Answer:
D. Interferons
Explanation:
Interferons are the chemical signals (secretary proteins) responsible for activating non-infected cells so that they could fight a virus. In case of a viral infection, a cell infected by virus release interferons to let neighboring cells know the presence of a virus so that they could enhance their anti viral defense.
Interferons are of 3 types:
1) Interferon α
2) Interferon β
3) Interferon γ
Interferon α & β are secreted by white blood cells while interferon γ is mainly synthesized by natural killer cells.
