Medicine & USMLE

Lectin Complement Pathway

  1. Common Complement Pathway
  2. Classical Complement Pathway
  3. Alternative Complement Pathway
  4. Lectin Complement Pathway


The Lectin Complement Pathway is one of three initiating pathways of the complement system. The pathway is initiated by Mannose-binding Lectins (MBLs) that bind mannose, a sugar found on the surface of many pathogens. Lectin binding to mannose creates a complex that cleaves C2 and C4. Cleaved C2 and C4 then combine to form a C3 convertase. This C3 convertase then continues onwards as part of the common pathway of complement activation. The primary purpose of the lectin complement pathway is to kill microbes expressing mannose.

Key Points

  • Lectin Complement Pathway
    • One of three initiating pathways of the complement system
    • Goal is to kill microbes expressing mannose
    • Mannose-binding Lectin (MBL) binds mannose on pathogen surfaces
      • Mannose is expressed on many microbial surfaces
    • Forms a complex that cleaves C4 and C2
      • MASPs (mannose-associated serine proteases) cleave C4 and C2
    • Cleaved C4 and C2 combine to form C3 Convertase