The Immune System Definition
A body system that protects against infection, the immune system is composed of cells, organs, and proteins that work together to protect the body from viruses, bacteria, and other invaders. Without the immune system, people constantly would be sick. Overall, the immune system is comprised of various parts that serve various functions, from recognizing and acting against the invaders, or antigens, to working throughout the body to prevent infection, and finally to remembering antigens from previous attacks in order to put up an even stronger fight in future instances.
The Immune Response
The immune response is the way in which your body recognizes and defends itself against bacteria, viruses, and other substances that are foreign and harmful. It is the job of the immune system to protect our bodies from harmful invaders by recognizing and responding to antigens. Typically proteins, antigens reside of the surface of cells, viruses, fungi, or bacteria, but antigens also may be nonliving substances including toxins, chemicals, drugs, and foreign particles like splinters. The immune system remembers, recognizes, and destroys antigen-containing substances.
The Immune System’s First Line of Defense
The immune system constantly works to ward off invading microbes that intend to cause disease and has multiple lines of defense. The first line of defense for our bodies includes our skin and mucous membranes that act as a barrier against microbes seeking to penetrate them and enter the body. For example, our blood clots and seals our words to prevent microbes from entering. In fact, our skin, digestive system, and the lining of our nose are covered by microbes, or normal body flora, that help protect us from becoming infected with harmful microorganisms by serving as the physical barrier.
Other items in our first line of defense are our mucus, enzymes in our tears, saliva, stomach acid, and urine. When our immune system senses that invaders are trying to enter, it triggers the production of more tears or more mucus, creating an immune response, in order to prevent further microbes from entering the body and to flush out those that already entered.
The Immune System’s Second Line of Defense
When microbes enter the body, the immune response activates the body’s second line of defense: phagocytes. Phagocytes, a type of white blood cell, move around and send out pseudopodia, allowing them to surround invading microbes and engulf them. Phagocytes also release digestive enzymes that break down trapped microbes, preventing them from doing harm. This part of the immune response is called phagocytosis.
The Immune System’s Third Line of Defense
Full-blown immune response is the body’s third, and final, line of defense. When antigens invade, the immune system sees them as threats and stimulates the immune response. The immune system produces antibodies against the antigen. Antibodies engage in a battle to fight off the invading antigens. Specialized white blood cells, called lymphocytes, recognize antigens as being foreign and produce the antibodies that are specific to the antigen. The antibodies have unique binding shapes that lock onto the corresponding antigens’ shapes, so that the antibodies are able to destroy the antigen, which then becomes engulfed and digested by macrophanges.
Another function of the immune response involves white blood cells producing antitoxins, which are chemicals that destroy the toxins produced by some bacteria when they invade the body. Tetanus, diphtheria, and scarlet fever are diseases associated with bacteria that secrete toxins and illicit this type of immune response.
The immune response diminishes as the invading microbes are destroyed. And, people typically don’t get a disease more than once because the immune system creates memory cells that are specific to each disease’s antigen. These memory cells first recall the microbes that cause the disease and then produce the necessary antibody when the body is exposed to the same type of infection again. The immune response helps to destroy the pathogen, in order to prevent the symptoms of the disease from occurring a subsequent time. Image via Flickr by NIAID
The immune system is an amazing body system that is at work all of the time to keep us as healthy as possible. The processes involved in the immune response have several components and layers, as the body works to defend against invaders to prevent infection and disease.