FCN1

Ficolin-1 (FCN1), also known as M-ficolin or P35, is a secreted pattern recognition receptor belonging to the collagen-containing lectin family. It binds pathogen-associated molecular patterns (PAMPs) on microbial surfaces through its fibrinogen-like domain, initiating complement activation via the lectin pathway. FCN1 forms complexes with MASPs (MBL-associated serine proteases) to cleave C4 and C2, generating C3 convertase critical for opsonization and pathogen clearance. Its activity intersects with innate immune signaling, particularly Toll-like receptor (TLR) pathways, amplifying inflammatory responses. Dysregulated FCN1 expression is implicated in chronic inflammation and tissue damage.

Genetic polymorphisms in FCN1 correlate with susceptibility to bacterial infections, including pneumonia and sepsis, as well as autoimmune disorders like rheumatoid arthritis. Elevated FCN1 levels are observed in atherosclerosis, linking it to endothelial dysfunction. While no FCN1-targeted therapies are clinically approved, complement inhibitors such as anti-C5 antibodies (e.g., eculizumab) indirectly modulate its pathway. Recent studies explore FCN1 as a biomarker for inflammatory diseases and a potential therapeutic target through monoclonal antibodies or lectin pathway blockade strategies.