Final answer:
Interferons are small proteins secreted by virus-infected cells to warn neighbor cells and stimulate antiviral defenses, playing a critical role in the immune response against viral infections.
Step-by-step explanation:
The small proteins secreted by virus-infected cells to help defend cells that have not yet been infected are known as interferons. Interferons are a type of cytokine, which are critical in the immune response to viruses. These proteins are released by cells when they are infected by a virus and they serve as a signal to neighboring cells. When surrounding cells receive this signal, they are prompted to produce compounds that can prevent viral replication. Thus, interferons play a crucial role in controlling viral infections by preventing the spread of the virus to uninfected cells and by activating macrophages and other cells that can attack the virus.