In addition to your body's own ‘average Joe working cells’, you are internally patrolled by a microscopic police force; the cells and molecules of your immune system. These cellular cops are constantly on the lookout for bad guys, finding interlopers and eliminating them. Bad guy microbes (pathogenic bacteria, fungi, eukaryotes & viruses) are everywhere. You can't avoid them, and your body's police force is constantly intervening to prevent you from being colonized by pathogens.
Nonspecific Immune Defenses
Nonspecific defenses are general ways in which your body fights infection; tactics that do not target or recognize specific microbes, but deter the ‘bad guys’ none the less. The human body has two nonspecific lines of defense against pathogens.
The First Line of Defense
The first line of immune defense has both physical and chemical components, and consists of your skin and its products. Your skin, mucous membranes, sweat and oil (sebum) are all part of an external fortress that helps prevent pathogens from getting inside you in the first place.
The Second Line of Defense
The second line of nonspecific immune defense comes into play when pathogens succeed in penetrating the skin or mucous membranes. The players in nonspecific defense consist of cells, antimicrobial chemicals, and processes; not physical barriers. Many components of second line defense are contained or originate in the blood, including leukocytes (white blood cells).
Specific or Acquired Immunity - The Third Line of Defense
Your body’s third line of immune defense is a ‘smart system’ that can learn and change. Specific immunity involves cells and cell products that can recognize and remember specific pathogens. This is why you become ill with some infectious diseases one time one only, and never again. This is because, after initial exposure, your body has a police squadron of cells specifically trained to find and destroy that particular pathogen. Our specific immunity is also why we can use vaccinations to prevent illness.
A vaccination usually contains an either dead or weakened microbe that can no longer cause disease. Intentionally exposing the body to this weakened microbe, is kind of like showing the cells of our specific immune system a ‘wanted poster’ so that if they run into this bad microbe in the future, they can identify and eliminate it.
More Immunology Information
To learn more about the human immune system, see Science Prof Online's PowerPoint lecture and articles on Human Immunology or go to John Rosses page on The Human Immune System. Photo of white blood cell by Dr. Triche of the National Cancer Institute.
