Complement Regulatory Proteins

Seerum Protein P (Properdin)

stabilizes the alternate C3 convertase (alternative pathway) at the pathogen surface

Serum Proteins H & I

factor H recruits I (a protease), which cleaves and inactivates C3b, turning down the complement cascade at the pathogen surface; factor H binds to sialic acids of the body cell surface glycoproteins and recruits I, which protects body cells from actions of C3b

Membrane Protein DAF (decay accelerating factor)

accelerates the dissociation of C4b2b (no C3 convertase of classical pathway) and inhibits the alternative C3 convertase (alternative pathway)

Membrane Cofactor Protein (MCP, CD46)

recruits I to body cell surfaces to breakdown any C3b, protecting body cells from the actions of C3b

Serum Protein C1 Inhibitor (C1INH)

induces dissociation and inhibition of C1 protease C1rC1s; serine protease inhibitor

Serum Protein S (clusterin) and Factor J

prevents C7 from binding to C5b at body cell surfaces, preventing the start of pore formation

Membrane Protein CD59 (protectin)

binds C5b678 on body cells, blocks binding of C9 and MAC formation

Membrane Protein HRF (homologous resistance factor)

binds C5b678 on body cells, blocking binding of C9 and MAC formation