So here I am, dressed up to illustrate innate recognition. If you walked into a bank and found somebody looking like me, you would be a little bit nervous. And that's a really good introduction to the difference between how the innate part of the immune system recognizes threats and how the adaptive part of the immune system recognizes threats. If you see somebody in a bank dressed like that, you don't care who they are. You wouldn't have had to meet them before. You might have never have even set foot in that bank before, and yet you would have a bad feeling. So an entire branch of your immune system works in much the same way. They have a series of what we would call pattern recognition receptors, ways of recognizing a pathogen that are common to a broad group, and don't depend on recognizing any one individual. It's like good solid basic police work. The other one will be the adaptive and after we look at the innate system for a bit, we'll look at the adaptive and then we'll talk about how they get together. >> So an important general strategy for recognizing and destroying pathogens is to look at their overall patterns or properties and recognize them from that. And so, here we see a neutrophil with purple false colored bacteria, and the neutrophil is attaching to the surface of these things, and recognizing their surface properties. Neutrophils are a very important first line of innate defense, they patrol both the circulatory system and the tissues, and they have surface molecules that can identify what we would call bad signs, and then phagocytize the offending pathogens. We also have barriers outside the body. If you think about it, one of the most important problems that we have is things getting in from outside. And so we have a number of defensive molecules that we find in our skin, in our mucosa, in the gut lining and one of the biggest is this enzyme here. This is lysozyme, it's an enzyme that cuts up the cell walls of bacterial, the part that's made up of peptidoglycan, and it snips them. In addition to that later on, we'll be looking at properties of the skin. The skin is also a very good protective barrier and it secretes other compounds in addition to this one. If you're in the bloodstream, god forbid, and a pathogen, one thing that might happen to you is that the complement will construct a pore in your cell surface. This is called a membrane attack complex and it's one of the ways that we have of getting rid of circulating pathogens. So here we have the complement proteins, they're producing a pore, and this means basically that they have punched a hole in the pathogen, it's equilibrating and that's another word for death. Finally, we have a number of pattern recognition molecules that are found in the cytoplasm should things go awry in there. Also we find this particular motif on the surface of neutrophils, and it's a leucine-rich hook domain that's involved in identifying a lot of different molecules that are characteristic of various pathogens, both bacterial and fungal, and other kinds of eukaryotes. So we don't just have one innate response. We have a constellation of innate response, and they all work together. Because these things are already in the ready, that is we don't have to rearrange DNA, we don't have to undergo selection processes to help regulate these things. If a new pathogen arrives, then you will see here in yellow. The innate response will take place pretty much immediately. And so, again, one of the advantages of an innate response is that it's very quick, and it identifies things based on properties that you sort of knew about genetically speaking in advance. Now, we're going to look at the adaptive response and we can see that the adaptive response here shown in blue which includes antibodies and t-cells is something that takes a good week to kick in. So the thing that keeps you alive before these things get going is your innate response, but your adaptive response has a sort of different aspect to it. It's more like what we would have with fingerprinting, DNA fingerprinting, mug shots, facial recognition, text analysis, voice patterns, all of these things are something where you have to have exposure to a bad guy first and then you can mount a very specific response to that. The nice thing about an adaptive response, as we can see here, is that it retains a memory of this pathogen. So you can see the next time we get a repeat of this pathogen, again, the innate system is up and running very quickly. And so is the adaptive and we get a stronger response and we're going to see we get more effective antibodies. So these are both issues we're going to look at in later lectures. We're going to explore the innate system in more detail. We're going to explore the adaptive system in more detail. And here is a reminder that they work together and use two different approaches to save you from the bad guys. Here is a summary table, you're going to see this again but because the innate and adaptive systems work together, it's a sort of a reminder that I'm going to be giving you from time to time about their differences. The innate is fast, the adaptive is slower especially the first time. The innate is always there. The adaptive requires gene rearrangement, and not just gene rearrangement we'll see, but first man and gene rearrangement, and then a selective process. And that's going to take up to two weeks to get up and running. The innate system recognizes molecules, and those are pattern recognition because they're the kinds of molecules the pathogen is going to have that you aren't, and which it can't get by without. That is to say, peptidoglycan walls are nothing like your compounds, and it's something the pathogen can't evolve to make something different. However, if we look at the adaptive, it recognizes very specific parts of proteins. You make proteins, I make proteins, pathogens make proteins. But the adaptive response will recognize specific shapes or parts or amino acid sequences of those proteins. So what we have here is an innate response that involve the white blood cells neutrophils, macrophages, NK cells, also proteins in barriers. All of those things we'll look at in lecture two. And the adaptive response looks at B cells, the production of antibodies and we'll look a brief intro to T cells and Th cells, but they will be the subject of another course in this series.
