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")
wrote:
>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.
>>Thanks,
>Klaus
>>>---
