Our immune system consists of two divisions. We have the innate immune system which we're going to focus on in this lecture and we have the quiet or adaptive immune system which we're going to focus on in the next lecture. So, what exactly is the innate immune system? Well, the innate immune system consists of many nonspecific defense mechanisms that begin to act immediately after infection takes place. And what that means is the innate immune system is the primary line of defense against these invading pathogens. That is, the innate immune system acts way before the choir immune system which usually takes several days to actually act as we'll see in the next lecture.