The natural proteins (glycoproteins) produced by the cells of immune system in response to viral infection which protect non-infected cells from further infection are called interferons.
Interferons inhibit the viral replication within host cells, activate natural killer cells and macrophages, increase antigen presentation to lymphocytes and induce resistance of host cells to viral infection. When the antigen is presented to specific T-cells and B-cells, these cells multiply and remove the foreign substance.