Abstract
Background: Unlike most complement proteins, complement factor D is believed to be synthesized not by the liver but exclusively by adipose tissue. Method: Culture supernatants obtained from primary culture of normal human hepatocytes were assayed for factor D by ELISA and analyzed by Western blotting. Results: When normal hepatocytes were cultured in protein-free medium without addition of any stimulator for 5 days, factor D was detected in the supernatants at levels as high as 331.07 ± 41.38 μg/106 cells. Addition of TNF-α, IFN-γ, IL-1β or LPS to the medium did not result in any distinct effect on the amounts of secreted factor D. Reversible inhibition of factor D secretion by these cells was observed when cultured in the presence of cycloheximide. By immunoblot analysis, secreted factor D exhibited double bands, one with a molecular weight similar to factor D in normal human serum and the other with a slightly larger molecular weight. Conclusion: Normal human hepatocytes synthesize factor D constitutively. The liver may be a major source of plasma factor D.