Mechanisms

Mainly derived from the bone marrow, NK cells routinely survey immune cells by checking them for the expression of certain markers. Normal, healthy cells display markers that naturally inhibit NK cell activation. However, upon stress, cells may downregulate markers like MHC I. If an NK cell sees a cell is “missing self” or has an overabundance of NK activating ligands, the NK cell will target that cell for destruction, primarily killing through granzyme and perforin release and FasL-mediated cytotoxicity. In this manner, NK cells help to monitor for viral infection and tumor cells.

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