CLASSICAL
This hexameric initiator protein complex binds to antigen-antibody complexes to launch classical complement activation.
What is C1q (or C1 complex)
This soluble pattern recognition receptor binds repeating terminal mannose residues on microbial surfaces to trigger the lectin pathway
What are mannose binding lectins?
constitutively active protease that cleaves bound Factor B into Ba and Bb
What is Factor D?
These small soluble complement cleavage fragments act as inflammatory mediators by causing vasodilation and attracting leukocytes
What are C3a and C5a?
Formed by the sequential assembly of C5b through C9, this pore-forming structure directly lyses target cells
What is membrane attack complex (MAC)?
Attaching a newly generated C3b fragment to the C4b2a C3 convertase forms this enzyme
What is C5 convertase? C4b2a3b
serine proteases associate with Mannose-Binding Lectin (MBL) to serve functions analogous to C1r and C1s
What are MASP-1 and MASP-2 (MBL-Associated Serine Proteases)?
This positive regulatory protein binds to and stabilizes the alternative C3 convertase against rapid decay on microbial surfaces.
What is Properdin (Factor P)?
This primary complement fragment coats microbial surfaces to act as an opsonin recognized by phagocyte receptors
What is C3b?
Common enzyme complex that is generated by BOTH the classical and lectin pathways to cleave C3
what is C4b2a (C3 convertase)?
unique chemical feature of newly generated C4b enables it to attach covalently to microbial cell surfaces
What is a highly reactive thioester bond
Unlike the classical pathway, the lectin pathway functions completely independently of these adaptive immune molecules
What are antibodies?
The rapid cleavage of thousands of native C3 molecules by surface convertases is known as this feedback mechanism
What is amplification loop?
This complement receptor expressed on human erythrocytes binds C3b-coated circulating immune complexes to transport them to the liver and spleen?
What is CR1?
All three complement activation pathways converge on generating C3b and assembling this type of enzyme complex
What is C3 convertase?
Activated C1s proteolytically cleaves these two serum proteins to form the classical C3 convertase
What is C4 and C2?
Active MASP-2 cleaves these two circulating complement proteins
What are C4 and C2?
During strong inflammatory reactions, this blood-clotting cascade enzyme can directly cleave C3 and C5 to activate complement
What is thrombin?
Adding a second C3b molecule to C4b2a or C3bBb converts the molecules into enzymes capable of cleaving what next cascade component
What is C5 (forming C5 convertases)
This pentameric antibody forms a "staple" conformation to allow C1q binding
What is IgM?
In addition to MBL, this family of carbohydrate-binding proteins uses collagen-like domains to recognize acetylated sugars on microbes
What are ficolins?
This fluid-phase alternative pathway mechanism involves continuous low-level spontaneous hydrolysis of C3
What is C3 tickover?
Which complement component initiates the physical assembly of the Membrane Attack Complex (MAC)
What is C5b?