The immune response refers to the way the body fights back against bacteria, viruses and other substances that are harmful to the body. The immune system responds to antigens, which are large molecules on the surface of cells, viruses and fungi. Non-living substances, such as a splinter, can also be antigens. Any substance entering the body that contains one of these antigens is identified and destroyed by the immune system.

The body’s inflammatory response is produced when tissues are injured by bacteria, trauma, toxins, heat and other substances. The damaged tissue will release chemicals that cause blood vessels to leak into the tissue, resulting in swelling. Such swelling isolates the foreign substance, preventing contact with other body tissues. The chemicals that are released from the tissue also attract white blood cells that surround, engulf and destroy the foreign substance in a process known as phagocytosis.

Another aspect of the immune response is acquired immunity. As the body is exposed to an antigen, it builds a response that is specific to that antigen. This is achieved with the aid of a special class of white blood cells, known as lymphocytes. Lymphocytes recognize what is part of your body and what is foreign. For instance, if skin from one part of your body is grafted on another part, it will likely adhere and survive. But if the skin is from someone else, lymphocytes migrate to the area, recognize “That’s not mine” and begin rejecting it. They also have a “memory” that aids you to be immune to various diseases.