We've been through this whole section on innate immunity. The next thing that we're going to be looking at is antibodies, and eventually, T-cells. So, we'll be looking at adaptive immunity. So, just before we head on into that, I'd like to do a quick compare and contrast. So, here we are in section five, and we're going to compare and contrast the innate response and the adaptive response. So, both of these are responses that a cell uses to fight off pathogens. They both involve recognizing what is self and what is not self. Again, they both involve the mounting a response against that, and we'll see the adaptive response also upregulates inflammatory responses as well. So, in addition to all of this, we'll see that they communicate with each other. Now, the innate response is found in all organisms. The adaptive response is found in fish, amphibians, reptiles, birds, and mammals. I would like to say, parenthetically, at this point, is that it doesn't work the same way in all of these guys. They have evolved, again, their own special tricks and ways of doing things. But in general, in all of these, we're going to find compounds that are produced from rearranged genes. So, these guys rearrange genes. Innate responses require no rearrangement. Innate responses in general exploit patterns of vulnerability. So, then, when we look at TLRs, we're going to look at things that recognize the general pattern of a molecule that's common to a class of pathogens. Like most bacteria have bacterial cell walls with a particular flagellar protein, we do that. We look at things that recognize certain peptidoglycans and things that recognize certain bacterial lipids. Now, you might want to ask yourself, how come these bacteria, again, don't just change them? Because in their form, they're essential to their function so that when we look at the specific recognition that we employ when we look at adaptive responses, we're looking at something that in many or most cases, involved a very specific sequence of amino acids that produces a very specific shape. So, in this case, a virus or a bacterium can change the details of a protein and essentially, fool the system. So, these two systems have to work together. The other important element to remember is that this thing is ever ready. You are born with these. You can upregulate them. But from day one, if you get a cold or a flu, these will recognize aspects of that flu and begin to fight it off. That's a good thing because if it's a new version of the flu, it's going to take two weeks before your adaptive system is ready to go to work on it. You could be dead by then, in fact, often are, which is why we give you vaccinations, because if you have a previous exposure to something, you can begin to make antibodies and T-cell recognition molecules within three days. So, in this case, when we're looking at adaptive responses, it's quick, it recognizes patterns, and it's Johnny on the spot. Now, you might want to say, well, why wasn't that enough? Well, because in many cases, the pathogens are too fast or they do have ways around it. If you have an infection that hangs on, you may need an adaptive response, an additional layer of second round protection, something that actually helps a lot of your innate responses to do their thing. So, as we go through the rest of this course, there will be times when we are talking specifically about adaptive responses, making antibodies, but we will also see that those antibodies can help the innate responses in particular. They'll help phagocytosis of neutrophils and macrophages. If we're looking at the innate responses, we will see that they often help regulate the adaptive so that if, for example, we have innate recognition of bacteria as opposed to, say, worms, using toll-like receptors, macrophages will pass that information on as well to T-cells, and they will tell B-cells, we'll see to make the right kind of antibody. Now, that's the next lecture that we're going to do. We're going to look at specific classes and categories of antibodies, and just bear in mind that the information that tells you which one of these things to make often comes from innate input that you had at the onset of the infection