suaysuay at atenista.net wrote:
>I'm confused about this one very basic aspect of immunity:
>>NK cells generally kill cells that display non-self MHC I-peptide complexes, CD8 cells kill only cells bearing a specific non-self antigen. Given that viruses mutate, and NK cells seem to have a 'better safe than sorry' attitude, wouldn't NK cells be "better" than CD8 cells in clearing up an infection? Why is it that in some viral infections, NK cells are only good for controlling the infections but CD8 cells are needed to finish the job?
>>http://biowww.net/mynews/tree.php?group_name=bionet_immunology&begin=0>>You've got the NK cell thing wrong. NK cells have receptors (termed
Killer Inhibitory Receptors/KIR's). These KIR's bind to class I MHC in
an antigen independent manner. Or in other words the receptor detects
if there is MHC I on the surface of the cell. NK cells kill any cell
that lacks or has unusually low MHC I on their surface. This is done as
many viruses down regulate MHC molecules, as do some cancers. CD8+
T-cells only bind a specific antigen-MHC complex, and this binding
usually results in the death of the target cell. It is this antigen
specificity that makes T-cells central to clearing viral infection - NK
cells can only detect cells in the later phases of viral infection,
whereas T-cells can detect any virally infected cell.
Hope this helps
Bryan Heit
