NK cell-mediated killing?

xsimmx simm at yahoo_nospam.com
Thu Dec 28 11:30:41 EST 2000

activation of NK doesn't deal with what's on the MHC but the integrity
of MHC as you said. Viral and malignant changes in a cell will result
in some of the "self" proteins (such as MHC) to be altered. Also some
cell markers will dissappear. This, I believe, is what the NK
lymphocyte looks for. 

I like to think of it in terms of two hand shake. If one hand is free
it can be used to hit the other person on the head :) if both hands
are busy shaking, you move on to the next guy. 

hope this helps, 

Maciej Simm

On 27 Dec 2000 19:19:02 -0000, kdelgert at vt.edu ("Klaus D. Elgert")

>In the midst of the holiday cheer, would some NK cell gurus help 
>clarify stuff to a macrophage person?  The following questions arose 
>during a debate/discussion we had in a graduate immunology course.
>Literature suggests that the NK cell's ability to recognize and kill 
>a virally infected target cell depends on the integrity and amount of 
>target cell surface class I MHC proteins.  This integrity and amount 
>of surface class I MHC proteins determine whether the NK cell's 
>inhibitory or activating receptor signals prevail.  Given that 
>scenario, what is the mechanism by which NK cells distinguish class I 
>MHC carrying self-peptides from class I MHC carrying viral derived 
>peptides?  In particular, if the virally infected target cell's 
>amount and class I MHC molecule integrity are normal (as cells 
>targeted by cytotoxic T lymphocytes [CTLs]), do/can NK cells kill 
>this target cell?  In more technical terms, if NK cells recognize 
>class I MHC molecules displaying self-peptides as a "no kill" ligand 
>would the replacement of self-peptide with viral peptide in class I 
>MHC molecules be enough to cause a failure to nullify the "kill" 
>signal?  Or do NK cells only kill virally infected cells that have 
>altered class I MHC molecules or reduced (or inhibited) expression of 
>class I MHC molecules?  If the answer to the last question were yes, 
>then it would be wrong to say, at least in a generic way, that all 
>cells infected by virus activate NK cells?  The flipside would be 
>that all virus-infected cells must have either altered (does every 
>molecule have to be changed?) and/or reduced or inhibited expression 
>of class I MHC molecules for NK cells to recognize and kill the 
>virus-infected cells.  So if MHC things are "normal" on a 
>virus-infected cell, only CTLs work.  If MHC things are "abnormal" on 
>a virus-infected cell, only NK cells work.

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