Okay. Here we go. The course presents the dangers of a misdirected adaptive immune system, sad really, because your adaptive immune system is your best defender, and moreover, it has a bunch of safeguards to prevent it from turning on you. These safeguards are collectively referred to as immune tolerance. Now, as a first step, I want to review and extend some information from the lecture on inflammation, because these are the processes that turn on the adaptive immune system, and that's whether it's directed a real threat or a bunch of harmless pollen, or heaven forfend your brand new kidney transplant. So what are these fundamental danger triggers? They're generally things that indicate a cell is damaged or dying or that a really nasty predator has turned up inside the body. In this section, we're going to look at some specific triggers and then two major examples of how the body responds to these specific triggers. This certainly doesn't exhaust all the possibilities that would be the triggers or responses, but it should give you some idea of how the system works. The first thing we're going to look at is the DAMPS, that is the death or damage associated molecules and then we'll look at the PAMPS, the pattern associated molecules. Here we have a really interesting and probably one of the most deadly environmental triggers of a DAMPS response, and that is asbestos fibers. This is an electron micrograph and it gives you a really good feel for which is why these things might be a nasty thing to have in your lungs. It's definitely an irritant and can lead to cancer. There are plenty of other environmental irritants that will raise an immune response and will not necessarily give you long term damage. One of these is alum and here's a really pretty alum crystal. We'll see that alum and various aluminum salts are used as activators of the very NOD receptors we're going to use to activate the inflammasome, and thus the innate and adaptive response. It's something that's used as an adjuvant to vaccines, and that's where it works in much the same way, it raises the immune response and improves the effectiveness of the vaccine that you're delivering. So, this is not remotely the same thing as asbestos, it's really something of a good thing. Something that's definitely a bad thing is UV damage, and here we have a picture of the sun with a spectacular corona, emitting UV light, and UV light will prompt a danger response. This is because ultraviolet lights, specifically damages the DNA, and here we have a picture where an incoming photon, is damaging the DNA and causing the cell to either undergo apoptosis or if it's bad enough, it can kill it outright. Another thing that is a bad sign is something that should be inside the cell, and you find it outside the cell, that's a signal that perhaps the cell is leaking, and has some other kind of problem, because remember when we do apoptosis, the cell sort of partitions itself off, without leaking things outside the plasma membrane. In particular, if you'll recall in apoptosis, we even partitioned the nucleus. So, here is a picture of DNA wrapped around histones, and if you find this step outside the cell, that's considered a really bad sign. Also, other things like transcription factors and other molecules that are supposed to be inside the nucleus, find them outside, you respond to it. Even things that should be in the cytoplasm, if they make their way outside, it's considered a bad sign. Other kinds of molecules also will break up and indicate damage. Here is beta amyloid, which is produced by clipping a beta amyloid precursor. This is a protein that can build up inside your brain and, then seems to set off a train of events eventually leading to Alzheimer's. They can actually turn some of this stuff over, especially if you're asleep. But, in general, if this begins to build up, its not considered a good sign and the inflammatory response may lead to further damage in the brain. Other various chemicals that should be inside the cell include things like ATP. ATP is a good thing but you don't leave it hanging around outside the cell, it's much too precious. If you see the stuff outside the cell, that's a sign that the cell is leaking and that means that the cell is not very healthy at all. Even things like too much glucose, crystals of cholesterol, uric, that is uric acid, and even fragments of [inaudible]. Now, [inaudible] is an extracellular matrix glycoprotein, and that's something that shouldn't, you might say, hey, it's supposed to be outside yourself. Well, yes. But it's not supposed to be outside the snuff cell in small fragments, and if small fragments had broken off of the extracellular matrix, that's another sign that things are not going well. So, if you think about something that you would get, if a cell is broken up or damaged or under attack, there's probably some molecule that's capable of responding to that. Now, the next thing we need to look at, are the pattern recognition danger receptors. The biggest category of these things are designed to recognize bacteria which are always out there and try to make a meal of you. This is the gram negative bacterial cell wall in the middle, surrounded by two membranes, an inner plasma membrane, the maval, then an outer membrane and these are really something that cause a lot of pain and suffering, in humans. We're running out of antibiotics to treat these things and so, supporting the immune system in getting rid of them is going to be, again, a critical way to keep people alive and healthy. Now, if you'll notice, we have with a polysaccharide on the outside, we have the peptidoglycan wall. This particular diagram does not show the bacterial flagella, but all of those compounds have toll-like receptors that will recognize their presence and set off a signal, it's one of the signals we're about to look at. Obvious, it's also a reminder there are toll-like receptors again for other pathogens, types of pathogens besides bacteria, including fungi and cell surface materials found in other eukaryotic pathogens. The NOD receptor and it's a specific non receptor NLR, and it has a leucine rich hook. NLR is again a cytoplasmic receptor and this is one that will essentially trigger and become part of the implant zone. Now, here is a TLR leucine rich hook detail, and really we find that same structure also in the NOD hook receptor, and this is a leucine rich recognition region that is a part of many innate recognition molecules. On the right side, you can see that the toll-like receptor, is embedded in the membrane and does, in this case, it's exterior part is recognizing a lipopolysaccharide. There are also versions of this, that the exterior part will extend into the lumen of the endoplasmic reticulum. But unlike the previous example, where the whole thing was part of in the cytoplasm, in this case the toll-like receptor spans the membrane and will receive a recognition stimulus on one side, and will produce a signal to the inside, that will have up-regulate toll-like consequences, which again we're about to look at. So, again, we have two innate recognition systems, one in the cytoplasm and one embedded in the membranes, either sensing things outside the cell or things that had been recently phagocytized. The cytoplasmic version is going to lead to the production of IL-1, a very fundamental cytokine, that is important in up-regulating the immune response throughout the body. So, this guy here is, in some ways, in the signaling sense, the start of it all and it is going to be activated as a consequence of the activation of the NOD NLR. That happens when the danger signal activates the NLR by changing its conformation. The change in the conformation is going to lead to the attachment of the ASC, which has a card domain, which is important in assembling big structures. Here, we can see that we put together a heptamer of NOD NLRs with card domains, and those card domains are going to further cause the association of a caspase, that's seen over here, and the assembly of this complex structure called an inflammasome. The center of the inflammasome has the hydrolytic domains of the caspase, and that's going to take the IL-1 precursor, clip it, and cause it to activate. When it activates, it's going to enter a secretory vesicle and then get secreted to the outside. So interestingly enough, this structure is assembled in the cytoplasm, activates a cytoplasmic precursor, that's eventually going to be secreted to the outside of the cell, and then do a very general up-regulation of the inflammatory response throughout the body. Now, the other one we want to look at, is the activation of the NF-kappaB. NF-kappaB is a transcription factor, that is, it binds to the DNA as shown here. Of course, as a transcription factor, it binds to specific parts of the DNA, and those specific parts are the upper regulatory parts of genes that produce more inflammatory cytokines, molecules that allow cells to recognize other kinds of threats. So, this system is one in which we take a precursor in the cytoplasm, activate it and send it into the nucleus to up-regulate genes, and we will see this in the animation to follow. So, here, we have the NF-kappaB in its inhibited situation. You can see that it's held up here near the plasma membrane by the anchoring domains, which are attached to the spectrin proteins, that form a mesh work directly underneath the plasma membrane. The mesh work is held at its nodes by these tropomyosin molecules, which are also attached to the actin of the cytoskeleton. So, here, we have the transcription factor ready to go, and what we need to do is detach it and bring it into the nucleus through the pore here. So, the first thing that we're going to do is get a signal from something like a toll-like receptor, that will activate a phosphorylate series, and we'll see that we will phosphorylate the inhibitor. When we do that, the inhibitor leaves through the dimer here, it will then pick up a ubiquitin, and that will target it to the proteasome, where it will enter and get degraded. Now, as soon as that inhibitor leaves, we have a conformational change in the NF-kappaB, and it will open up and the anchoring repeats will let go of the spectrum. When they do that, then we will get a translocation of the NF-kappaB through the pore and into the nucleus. Thus, the NF-kappaB.
