The answer is interferon.
Interferon is not cell, but is a group of glycoproteins known for their role in inhibiting viral infections by preventing virus multiplication in cells.
Interferon also helps in the fight against infection by stimulating the entire immune system to fight the infection.
There are different types of interferon. They include interferon-alpha which is made by leucocytes and interferon-gamma which is made by fibroblasts after viral infection.
The first interferon was discovered by Alick Isaacs and Jean Lindenmann in 1957.