Final answer:
NK cells, which are part of the innate immune system, recognize and kill virally infected dendritic cells that lack normal MHC I molecule expression by inducing apoptosis. This leads to the subsequent phagocytosis of the cellular debris.
Step-by-step explanation:
When NK cells outnumber virally infected dendritic cells, the NK cells detect the lack of proper MHC I molecules on the surface of these infected cells. Normally, healthy cells will present MHC I molecules, which are responsible for displaying cellular contents to immune cells, including NK cells. A reduction in MHC I expression is a common strategy by viruses to evade detection by cytotoxic T cells. However, this makes the infected cells more susceptible to NK cells, which look for the absence of MHC I molecules as a sign of an unhealthy cell, such as a virally infected or cancerous cell.
Once an NK cell recognizes a cell as unhealthy due to altered MHC I expression, it will initiate the process of apoptosis, effectively instructing the infected cell to self-destruct. This is followed by phagocytic cells which engulf and digest the remnants of the destroyed cells. Consequently, the presence of an adequate number of NK cells can lead to the efficient elimination of virally infected dendritic cells before the virus has the opportunity to replicate further or the infected cells can cause additional harm.