𝐀𝐜𝐭𝐢𝐯𝐚𝐭𝐢𝐨𝐧 𝐎𝐟 𝐂𝐨𝐦𝐩𝐥𝐞𝐦𝐞𝐧𝐭 𝐒𝐲𝐬𝐭𝐞𝐦 𝐈𝐦𝐦𝐮𝐧𝐨𝐥𝐨𝐠𝐲 [𝐇𝐃 𝐀𝐧𝐢𝐦𝐚𝐭𝐢𝐨𝐧 ]

Complement System Overview

What is the Complement System?

• The complement system consists of a group of serum proteins that activate inflammation, destroy cells, and participate in opsonization.

• It can be activated by various foreign molecules, responding in a sequential manner to produce a cascade of reactions.

Activation Pathways

Classical Pathway

• The classical pathway begins when C1 becomes activated upon binding to an antigen-antibody complex. This activation leads to the cleavage of C2 into C2a and C2b, as well as C4 into C4a and C4b.

Alternative Pathway

• In the alternative pathway, antigens such as endotoxins or polysaccharides react with C3b. Small amounts of C3a and C3b are constantly formed from C3 but are usually destroyed without activation.

• Factor B, Factor D, and properdin interact with C3b to form a complex called c3 convertase which cleaves more C3 into additional C3a and C3b.

Role of Cleaved Components

• After cleavage of C3:

• C3a: Involved in stimulating inflammation.