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:

Correct Answer: A

Rationale: NK cells use inhibitory MHC I receptors ; low MHC I activates them, not activating MHC or capsid (C/D) receptors.

Correct Answer: B

Rationale: Interferon is produced by virus-infected cells and signals nearby cells to enhance antiviral defenses, unlike lysozyme (antibacterial), histamine (inflammation), or interleukin-2 (immune activation).

Correct Answer: B

Rationale: The secondary response, driven by memory cells, is faster and stronger than the primary, both being specific and involving B/T cells.

Correct Answer: B

Rationale: Innate immunity is rapid and nonspecific, involving receptors and phagocytosis, but does not produce specific antibodies or memory, which are adaptive immunity features.

Correct Answer: A

Rationale: MHC1 presents to CD8+ T cells, activating them against intracellular pathogens, not directly enhancing macrophages.