The immune system is the body’s defense system against invading pathogens such as bacteria, viruses, and toxins. It functions by detecting and destroying these foreign substances. It is composed of various cells and organs that work together to protect the body and recognize disease-causing agents, also known as antigens. This includes lymphocytes, macrophages, and natural killer cells. Lymphocytes are white blood cells that identify and destroy antigens, while macrophages are specialized cells that engulf and digest pathogens. Natural killer cells recognize cells that have been taken over by a virus and immediately initiate an attack to destroy the diseased cell and its viral load. When a pathogen is detected, the immune system produces antibodies to bind to and neutralize the antigen. It also triggers inflammation in the area to attract other immune cells to help fight the infection. The immune system also remembers previous encounters with antigens, so it can quickly produce the correct antibody when it detects the same pathogen again.