Fibrinogen is a component of a novel lipoprotein particle: Factor H–related protein (FHRP)–associated lipoprotein particle (FALP)

Abstract

AbstractWe have previously described a novel lipoprotein particle consisting of phospholipids, apolipoprotein A-I (apoAI), lipopolysaccharide binding protein (LBP) and Factor H-related proteins (FHRP), and we termed these particles FALP (FHRP-associated lipoprotein particles). Highly purified preparations of FALP contain variable amounts of an unidentified polypeptide triplet of Mr ∼85 000 (tp85). Here we report that tp85 represents fragment D of fibrinogen, as confirmed by N-terminal amino acid sequencing and Western blot analysis with an antifibrinogen antibody. The physical association of fibrinogen with other components of FALP in plasma was further confirmed by sandwich ELISA by using monoclonal antibodies against apoAI, FHRP or LBP to capture the particles and polyclonal antifibrinogen as the detecting antibody. Furthermore, affinity chromatography with anti-FHRP-1–specific IgG showed that fibrinogen is co-immunodepleted with FALP and approximately 17% of total plasma fibrinogen are bound to FALP. LBP is a lipid transfer protein that moves lipopolysaccharide (LPS) to a binding site on CD14 or high-density lipoprotein (HDL). To determine whether fibrinogen affects the lipid transfer activity of LBP on FALP, this activity was measured in FALP prepared with and without fibrinogen. Neither activity of LBP was affected by fibrinogen. The abundance of FALP suggests, instead, an effect of FALP on the function or clearance of fibrinogen or fragment D. (Blood. 2000;95:198-204)