Immunology: NK Cells and Red Blood Cells

[Czarcasm]

So if Natural Killer cells mode of action is to destroy all cells that do not express the MHC-I receptor and because all nucleated cells in our body (also, platlets) have this receptor -- why then do red blood cells not get destroyed by NK cells? They lack the MHC-I receptor. Does it have anything to do with their structure, size, or is there something I'm missing here?

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[Cmdr_Shepard]

They do. But there's enough regenerated RBC's that the hematocrit stays stable.

Edit: I should probably add that old or damaged RBC's are engulfed by phagocytes. But NK likely also avoid them because of some inhibitory engulfment signal from proteins on the RBC surface. Even if some are taken up by NK cells, it's likely not many.

 

[Czarcasm]

Great, thank you!