250 WORDS)