Well, C three b has two different functions. One of its function is to act as a molecule known as obsonin. Now, what Opsinin does is it carries out a process known as obsonization. And that basically means it stimulates phagocytic cells of our immune system. It calls upon these phagocytic cells. So C three B goes on and binds onto a special glycoprotein found on the membrane of that particular pathogenic cell.