The immune system is a complex network of cells, tissues, and organs that protects the body against disease. It recognizes and destroys harmful substances, such as bacteria and viruses. Also, it produces antibodies that destroy these foreign substances.
Immunity is also known as adaptive immunity because it adapts to each new threat it encounters. The immune system has memory, so once it has fought off an invader it remembers how to fight that specific invader again in the future.
The immune system consists of two parts: innate immunity and adaptive immunity. Innate immunity is a normal part of our bodies that protects us from infection without having to learn anything new about a particular threat. Adaptive immunity is acquired through exposure to an antigen (foreign substance) which causes an immune response that produces memory T-cells and antibodies specific for that antigen.
The immune system has three main functions:
It has evolved to recognize specific molecules on the surface of cells as “self” or “non-self.” When it recognizes a non-self molecule, it triggers an immune response that eliminates invading organisms and damaged or abnormal cells.
The immune system produces antibodies that bind to bacteria or viruses in order to neutralize them so they can’t infect cells in your body. Antibodies also help alert other parts of the immune system to infected cells by binding to non-self molecules called antigens on their surfaces.
The immune system also produces lymphocytes called T-cells that directly attack cancer cells by recognizing antigens displayed on their surfaces.