Which type of innate immunity is exhibited by interferons secreted by virus-infected cells to protect non-infected cells?

The correct option is Cytokine barriers.

Innate immunity is the defense system with which we are born. It protects us against all antigens and consists of four main types of barriers: physical, physiological, cellular, and cytokine barriers.

Cytokine barriers specifically involve chemical messengers released by cells to coordinate immune responses. When a host cell is infected by a virus, it secretes special proteins called interferons.
Interferons belong to the class of cytokines and act as signaling molecules. They diffuse to neighboring, non-infected cells and stimulate them to synthesize antiviral proteins, thereby protecting these healthy cells from subsequent viral infection and replication.

Let's briefly distinguish this from the other options:
1. Physical barriers: These block the entry of microorganisms into the body (for example, the skin and mucus coatings of the respiratory, gastrointestinal, and urogenital tracts).
2. Physiological barriers: These prevent microbial growth through physiological conditions (such as acid in the stomach, saliva in the mouth, and tears from the eyes).
3. Cellular barriers: These involve specialized white blood cells that phagocytose and destroy microbes (like polymorpho-nuclear leukocytes, monocytes, and natural killer cells).

Therefore, because interferons are secreted proteins that signal and protect non-infected cells, they are classified under Cytokine barriers.