T Dependent & T Independent Antigens - Video Tutorials & Practice Problems
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1
concept
T Dependent & T Independent Antigens
Video duration:
2m
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in this video we're going to begin our lesson on T dependent antigens and t independent antigens. And so it turns out that the mechanism of B cell activation actually depends on the type of antigen that that B cell encounters. And so when it comes to B cell activation really there are two types of antigens that we need to introduce. And so the first type of antigen is going to be called T dependent antigens. And the second type of antigens are called T independent antigens. Now the T dependent antigens as their name implies, these are going to be antigens that depend on or in other words require helper T cells or T. H cells in order for the activation of naive B cells. Now on the other hand the t independent antigens as their name implies are going to be antigens that are capable of activating naive B cells independent of or in other words without helper T cells or th cells. And so really what we're saying here is that T dependent antigens depend on helper T cells in order for a B cell to become activated. And again t independent antigens do not require helper T cells. They are able to activate B cells independent of or without helper T cells. Now it turns out that most of the antigens are going to be T dependent antigens. And so moving forward we're going to focus on those first. But as we move forward in their own separate videos we will talk more details about T dependent antigens and the activation of B cells via T dependent antigens as well as the activation of B cells via t independent antigens. And so I'll see you all in our next video.
2
concept
B Cell Activation by T Dependent Antigens
Video duration:
5m
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in this video we're going to begin our lesson on B cell activation by T dependent antigens. And so first we need to recall from some of our previous lesson videos that naive B cells or inactive B cells can be activated by helper T cells or th cells. And so the activation of a naive B cell via T dependent antigens actually occurs via a series of five steps that you can see in our image down below and are numbered one through five. And so over here on the far left of our image we have the very first step of T dependent antigen B cell activation. And so notice that we're showing you an image over here of a naive B cell or an inactive B cell. And of course the B cell on its surface is going to have thousands of identical B cell receptors or B. C. R. S. And so here what we're saying in the first step is that the B cell receptor or the B. C. R. Is going to bind the free antigen or the free floating antigen. And so you can see the antigen here is in red and you can see that RbC are here is binding to that free antigen. Now once the antigen has been bound by the B. C. R. And the second step the B cell is then going to process the antigen, it's going to process the antigen into smaller fragments. And so in order to do that the antigen needs to be internalized inside of the B cell. And then it will be fragmented and broken down into smaller pieces, smaller fragments. Then in the third step the B cell is then going to present those antigen fragments on its surface on MHC Class two molecules which recall are on the surface of the cell. And so notice down below were indicating that the MHC Class two molecule is going to look like this in our image and notice that these MHC s are presenting the smaller fragments of the antigen that was internalized and processed. And recall from our previous lesson videos that these MHC ESx or major historic compatibility complexes uh specifically class to when antigens are presented on MHC Class two. It's the helper T cells that can recognize those presented antigens. And so in step number four which you'll notice is that the helper T cell or the th cell Is going to recognize those antigens that are presented on the MHC Class two. And so the helper T cell will go on to activate the naive be so and so notice over here we have our helper T cell in our image our th cell and of course the helper T cell has those cd four molecules on it. It's also known as the Cd four cell and it has T cell receptors that only detect presented antigens. Uh and so ah the T cell receptors of helper T cells will only detect presented antigens on MHC Class two molecules. And so notice the interaction here is the T. C. R. Is recognizing the antigen presented on the MHC Class two. And so that will allow the helper T cell to release a series of side Akins or communicating signals or molecules. And those cytokines released by the helper T cell will be able to affect the B cell in such a way that it will activate that naive B cell. And of course we know from our previous lesson videos that activated B cells will go on to differentiate into either plasma cells that secrete antibodies or differentiate into memory B cells. That will be important for a secondary future infection. And so notice down below we're showing you the plasma cells over here on the left side creating these antibodies and the memory B cell over here on the right and so ultimately what we've seen is that T dependent antigens depend on helper T cells in order to activate the B cells. And so this here is going to be the key feature of T dependent antigens. The fact that they depend on helper T cells. And again this will be different when we talk about t independent antigens as we move forward in our course. But for now this year concludes our brief lesson on B cell activation by T dependent antigens. And we'll be able to get some practice moving forward. So I'll see you all in our next video
3
Problem
Problem
Which of the following is a step required for activation of a B cell by a T-dependent antigen?
A
The antigen is presented on MHC class I proteins of the T cell.
B
The antigen binds to the BCR of a naive B cell.
C
The antigen is presented on MHC class II proteins of the B cell.
D
TH cell recognizes the antigen as a pathogen and triggers apoptosis in the B cell.
E
TH cell recognizes the antigen as a pathogen and activates the B cell causing the B cell to secrete antibodies.
F
B, C, & E.
G
A, B & E.
4
Problem
Problem
T-dependent antigens can stimulate B cells to become activated but require _________ assistance.
A
Interleukin.
B
Cytokine.
C
Interferon.
D
Antibody.
5
concept
B Cell Activation by T Independent Antigens
Video duration:
3m
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in this video we're going to talk more details about B cell activation by T independent antigens. And so first we need to recall from some of our previous lesson videos that unlike T dependent antigens, T independent antigens can actually activate naive B cells independent of helper T cells. Or in other words without helper T cells. Now these T independent antigens are typically long policy Sacha rides with multiple closely spaced identical repeating subunits. And also these T independent antigens. They typically do not initiate an immune response and very young Children which typically makes very young Children and kids more susceptible to some pathogens that have these t independent antigens. Now the good thing is is that these t independent antigens are not as common as T dependent antigens. And so if we take a look at our image down below we can get a better understanding of these t independent antigenics. And so what you'll notice is on the left hand side of our image over here we have our naive B cell in blue which of course is going to have its B. Cell receptors on its surface. It's B. C. R. S. And notice that here in red this long structure that you see right here represents our T independent antigen. And again these t independent antigens typically are going to be long policy Sacha rides with multiple closely spaced, identical repeating subunits and that's what we see here is these multiple, closely spaced identical repeating subunits throughout this entire uh T T. T. Independent antigens. And so these t independent antigens are able to activate this naive B Cell without a helper T. Cell. And so notice that there is no helper T cell anywhere within this image. And so B cell activation can still occur with these T. Independent antigens. And so of course the NAIVE B cell when it becomes activated it can proliferate or multiply and differentiate either into plasma cells that secrete antibodies or memory B cells that are important for protecting upon a future infection. And so really the key here is that T dependent antigens require helper T cells, whereas T independent antigens do not require helper T cells to activate a B. Cell. And so this here concludes our brief lesson on B cell activation by T independent antigens. And we'll be able to get some practice applying these concepts moving forward. So I'll see you all in our next video.
6
Problem
Problem
T-independent antigens:
A
Interact with MHC I molecules.
B
Require the involvement of T cells.
C
Include pathogen associated polysaccharides.
D
Are usually pathogen associated nucleic acids.
7
Problem
Problem
Lipopolysaccharide (LPS) is an endotoxin found on the surface of gram-negative bacteria. LPS can cause the body to enter septic shock and result in multi-system organ failure. Because of its severe effects, it is important that the immune cells react quickly to LPS. LPS is an antigen that can directly trigger antibody secretion once it comes in contact with a B cell. LPS is what kind of antigen?
