Complement Cascade

Complement Cascade /

A critical component of the innate immune system involving proteolytic cascades to defend against pathogens and enhance immune responses.

Classical Pathway

Initiated by C1 complex binding to antibodies, leading to the formation of C3 and C5 convertases and key effector molecules like C3b and C5a.

Lectin Pathway

Triggered by lectin binding to pathogen surfaces, activating MASP-1 and MASP-2 to cleave C4 and C2, similar to the classical pathway.

Alternative Pathway

Uniquely continuously activated at low levels, involving C3 hydrolysis, factor B and D, properdin, and an amplification loop to enhance the cascade.

Complement Inhibitors

Eculizumab blocks C5 to prevent MAC formation, used in treating conditions like aHUS and PNH; Avacopan is an oral C5 inhibitor trialed in ANCA-associated vasculitis.

Complement Regulation

Involves proteins like factor H, factor I, and MCP to deactivate complement components and prevent excessive activation, crucial for host tissue protection.

Complement and Adaptive Immunity

Complement receptors on B cells enhance immune responses, while complement influences T cell responses, promoting a robust adaptive immune response.