A soluble mediator produced by lymphocytes is known as a

• A. Produced by granulocytes and affects lymphocytes
• B. Produced by lymphocytes
• C. Produced by plasma cells
• D. Secreted by bacteria

Answer: (B)

Soluble mediators in the immune system are signaling proteins called cytokines. When these mediators come from lymphocytes, they’re often referred to as lymphokines. The key idea is the origin of the mediator: if the description specifies that it is produced by lymphocytes, the correct understanding is that the mediator is lymphocyte-derived. This sets it apart from mediators produced by granulocytes, antibodies produced by plasma cells, or substances secreted by bacteria. In other words, the concept being tested is recognizing that a soluble mediator described as coming from lymphocytes is inherently produced by lymphocytes. Examples of lymphocyte-produced cytokines include IL-2 and interferon-γ, which regulate various aspects of the immune response.