Final answer:
The immune system uses cytokines as chemical messengers for communication. Cytokines regulate immune responses and stimulate various defenses.
Step-by-step explanation:
The immune system uses cytokines as chemical messengers for communication. Cytokines are hormone-like molecules that facilitate communication between cells of the immune system. When a pathogen is recognized as foreign, cytokines are released to regulate immune responses and stimulate various defenses.