Innate Immunity - Video Tutorials & Practice Problems
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Innate Immune Response
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5m
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Hi. In this video, we'll be talking about the innate immune system, your body's first line of defense against pathogens. Now, the innate immune system is going to mount a non specific response and that's opposed to as opposed to the specific response that the adaptive immune system will launch. The skin is basically the front lines of your body's defense systems. It's sort of like the moat to the fortress and it's going to protect the inside of your body from any pathogens that might want to enter. Of course, it's an imperfect barrier. Not only are there holes in it, like you can see this nostril right here, but it can be penetrated in other ways, it can be broken open through physical injury, allow allowing pathogens in, so it's the front line but very much so not the final line of defense. Now, all of the, openings to your body will generally have some mucus surrounding its purpose is to trap foreign invaders. So, you know, we have mucus in our nostrils because that's an opening to the outside, we could potentially breathe in pathogens like you see happening here in this image, so the, goal is that if we do breathe in some bad stuff, it's just going to get stuck in our mucus and then we will expel it like you see this guy doing here. It's worth noting that mucus also can contain antimicrobial enzymes. So, not only will it trap those invaders, but it might actually kill them while they're trapped. Kind Like a roach motel. You know, the pathogens check-in but they don't check out. Now, you will also find what are called lysozymes, which are enzymes that break down bacterial cell walls and you'll find these associated with tissues that, you know, can have, pathogens entering from the outside. So it's just another sort of non specific defense, in these vulnerable areas of the body. Now, the innate immune response is going to be that first response to pathogens, it's going to be initiated by leukocytes which are those white blood cells and, again, it's going to be nonspecific as opposed to the specificity of the adaptive immune system. Now, since it's non, even though it's nonspecific, the immune cells have to be able to recognize the pathogens and they're gonna do that through what are called Pathogen Associated Molecular Patterns or PAMPs and basically, these are just, molecules that are commonly displayed by pathogens and will not be displayed by human cells or, you know, cells of the organism's body so that it knows they're foreign. Perfect example of this is the lipopolysaccharides that you find on the surface of bacterial cells. You can see one right behind my head here and, basically, this is going to be, just one of those pathogen associated molecular patterns, not super specific, you know, like lots of different types of bacteria are going to have these but it's a way to tip our immune system off that, hey, there's some bacteria hanging out here. So, how does our immune system recognize it? Well, our immune cells will have what are called pattern recognition receptors that are membrane receptors that identify those pants. So these PRRs are going to identify the PAMPs and a specific type of pattern recognition receptor that you will see in a lot of immune cells are these Toll like receptors as as they're called, or TLRs and, again, those are a type of pattern recognition receptor that are found on some immune cells and what's special about them is they will initiate a signaling cascade, which will help recruit other immune cells and lead to a mounted immune response. One specific type of Toll like receptor, those, lipopolysaccharides from bacteria, those PAMPs that bacteria have. And it will release cytokines in response to binding with the lipopolysaccharide and those cytokines are signaling molecules that will attract other immune cells and help mount the immune response and you can see those TLRs right here, this is our cell membrane, they are protruding out from the cell surface bind that lipopolysaccharide that is expressed by bacteria and that binding, as you can hope, is by bacteria and that binding, as you can hopefully see, will initiate, you know, a whole cascade of responses responses within the cell that ultimately will lead to, for example, releasing those cytokines. With that, let's flip the page.
2
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Innate Immune Cells
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6m
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One of the main weapons that the cells of the innate immune system have against pathogens is phagocytosis. It allows them to, remove these pathogens and prevent them, hopefully, hopefully, from infecting any cells. Now, there are gonna be 3 types of cells that will be performing phagocytosis in the innate immune system. Those are neutrophils which are phagocytes or cells that perform phagocytosis that will circulate in the blood and they're going to be attracted to infected tissues by cytokines, those messengers, or those, messenger molecules, those chemical signals that will attract cells of the immune system. So, if I jump out of the way here, you can see a neutrophil circulating in the blood, you know, here we have a red, oops, A red blood cell. And it's gonna circulate in the blood and look for these cytokines. And it's going to be attracted to them. Go in. Look for those pathogens that you can see here. So, that's a pathogen and it's going to phagocytose them. It's gonna eat them up. And you can see what that phagocytosis kind of looks like here. The cell will actually pinch its membrane around the thing it's trying to engulf and basically suck it in in a vesicle. And here in this particular, cell, it's actually going to digest what it, takes in and break it down like you see there. Now, neutrophils are kinda like the mobile warriors. They're gonna go seek and destroy these pathogens but macrophages are more like defenders. They kind of hang out in tissues and organs that will frequently encounter pathogens, and they'll mainly be found around like the lymphatic system and especially lymph nodes because, you know, there are gonna be a lot of pathogens that cycle through there. And, in addition to macrophages, you'll find dendritic cells in those areas too. And these dendritic cells, are also phagocytes except their job is a little different. Gobble, you know, the pathogen they find like, for example, the macrophages. Its job is just to gobble up, any pathogen it finds so like here's a bacteria it's going to gobble it up, remove it. Dendritic cells are there to actually take what they, phagocytose and use it to stimulate the adaptive immune system. So, their job is super important because they're going to bridge the innate immune system and the adaptive immune system and they're going to help trigger an adaptive immune response. So, these phagocytes are not the only innate immune responses our body has, some other tactics they can use. You might not think of it because, you know, we tend not to deal with this in our day to day anymore but, you know, we used to have to worry about parasites much more often. We actually have these immune cells called eosinophils that are there to defend against multicellular parasites And we also have some defenses against viruses. There are these cells called natural killer cells, cell death. And, if I jump out of the way here, you can see, the cells of our body will basically present certain things on their cell surface that allow our immune system to identify them as self, as as part of the organism so, you know, like don't hurt these guys, these are the good guys. So here we have a natural killer cell and it it's checking out this guy and basically saying, okay. You're alright. Here, we have a cell infected with a virus and that is going to be terminated by this natural killer cell. It's gonna trigger apoptosis and cause that cell to lyse or break apart and it's going to do this because it's going to be able to detect whether or not the virus is in there, in a system that we're actually gonna cover when we talk about adaptive immunity so I'm not gonna, really get into the details now. Needless to say, these natural killer cells can identify cells that are infected with viruses and will destroy them. Now, our cells will also secrete these special cytokines called interferons and these will actually induce induce cells to interfere with viral replication in various ways. Now, lastly I wanna talk about, this basically system of proteins called the complement system. These proteins will be found in the blood and they're activated by those pathogen associated molecular patterns. They're also activated by antibodies and to the innate immune system. However, they are part of the innate immune system. I just want to point out that they're not exclusive to the innate immune system. However, they are part of the innate immune system because they can recognize those pathogen associated molecular patterns and what they're gonna do is basically, put holes in the membranes of these pathogens and cause the cells to lyse. And you can see the complement proteins here. Basically, they'll form a pore that will, stick through the membrane of the pathogen and, you know, cause it to break open, you know, you'll have a bunch of these pores forming in the membrane of the pathogen and it will just explode like you see going on here. With that, let's flip the page.
3
concept
Inflammatory Response
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3m
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The inflammatory response is a special type of innate immune response that will result in swelling of a region. So, if for example you, you know, fall and scrape your knee, let's say. Following that injury, platelets are going to form clots to seal off that site and prevent blood loss and also hopefully prevent any nasty stuff from getting into the wound. Now, those wounded tissues and the macrophages around them are gonna release chemokines which are basically like a special type of cytokine that recruits cells to the infection site. Now, mast cells, which are a special type of immune cell, they're a type of granulocyte, Their main job, or one of their main jobs, is to release histamine and this is a chemical signal that's going to constrict blood vessels in the area and that's going to constrict blood vessels in the area and that's going to not only reduce blood flow to the area but also prevent blood loss from the area. And part of, part of Mast Cell's job is also to signal the peripheral blood vessels to the infection site. So, you know, the local blood vessels are gonna constrict. The blood vessels in the area around that are actually going to dilate and that combination of dilation and the chemokines that are being secreted is a major signal to neutrophils to like mobilize, get there right away, and go to that infection immunosuppression site and release cytokines to recruit more immune cells. So, hopefully, you can see that immune responses are sort of like, escalations, You know, there's an initial signal of like help, bunch of immune cells move in and, you know, they kind of shout help and more guys come in and the the signals and the response grows and grows. It's an escalation to recruit more and more, cells to that area to deal with any pathogens or any infection and, here I'm trying to sort of cheat and use the same figure but pretend that this time, you know, these are histamines and also cytokines and stuff. Don't have a great image unfortunately to illustrate the inflammatory response but it's a very similar process and and this is really a theme you'll see throughout the immune system is cells secreting a signal to recruit other cells to that area to mount some type of immune defense. So that's all I have for this video. I'll see you guys next time. Stay healthy.