Human Ficolin-1 Alexa Fluor® 594-conjugated Antibody

Human Ficolin-1 (fibrinogen/collagen-like), also called M-ficolin, is a member of the ficolin family of secreted pattern recognition proteins in the lectin complement activation pathway (1‑3). Ficolin-1 is expressed by monocytes, neutrophils and type II alveolar epithelial cells (2‑5). It is proposed to be a locally-acting lectin released in a regulated manner (4). Ficolin-1 is not found in plasma, but is detected on the surface of circulating monocytes (4‑6). The 35 kDa, 326 amino acid (aa) human Ficolin-1 contains a 28 aa signal sequence, an N-terminal collagen domain and a C-terminal fibrinogen-like (FBG) domain that includes a calcium binding site and one potential N-glycosylation site. Both the collagen and FBG domains mediate trimer formation (7). Like Ficolin-2, larger homo-multimers of Ficolin-1 exist and are likely formed by disulfide bonds at the N-terminus. Sizes corresponding to 12 or 18 subunit oligomers are reported (4, 6, 7). The FBG domain of Ficolin-1 binds microbial ligands that contain acetylated compounds (6). Ligands identified include N-acetyl glucosamine, N-acetyl galactosamine and sialyl-N-acetyllactosamine (4‑7). Like other ficolins, Ficolin-1 associates with, and activates the MBL-associated serine protease (MASP) complex, which activates the complement pathway by cleaving C4, contributing to the innate immune response (4‑6). Mature human Ficolin-1 shares 76%, 61%, 61%, 76% and 81% aa identity with mouse Ficolin-2 (8), and mouse, rat, canine and porcine Ficolin-1, respectively. It shares 84% and 46% aa identity with human Ficolin-2 and Ficolin-3, respectively. The Ficolin-1 gene is polymorphic, showing at least ten single nucleotide polymorphisms in the promoter and coding regions (1).