Question

Natural killer cells target:

infected cells that have lost MHC I surface proteins
	B.	bacterial cells that are coated with complement
	C.	infected cells bound with antibody
	D.	cancerous cells
	E.	Two of the above are correct

Answer 1

E. TWO OF THE ABOVE ARE CORRECT

Natural killer cells are innate lymphoid cells that are considered the first line of defense against the cancer cells. These are cytotoxic to virus-infected and tumor cells that are unable to express class I MHC proteins.

Both natural killer cells and cytotoxic T lymphocytes perform complementary function as both of them target virus-infected cells. however Cytotoxic cells recognized peptides derived from virus and tumor antigens that are presented by MHC I. However, the expression of MHC class I is generally down-regulated by tumors and virus-infected cells and thus cannot be killed by Cytotoxic T cells. Nk cells are unique as they can recognize and kill stressed cells that have down-regulated MHC class I molecules and also can act in the absence of antibodies. They thus do not require activation and show a much faster immune reaction.

Thus, Natural killer cells target:

Infected cells that have lost MHC I surface proteins and cancerous cells (option A and D)

Phagocytes are the cells that allow recognition and ingestion of complement-coated pathogens.