What are proteins that activate the immune system and fight viruses?

Antibodies and cytokines.

Antibodies are proteins that are produced by the immune system in response to the presence of a foreign substance, such as a virus. Antibodies bind to the virus and neutralize it, preventing it from infecting cells. Cytokines are proteins that are produced by the immune system in response to the presence of a foreign substance. Cytokines help to activate the immune system and fight off infection.