Interferons are proteins produced by cells in response to infections, playing a key role in the immune system. They help regulate immune responses, activate antiviral defenses, and influence immune cell activity. There are three types: Type I (e.g., IFN-α, IFN-β) for antiviral defense, Type II (e.g., IFN-γ) for immune regulation, and Type III (e.g., IFN-λ) for mucosal immunity. Interferons are used in treating viral infections, cancers, and autoimmune diseases, though they can have side effects like flu-like symptoms.