Interferons can be defined as -

The correct answer is Option (2) → Proteins secreted by virus infected cells

Interferons are part of the cytokine barrier of innate immunity. This is the defence with which we are born.

(1) Proteins secreted by bacteria infected cells — Incorrect. Interferons are triggered by viruses. Bacteria are met by other defences, such as phagocytic cells.

(2) Proteins secreted by virus infected cells — Correct. Virus-infected cells secrete proteins called interferons. They protect the neighbouring cells that are not yet infected from further viral infection.

(3) RNA secreted by fungi infected cells — Incorrect. Interferons are proteins and not RNA. They are not tied to fungal infection.

(4) Proteins secreted due to allergy — Incorrect. In an allergy, mast cells release chemicals such as histamine and serotonin. These are not interferons.

NCERT Extract:
Innate Immunity – …