IL6 and depressive symptom measurement: IL-6 is a key mediator of inflammation; it is produced in response to cellular injuries and infections.56 IL-6 plays a major regulatory role in coordinating immune response and the host defense mechanism.57 In addition to its role as an immune mediator, IL-6 may also modulate neurotransmission, and there is evidence that it plays a role in the pathomechanism of depression.58