The immune system is a complex biological network responsible for defending the body against foreign invaders, including pathogens, damaged cells, and abnormal tissues. It operates through two main branches: the innate immune system, which provides immediate, non-specific defense using physical barriers and specialized cells; and the adaptive immune system, which mounts a targeted, memory-based response. This targeted defense involves recognizing unique molecular patterns on foreign substances and generating highly specific protective proteins. Components include various types of blood cells and specialized tissues that work together to detect and neutralize threats, ensuring that subsequent exposures to the same material elicit a faster and stronger defensive reaction.