On the other hand, the classical pathway actually needs these antibody antigen complexes to actually take place. Now, the final component I'd like to talk about is how do we actually regulate the complement system? So we don't always want the complement system to actually be activated because it's very, very energy consuming. And so if we don't have any types of pathogens in our body, why would we want the complement system to be activated? Well, we don't. And the way that we regulate it by using many different types of proteins, for example, three proteins that are commonly used by the body to basically regulate and deactivate some of these agents are the following three proteins.