How are antibodies and interferons different?

Markers and fighters. The presence of antibodies indicate exposure to an infection. Antibodies are markers. They can be tested in the blood. Interferons are substances that suppress viruses. These are fighters. They cannot be tested for.
Immune System. Interferons are proteins made and released by host cells in response to the presence of pathogens such as viruses, bacteria, parasites or tumor cells. They are messengers. Antibodies are the foot soldiers of the immune system involved in actual protection.