Complement

Complement

This is a system of about 20 proteins found in the blood and tissues. It gets activated by immune complexes - an antigen and an antibody joined together, and by foreign sugars on bacterial cell walls.

(One type is the Membrane Attack Complex; five proteins which join together and make holes in bacteria)

Action

There are lots of different types each working in a different way:

• Embed in the bacterial plasma membrane and make holes, so it leaks, and salts and water enter, destroying the inner environment and killing the microbe.
• Binds to membrane, stimulating phagocytosis from other cells. This is acting as an opsonin.
• Acts as a chemotaxin, attracting phagocytic cells like neutrophils to the area.