NK Cells- 2% circulating lymphocytes, derived from bone marrow, lack specific TCR for Ag recognition; important component of innate immune system
- NK cells identify transformed (tumor) or virally infected cells through the downregulation of MHC I
- Destroy cells via granzymes (induce apoptosis by initiating DNA fragmentation) and perforins (forms pores in cell membrane); may also destroy via FAS and TRAIL ligands
- Activated by IL-2, IL-12, and IL-15; express CD2 (no CD3), CD56, and CD16
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