HUMAN LIVER-DERIVED HEP G2 CELLS PRODUCE FUNCTIONAL PROPERDIN

Properdin stabilizes the alternative complement pathway C3 convertase and is synthesized by monocytes and myelomonocytic cell lines. Hepatic production of properdin has never been documented, although most othe r complement components are synthesized by liver. Human liver-derived Hep G2 cells were examined for the ability to produce properdin by usi ng the polymerase chain reaction (PCR). Amplified properdin message wa s detected by using Southern transfer and hybridization to a murine pr operdin cDNA probe. Sequencing of the PCR product revealed that the He p G2 message was nearly identical to the cDNA sequence from U937 cells . Subsequently Hep G2 cultures were stimulated with interleukin (IL-6) , 25 mu g/ml, and culture supernatants were assayed for the presence o f properdin by using dot blots. Properdin concentration increased over time, and we found no obvious difference between properdin production by IL-6-stimulated and unstimulated Hep G2 cells. Finally, alternativ e pathway decay assays confirmed the presence of functionally active p roperdin in the culture supernatant. Thus, functional properdin is a p roduct of Hep G2 cells, suggesting that biosynthesis of properdin may occur in hepatocytes. Properdin synthesis was not augmented by IL-6, a finding that is consistent with previous observations that properdin is not an acute phase reactant.