20. Adaptive Immunity
Natural Killer Cells
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Natural Killer Cells
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in this video, we're going to begin our lesson on natural killer cells. And so first we need to recall from some of our previous lesson videos that natural killer cells are commonly abbreviated as N. K. S. And these natural killer cells are lymphocytes just like the T cells and the B cells that we've been talking about so far. However, unlike the B cells and T cells that we've talked about so far, which are part of adaptive immunity, these natural killer cells are not considered part of adaptive immunity. And this is because these natural killer cells lack specificity in antigen recognition. And so these natural killer cells are considered part of innate immunity and they're referred to as innate lymphoid cells. Now the role of these natural killer cells is to destroy infected host cells by recognizing irregular patterns on the host cell surface. Now these natural killer cells when they do recognize these irregular patterns on infected host cells, they release these death packages that include molecules such as poor foreign, which creates pores in the membrane and the cell envelope of the uh infected host. So, and it also releases other protea aces, uh proteus containing Granules and those protea aces have are basically enzymes that destroy proteins. And so collectively these death packages released by the natural killer cells can induce a pop ketosis and the infected host cell. Now the natural killer cell can actually recognize one of two irregular patterns on the infected host cell. The first irregular pattern that it can recognize is the lack of MHC Class one on the surface of the infected host cell. And so the lack of MHC class one can actually be a result of some viruses. So some viruses have evolved complex mechanisms that allow them to basically interfere with antigen presentation. And so when it does that these infected cells will not have MHC s on their surface. And so these natural killer cells are able to respond to cells that lack MHC Class one on their surface. And so notice that in this image down below, we're showing you how natural killer cells can induce apoptosis and cells that lack MHC molecules. And so notice over here on the left hand side, we're showing you a virus infecting the host cell and this particular virus again has evolved mechanisms to interfere with antigen presentation. And so notice that whereas the original cell had MHC one on its surface, The infected cell no longer has MHC one. So, the virus is preventing the cell from displaying MHC one MHC Class one molecule. So notice it does not have those molecules on its surface anymore. Now, what this means is without the MHC s, the T cells will not be able to respond. However, the natural killer cell is able to respond um and essentially eliminate cells that do not have MHC on their surface. So the natural killer cell, which is this pink cell over here on the right hand side comes along and it recognizes the lack of MHC s and it will release death packages that include the perforation to basically create pores in the membrane and also proteus containing Granules. And of course the proteus is going to include enzymes that break down proteins and that is going to lead to the apoptosis of the infected host cell. And so the infected host cell here is going to undergo a pop ketosis. Getting rid of this infected host cell because it lacked those MHC molecules. Now the second irregular pattern that uh these uh natural killer cells can recognize on infected host cells is that these natural killer cells can respond to the FC region or the constant region of I. G. G antibodies that are bound to the surface of an infected host cell and that will lead to the process antibody dependent cellular cida toxicity or A. D. C. C. Which we got to talk a little bit about in some of our previous lesson videos. And so if we take a look at our image down below, notice that the natural killer cells can induce apoptosis via A. D. C. C. Antibody dependent cellular sido toxicity. And so over here on the far left hand side notice that we have a host cell that is infected and this host cell that is infected is going to have a specific proteins on its surface. And I G. G antibodies can recognize and bind to those antigens on the target cell surface. And so these antibodies are somewhat marking this infected host cell. And so the natural killer cell, the NK cell can come along and recognize the FC region of these antibodies. And the FC region is the constant region, basically the bottom of the y shape of the antibody. And so the natural killer cell binds the FC region of the I. G. Antibodies that are bound to the target cell. And when it does that it's going to initiate the release of death packages that includes the perforation and those proteins containing Granules to ultimately uh induce apoptosis in the target host cell. And so ultimately what we're saying here is that these natural killer cells, they lack specificity and so they are part of innate immunity. However, they can work alongside adaptive immunity because again, it's recognizing the FC region of the antibodies uh and they also can kill target cells that lack MHC molecules. And so this year concludes our brief introduction to these natural killer cells and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video
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Problem
ProblemWhat is the main difference between natural killer cells & T cytotoxic cells?
A
Natural killer cells do not need to be activated to target & kill infected host cells, but T cytotoxic cells do.
B
T cytotoxic cells do not need to be activated to target & kill infected host cells, but natural killer cells do.
C
T cytotoxic cells bind to antibodies on the surface of host cells & natural killer cells do not.
D
Natural killer cells are a part of the adaptive immune response & T cytotoxic cells are innate lymphocytes.
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Problem
ProblemCertain viruses have evolved to be able to avoid detection by cytotoxic T cells. These viruses remove the MHC class 1 molecules from the surface of the cell that they are infecting. This ensures that the cytotoxic T cells do not bind to the infected cell and kill the cell and the virus within. Which immune cell is specifically designed to recognize these types of viral threats?
A
CD4 effector cells.
B
T helper cells.
C
Regulatory T cells.
D
Natural killer cells.
E
CD8 effector cells.
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Problem
ProblemHow are natural killer cells able to kill infected host cells?
A
NK cells bind to IgG antibodies on the infected cell's surface and send apoptosis signals to the infected cell.
B
NK cells send perforin and protease granules to the infected cell triggering apoptosis of the infected cell.
C
NK cells bind to antigens on the infected cell's surface and send signals triggering apoptosis of the infected cell.
D
NK cells mark infected cells for destruction and the infected cell will later be destroyed by cytotoxic t cells.
E
A and B.
F
C and D.
G
D only.
H
All of the above.