can someone please explain difference between cytoxic t cells and natural killer

[alisepeep]

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do natural killer cells respond to lack of MHC and presence of lectin? (also to tumor cells)
but cytoxic only respond when there is evidence of viral infection?

 

[xeroun]

So NK cells have two types of receptors: One is an activator and the Other is is an Inhibitor.
NK Cells do not express antigen specific receptors. Their targeting is not MHC-restricted... and no memory generated from their activity.
Basically NK cells Go up to a cell and their Activation receptor Binds to Lectins(found in many pathogens). Now if this is a NORMAL cell it should have MHC I expressed also. NK cell inhibitory receptor binds MHC I and sends an inhibitory signal to stop NK cell from releasing Perforins and Granzymes. If the cell is not normal - Virus infected cells down regulate MHC I and Tumor cells tend to also loose MHC I - Then nothing for inhibitory receptor to bind to and Activation signal causes release of Perforins and Granzymes.

CTL cells recognize it targets based on interaction of its TCR and MHC I on target. Normal functioning cells produce a Normal MHC I that no CTL cell in your body should recognize (remember selection process). If the cell is infected with Intracellular organism or is a tumor cell then they express an abnormal MHC I with a non-self peptide that some CTL will have a TCR that can bind to it and kill the Abnormal cell through Perforin and Granzyme combo.


I think of NK cells as a crazy guard that goes around with a loaded gun. When he is sent out on patrol he interrogates everyone he meets by basically pointing loaded gun at their face and asking for identification. Cant present proper identification---> BAM.

CTL cells are really helpers. Basically an infected cell or a Tumor cell (before it goes totally crazy) use their last breath to call CTL cell to kill it before harm can come to host. The CTL comes by and sees MHC I signal and takes pity on poor cell and kills it for the good of all.

 

[JP2740]

Don't NK also respond to MHCs, considering interferons upregulate MHCs but also activate NK to kill?

 

[xeroun]

I dont think NK cells respond to MHCs in classic sense as do say T cells: Cell with MHC + Foreign protein recognized by TCR leading to T cell activation and death of Cell.

NK cells killing ability is inhibited by MHC I.

NK cells are usually found closely associated with Dendritic Cells in lymphoid tissue and inflammation sites. Dendritic cells can activate resting NK cells by secreting IFN, and IL 12, 15, 18. Up regulation of MHCs and NK cell activity simultaneously would be better for proper response. All the normal cells will increase their MHC and would not get killed by mistake. Tumor cells or infected that has lost the ability to make MHC I will not be able to respond to the IFN and will stand out even more.

Some viruses use this to their advantage. Certain strains of HCV actually cause infected cells upregulate normal MHC I. This allows them to escape killing by NK cells.

 

[alisepeep]

thank u! that was a really good explannation!

 

[John Lannister]

They both wreck foreign **** in the body.

 

[drstarter]

Good explanation! thanks

 

[John Lannister]

Good explanation! thanks

No problemo.