NK cells can be activated following recognition of a virus-infected cell, if that cell has down-regulated expression of MHC class I proteins on its surface. However, NK cells can also recognize infected cells or tumor cells, even if they still express MHC class I proteins. In this latter case, activating receptors on NK cells are recognizing:
A) Molecules on the target cell up-regulated by cellular or metabolic stress
B) Cytokines secreted by the virus-infected or tumor cell
C) MHC class I-like decoy molecules encoded by the virus
D) Mutated self-proteins expressed by the tumor cell
E) Double-stranded DNA in the cytoplasm of the infected or tumor cell

Question

Quizplus · Accepted Answer

Activating receptors on NK cells can recognize molecules on the target cell that are up-regulated by cellular or metabolic stress, such as induced self-proteins or viral proteins that are not normally expressed in non-infected cells. This allows NK cells to recognize infected or tumor cells that may still express MHC class I proteins.

NK Cells Can Be Activated Following Recognition of a Virus-Infected