Final answer:
IFN-a, or Interferon-alpha, is the cytokine known for its significant anti-viral properties, inhibiting viral replication and activating immune cells.
Step-by-step explanation:
The cytokine known for its anti-viral properties is IFN-a (Interferon-alpha). Interferons are a class of cytokines that have early-acting immune responses, particularly against viral infections. When a cell is infected with a virus, it releases interferons, which serve as a warning to nearby uninfected cells. These interferons then stimulate various immune responses such as the destruction of RNA and the reduction of protein synthesis, apoptotic responses in neighboring infected cells, and the activation of immune cells like macrophages, all aiming to inhibit viral replication and spread. Interferons play a pivotal role not just in viral inhibition but also in tumor surveillance.