Final answer:
NK cells detect virally infected cells by their lack of MHC I molecules and induce apoptosis through fas ligand, complementing cytotoxic T cells in controlling viral infections.
Step-by-step explanation:
HNatural killer (NK) cells play a crucial role in the immune response against virally infected cells, which cytotoxic T cells also target. When a cell becomes infected with a virus, it may stop presenting MHC I molecules on its surface as a way to evade the immune system. However, this makes the infected cell more susceptible to NK cell recognition. NK cells can detect the absence of MHC I and respond by inducing apoptosis in the infected cell.
NK cells achieve this by expressing fas ligand, which binds to the fas molecule on the surface of the infected cell. This interaction triggers apoptotic signals, leading to the death of the infected cell and preventing the spread of the virus. It's important to note that this response is a key element of the innate immune system and acts as the first line of defense against intracellular pathogens like viruses, providing rapid protection until the adaptive immune system can mount a more specific response.
In conjunction with cytotoxic T cells, NK cells contribute to the body's defense by limiting viral replication and helping to clear the infection. Together, they form a powerful duo that ensures virally infected cells are effectively recognized and destroyed before they can cause further harm.