The Innate Immune Response: Study with Video Lessons, Practice Problems & Examples

The innate immune response is the body's first line of defense against pathogens, comprising three main components: chemical and physical barriers, cell intrinsic responses, and phagocytic cells. Pathogen-associated molecular patterns (PAMPs) are recognized by pattern recognition receptors like Toll-like receptors (TLRs), triggering immune activation. The complement system, a collection of proteins, aids in pathogen elimination. Natural killer cells induce apoptosis in infected cells, enhancing overall immunity. Inflammation, characterized by pain, heat, and swelling, further supports pathogen clearance and activates the adaptive immune response through dendritic cells.

Innate Immunity

Hi. In this video, I'm going to be talking about the innate immune response. So remember the innate immune response is going to be the first response. It's much more simple. But essentially there are 3 components to the innate immune response. The first are chemical and physical barriers, which I'm not going to talk about because they're just kind of common sense. Right? These are the skin, acidic pH of the gut, sort of enzymes, or proteins in the mucus that can degrade bacteria or harm viruses or, you know, get rid of these pathogens before they can actually infect cells and cause harm. So those kind of make sense. Then we have the second response, and these are the cell intrinsic responses. So these are responses that a single cell can do to stop the pathogen. And then finally, you have phagocytic cells. So these are very similar to cell intrinsic responses because usually phagocytic cells are one cell. But usually there are collections of phagocytic cells which go travel around the body and, you know, can be activated and activate other cells to destroy the pathogen. So here's just an example of a blood sample. So you can see the blood cells here. So these little, sort of, donut-looking things are blood cells, but you see all these other things in the cell as well. And these can be part of the innate immune response. They're phagocytic cells, they're white blood cells, they're things that are coming in recognizing pathogens and stopping the infection. The infection. So what happens after the body is presented with some type of pathogen or infection? So after the infection, there are multiple components that come together to initiate the innate immune system response. So the first thing that's really important in the innate immune system response are these things called pathogen-associated molecular patterns. We abbreviate this as PAMPs. So PAMPs are actually sequences, on the infection itself that the host cell recognizes. So a lot of bacteria, some viruses, they have these things called PAMPs, which are very similar across all of one species of bacteria, all of this one class of virus. So the innate immune response, which is not a very specific response, it's kind of just this all-out response, but it can recognize these PAMPs because they're similar on so many different bacteria. And so the things that recognize these PAMPs are called pattern recognition receptors. So these are on the surface of the innate immune system cells, and they can bind to the PAMPs and they say, okay, here's the pathogen. Because our body doesn't have any PAMPs, so if I experience a PAMP, then it must mean that I'm interacting with the bacteria. So an example of this is called the toll-like receptor, this is the most common example that you'll see. And the toll-like receptor or the TLR, when it can bind to a PAMP, this is going to initiate this innate immune response. So signaling is going to be activated, it's going going to activate cells, cells are going to start phagocytosing things, and the innate immune response is going to be really, like highly upregulated. So once the pathogen once the PAMPs are bound to the receptor, this can stimulate the cell to kill the pathogen. It can activate other cells, and eventually lead actually to the adaptive immune system response. But I'll talk about that more in a second. So here we have an example of a Toll-like receptor, You can see Toll-like receptor, TLR4. So if an antigen, say this bacteria, binds this Toll-like receptor, then this can signal all of a bunch of different downstream pathways in the cell. And all of these pathways are immune system components. They're all going to activate the cell to do something to stop this pathogen, either by, you know, initiating phagocytosis, initiating the release of chemicals that will activate other pathways, or the adaptive immune system. And I'm not going to go into the specifics, so you definitely don't need to memorize these pathways or understand, you know, what these abbreviations are. Just understand that some type of pathogen interacts via the TLR, which is a pattern recognition receptor because of the PAMPs that are present on a lot of different bacteria that activates the cell to do a lot of different things. Now, there are other components of the innate immune system that are in addition to these PAMPs being recognized by things like Toll-like receptors. So this includes the complement system. Now the complement system is a collection of around 20 proteins that just always are circling in the blood. Now, if you get an infection, these proteins then become activated and can help get rid of the pathogen. Now, there's a lot of different nuances with the complement system, but I'm going to save that for your immunology classes. But ju

Which of the following is not an innate immune response?

• A. The skin barrier
• B. Phagocytic cells
• C. Complement system
• D. Antibody production

What is the name of the pathogenic sequence that a host cell recognizes as foreign?

• A. Pattern recognition receptors
• B. PAMPs
• C. Toll-like receptors
• D. Complement sequences

Here’s what students ask on this topic:

What are the main components of the innate immune response?

The innate immune response consists of three main components: chemical and physical barriers, cell intrinsic responses, and phagocytic cells. Chemical and physical barriers include the skin, acidic pH of the gut, and enzymes in mucus that degrade pathogens. Cell intrinsic responses are actions taken by individual cells to stop pathogens, such as producing antiviral proteins. Phagocytic cells, like macrophages and neutrophils, engulf and destroy pathogens. These components work together to provide a rapid, non-specific defense against infections.

How do Toll-like receptors (TLRs) function in the innate immune response?

Toll-like receptors (TLRs) are pattern recognition receptors on the surface of innate immune cells. They recognize pathogen-associated molecular patterns (PAMPs) present on pathogens like bacteria and viruses. When a TLR binds to a PAMP, it triggers a signaling cascade that activates the immune cell. This activation can lead to phagocytosis of the pathogen, release of inflammatory cytokines, and stimulation of other immune pathways. TLRs play a crucial role in initiating the innate immune response and bridging it to the adaptive immune response.

What is the role of the complement system in the innate immune response?

The complement system is a collection of around 20 proteins circulating in the blood that become activated in response to infection. These proteins work together to enhance the ability of antibodies and phagocytic cells to clear pathogens. Activation of the complement system can lead to the formation of a membrane attack complex that lyses pathogens, opsonization to enhance phagocytosis, and the release of inflammatory mediators. The complement system is a key component of the innate immune response, providing a rapid and non-specific defense against pathogens.

What are pathogen-associated molecular patterns (PAMPs) and how are they recognized?

Pathogen-associated molecular patterns (PAMPs) are molecular structures found on the surface of pathogens like bacteria and viruses. These patterns are recognized by pattern recognition receptors (PRRs) on innate immune cells. One common type of PRR is the Toll-like receptor (TLR). When a TLR binds to a PAMP, it triggers an immune response, leading to the activation of immune cells, phagocytosis of the pathogen, and the release of inflammatory cytokines. PAMPs are essential for the innate immune system to quickly identify and respond to infections.

How do natural killer (NK) cells contribute to the innate immune response?

Natural killer (NK) cells are a type of lymphocyte that play a crucial role in the innate immune response. They patrol the body and identify cells infected with viruses or transformed into cancer cells. Upon recognizing an infected or abnormal cell, NK cells induce apoptosis (programmed cell death) in the target cell. This process helps to eliminate the infected cell and the pathogen within it, preventing the spread of infection. NK cells are essential for controlling viral infections and tumor surveillance.