What is the membrane attack complex?

The membrane attack complex (MAC) is a group of proteins that form pores in the cell membranes of target cells, leading to cell lysis and death. It is a key component of the immune system's defense against pathogens, particularly bacteria. The MAC is formed when a series of proteins, including C5b, C6, C7, C8, and C9, come together to create a pore in the target cell's membrane, allowing for the influx of ions and water and ultimately leading to cell death.