Final answer:
Interferon in the blood acts as a nonspecific chemical barrier, which is part of the innate immune system's defense against pathogens.
Step-by-step explanation:
The innate immune system includes several mechanisms to fend off pathogens, one of which is the release of interferons. Interferons act as a nonspecific chemical barrier that is part of the body's innate immune defense. Rather than serving as a physical barrier like the skin, or a cellular response such as phagocytosis by white blood cells, interferons are proteins that interfere with viral replication and activate immune cells. As chemical messengers, they signal to neighboring cells to increase their defenses against viral infections and also alert immune cells to the presence of pathogens.