On thing that the other answerer's didn't mention are the KIR receptor
pairs (homologue of ly49?). killer cell inhibitory receptor. this also
acts as a toggle switch of sorts.
"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
>> ---
