Which hormone-like chemicals facilitate communication between the brain and the immune system?

• A. Hormones
• B. Cytokines
• C. Neurotransmitters
• D. Chemokines

Answer: (B)

Signaling molecules that mediate communication between the immune system and the brain are cytokines. These proteins are released by immune cells (like macrophages and T cells) and can travel through the circulation or signal via neural pathways to influence brain activity. Cytokines act in hormone-like fashion: they bind to receptors on neurons and glial cells, altering neural circuits and affecting processes such as fever, sleep, appetite, and mood. The brain can also produce cytokines in response to immune challenges, creating a bidirectional dialogue that coordinates the body’s response to infection or inflammation. While chemokines are related signaling molecules, their primary role is directing immune cell movement rather than broadly communicating with the brain. Neurotransmitters are focused on rapid synaptic communication between neurons, not the systemic immune-brain messaging described here.