Final answer:
Type I interferons activate macrophages, which are integral in the early immune response to fight off viral infections. These interferons also prime neighboring cells against infection, stimulate apoptosis of infected cells, and are regulated by helper cells like Th1, enhancing their immune activity.
Step-by-step explanation:
The main innate immune cell that is activated by Type I interferons in response to viral infections are macrophages. Interferons are types of cytokines, and they play an essential role in the body's defense mechanisms. When a cell is infected with a virus, it releases interferons to warn neighboring cells. These interferons trigger a response in other cells that helps combat the infection by inhibiting viral replication. Not only do the interferons prepare neighboring cells to defend themselves by destroying RNA and reducing protein synthesis, but they also signal infected cells to undergo apoptosis, and importantly, they activate immune cells such as macrophages. Macrophages are able to engulf and digest pathogens and often become activated by the presence of interferons to bolster the body's early, antiviral immune response when first exposed to a pathogen. Additionally, Th1 cells, a type of helper T cell, can secrete cytokines that further regulate the activity and development of immune cells like the macrophages.