Many different viruses encode proteins that function to down-regulate MHC class I expression on host cells following infection with the virus. This immune evasion mechanism allows the virus to hide from CD8 T lymphocytes that normally detect virus-infected cells by using their T cell antigen receptor to recognize viral peptides bound to MHC class I proteins on the surface of the infected cell. To counteract this immune evasion strategy, NK cells have:
A) Activating receptors that recognize MHC class I proteins
B) A mechanism to secrete antiviral peptides
C) Inhibitory receptors that recognize viral capsid proteins
D) Activating receptors that recognize viral capsid proteins
E) Inhibitory receptors that recognize MHC class I proteins

Question

Quizplus · Accepted Answer

NK cells have inhibitory receptors that recognize self-MHC class I proteins on healthy host cells. This recognition sends an inhibitory signal to the NK cell and prevents it from killing the healthy cell. However, in the case of virus-infected cells, the down-regulation of MHC class I expression results in reduced inhibitory signals to the NK cell, leading to activation and killing of the infected cell. Therefore, inhibitory receptors that recognize MHC class I proteins are crucial for NK cell recognition and elimination of virus-infected cells.

Many Different Viruses Encode Proteins That Function to Down-Regulate MHC