Which statement about NK cells is true?

Which statement about NK cells is true?

• A. They rely upon memory for antigen recognition.
• B. They have the same CD groups as B cells.
• C. They are found mainly in lymph nodes.
• D. They kill target cells without prior exposure to them.

Answer: (D)

Natural killer cells are part of the innate immune response and can kill target cells without prior exposure to them. They detect stressed or abnormal cells through germline-encoded receptors that sense downregulated MHC I or other stress signals, triggering the release of perforin and granzymes to induce apoptosis. This rapid, antigen-independent action is why the statement about NK cells killing target cells without prior exposure is true. They do not rely on memory for recognizing antigens, and their surface markers differ from B cells (they are not the CD19/CD20 type), and they are not confined to lymph nodes but circulate in blood and reside in organs like the spleen and liver. They can also mediate antibody-dependent cellular cytotoxicity via CD16 when antibodies coat target cells, but that does not require prior exposure to the antigen itself.

Natural killer cells are part of the innate immune response and can kill target cells without prior exposure to them. They detect stressed or abnormal cells through germline-encoded receptors that sense downregulated MHC I or other stress signals, triggering the release of perforin and granzymes to induce apoptosis. This rapid, antigen-independent action is why the statement about NK cells killing target cells without prior exposure is true. They do not rely on memory for recognizing antigens, and their surface markers differ from B cells (they are not the CD19/CD20 type), and they are not confined to lymph nodes but circulate in blood and reside in organs like the spleen and liver. They can also mediate antibody-dependent cellular cytotoxicity via CD16 when antibodies coat target cells, but that does not require prior exposure to the antigen itself.