dr. anthony fauci, head of the national institute of allergy and infectious diseases. welcome back, dr. fauci. so before we get into the details in general terms this is about how the body fights disease. >> indeed. what the laureates established and discovered was the precise mechanisms whereby the two components of the immune system are activated. the very primitive, inate immune system which was what beutler and hoffman discoverd. and then the connection between that inate immune system and what we call the adaptive immune system which is much more sophisticated part of our immune system which is what ralph steinman was able to delineate by discovering this very specialized cell so it is really a very worthy discovery of the nobel prize. >> brown: start with a little bit more on the inate i am unity. this is described as the first line of defense. what that is that mean. >> a very primitive line of defense. it's what very, very early primitive animals have who have not yet involved into developing what we call an ataptive immune system. it instantaneously senses invaders like bacteri