The human immune system protects the body from pathogens and other foreign substances. It has both innate and adaptive responses. The innate immune system provides immediate defenses through physical barriers, phagocytes, and cytokines. If pathogens breach these defenses, the adaptive immune system mounts a specific response by activating lymphocytes and developing immunological memory. The adaptive response allows for faster and stronger protection upon subsequent exposures. Overall, the immune system has evolved complex communication networks and response strategies to recognize self from non-self and protect the host while avoiding autoimmunity.