Reason why Natural Killer Cell don't kill RBC
NK = Natural Killer HLA = Human Leukocyte Antigen = MHC = Major Histocompatibility Complex
Killer T Cells kill cells whose MHC windows show foreign antigen. But if a pathogen destroys those MHC windows, then Killer T cells can't detect those infected cells.
Simply speaking Natural Killer Cells check for cells without MHC and kill them.
NK cells have activating and inhibitory receptors. And the balance of signals from those receptors tells whether to activate and kill the cell or not.
MHC molecules bind to inhibitory receptors and if they are lacking the activating signals wins and NK is activated.
RBC lack MHC, because MHC are only present in nucleated cells. But RBC are safe from NK because, RBC also don't have the molecules that bind to activating receptors.
Q: As you know, RBCs do not have any HLA molecules, so how do these cells protect themselves from the NK killing activities?
Ans: RBC's do not have MHC class I molecules to engage inhibitory receptors of NK cells and also do not express receptors that engage NK activating receptors. In erythroblastosus fetalis , RBC lysis is via ADCC in which antibodies binding to RBC antigens bind to Fc receptors on NK cells mediating lysis. Hope this is explains the reason.
