The Cytolytic Terminal Complement Complex, also known as the Membrane Attack Complex (MAC), is a complex formed during the terminal stage of the complement cascade, a crucial component of the immune system. Complement refers to a group of proteins circulating in the bloodstream that aid in the body's defense against pathogens.
The Cytolytic Terminal Complement Complex is formed when sequential activation of complement proteins leads to the assembly of a multi-protein complex on the surface of target cells. It is primarily composed of complement proteins C5b, C6, C7, C8, and multiple copies of C9. Once formed, the complex forms pores on the target cell's membrane, leading to cell lysis or destruction.
The assembly of the Cytolytic Terminal Complement Complex begins when complement protein C5 is cleaved by an enzyme called C5 convertase. This initiates a series of enzymatic reactions, eventually resulting in the attachment of C5b to the target cell's surface. As the assembly progresses, C6 and C7 attach to C5b, and then C8 helps anchor the complex further to the target cell membrane. Finally, multiple copies of C9 polymerize and embed into the target cell membrane, forming large pores.
The formation of these pores disrupts the cell membrane's integrity, leading to cell lysis, intracellular content leakage, and ultimately the destruction of the target cell. The Cytolytic Terminal Complement Complex plays a vital role in the immune response by eliminating pathogenic cells, such as bacteria, infected cells, or cancer cells, and preventing their replication or spread in the body.
