The substance produced by a cell in viral infection that can protect other cells from further infection is

1. serotonin     
2. colostrum   
3. interferon       
4. histamine

(c) The cytokine-barriers include interferons. These are the proteins secreted by virus

infected cells, which protect non-infected cells from further viral infection.

Serotonin It is a neurotransmitter that leads to depression.

Colostrum It is present in the lactating mother's breast milk, contains antibodies which
protect the newborn against disease.

Histamine Histamine is also a neurotransmitter involved in inflammatory response.