The immune system is a large network of organs, white blood cells and proteins that protects the body from germs and other substances that may make you sick. It also helps the body heal from infections and injuries.

The first line of defense against germs is the skin and mucus membranes that line the body’s natural openings, such as the mouth, nose and anus. They act as a physical barrier and release chemicals that create a hostile environment for invaders or directly attack and destroy them. This is called innate immunity.

When the immune system does recognize a foreign substance, such as a protein on the surface of a disease-causing bacteria, it triggers a series of events that eventually kill the pathogen. These include vasodilation (widening of the blood vessels), increased permeability of the skin and other tissues, and recruitment of immune cells to the infection site by chemokines. These cells include helper T cells, which plan attacks on infected tissue, and killer T cells that destroy the invading pathogens.

In addition, antibodies are produced by B cells that recognize specific antigens. These antibodies can bind to the pathogen and neutralize it or mark it for destruction by other immune system cells and molecules. When B cells that have created antibodies “remember” an antigen, such as a toxin or piece of a virus, they increase production of these antibodies and can respond more quickly if the antigen comes back.

The immune system depends on a healthy, balanced diet for its raw materials. Some evidence suggests that certain dietary factors, such as a high intake of simple sugars and processed foods, can negatively affect immune function. However, more research is needed to understand how dietary factors affect the ability of the immune system to perform its jobs.