dr. steinman. the intriguing idea that sort of hit me is that the immune system develops a kind of memory to deal with specific attacks. you said this is more complicated. explain. >> well, what it is is that for the early response, it's very non-specific but the adaptive immune system is much more complicated one. it has memory and what we call specificity. it will specifically recognize something, and it will remember the next time you get exposed to that. so it gives a much more robust response. what ralph steinman discovered was the particular type of cell called dendritic cell which bridges the gap between the two immune system by picking up viruss or bacteria or other antigens, even tumor cells and presenting those cells, those products to the immune system that specifically recognizes it. so it's kind of a carrier cell that is able to take whatever it is that you want to respond to and present it in a very specific way to the specific or adaptive immune system. >> brown: so how do these brea