How are Natural Killer (NK) Cells Different from Cytotoxic T

Question

How are natural killer (NK) cells different from cytotoxic T (TC) cells?
A) NK cells induce apoptosis in their target cells, whereas TC cells are professional phagocytes.
B) NK cells kill virus-infected cells, whereas TC cells kill cancerous cells.
C) NK cells kill cells with a high level of class I MHC protein expression, whereas killing by TC cells requires low expression levels.
D) NK cells respond quickly to a virus infection, whereas the activation of TC cells to become cytotoxic is a slow process.
E) NK cells are normally abundant in the tissue even before infection, whereas TC cells are mostly in the bloodstream.

Accepted Answer

NK cells are components of the innate immune system, which responds quickly to infection; NK cells circulate in a partially active state and therefore can kill virally infected cells when they first encounter them. TC cells need to be activated in a slow process in a lymphoid organ before they can kill virus-infected cells.