So now that we know what the structure of the antibody looks like, let's discuss what the mechanism is by which the antibody actually elicits a defensive response by our immune system. So antibodies can either be found bound onto the membrane of immune cells or they can float around as free antibodies within the blood or lymph of our body. And either way, when the antibody locates and binds onto that specific antigen for which it was actually built for, they form the antibody antigen complex. And once the complex forms, it elicits some type of response that begins a defensive mechanism to kill off that particular pathogen. Now, what type of mechanism do we actually have? Well, we have three important types of mechanisms that we're going to focus on in this lecture.