Which protein is produced by a virus-infected cell to help fight infections?

Interferon is a type of protein that is specifically produced by virus-infected cells as part of the body's immune response to fight infections. When a cell becomes infected by a virus, it releases interferons, which serve as signaling molecules to alert neighboring cells about the presence of the virus. This alert prompts the neighboring cells to heighten their antiviral defenses, making them more resistant to infection. Additionally, interferons enhance the activity of immune cells such as natural killer cells and macrophages, which play crucial roles in defending the body against viral infections.

The other proteins listed, such as interleukins and cytokines, are important components of the immune system, but they do not specifically describe the response of virus-infected cells to viral infections in the same way that interferons do. Antibodies, on the other hand, are produced by B cells in response to an infection but are not directly produced by virus-infected cells; instead, they specifically target and bind to antigens on pathogens to neutralize them. Therefore, interferon is the most accurate answer in the context of proteins produced specifically by virus-infected cells to combat infections.