Which statement about NK cell activation is true?

Which statement about NK cell activation is true?

• A. The activation is determined by a balance of inhibitory and activating signals.
• B. It relies on antigen-specific receptors.
• C. It requires antibody coating to function.
• D. It only responds to pathogens that have been fever-induced.

Answer: (A)

Activation of natural killer cells hinges on a balance of signals received through their activating and inhibitory receptors. Inhibitory receptors recognize normal self MHC class I molecules and send a quieting signal that prevents killing. When a cell is stressed, infected, or transformed, it often downregulates MHC I and upregulates stress ligands, tipping the balance toward activation as activating receptors engage those ligands. The net outcome determines whether the NK cell will release cytotoxic granules and kill the target. This innate response does not rely on antigen-specific receptors like TCRs or BCRs. Antibody coating can engage NK cells through Fc receptors to mediate a specific pathway called antibody-dependent cellular cytotoxicity, but it isn’t the general requirement for NK cell activation. Fever states aren’t the defining trigger; the critical factor is the integrated signal balance.

Activation of natural killer cells hinges on a balance of signals received through their activating and inhibitory receptors. Inhibitory receptors recognize normal self MHC class I molecules and send a quieting signal that prevents killing. When a cell is stressed, infected, or transformed, it often downregulates MHC I and upregulates stress ligands, tipping the balance toward activation as activating receptors engage those ligands. The net outcome determines whether the NK cell will release cytotoxic granules and kill the target. This innate response does not rely on antigen-specific receptors like TCRs or BCRs. Antibody coating can engage NK cells through Fc receptors to mediate a specific pathway called antibody-dependent cellular cytotoxicity, but it isn’t the general requirement for NK cell activation. Fever states aren’t the defining trigger; the critical factor is the integrated signal balance.