General Features of the Immune System

Your immune system is fighting a constant battle with a wide variety of tiny microbes in the environment. Many of these microbes, typically viruses and bacteria, have the potential to create disease. To defend against these potential diseases, your body has developed a wide variety of defense mechanisms to protect itself from harm. Our ability to survive in this hostile environment is a testimony to the effectiveness of these defense mechanisms.

The immune system functions primarily by determining what is “self”, and what is “nonself. Once an organism is identified as nonself, it is targeted for destruction by your immune system. The immune system has a complex structure, with many levels of defense. There are many specialized types of cells, tissues, and proteins which are specially designed to attack foreign invaders.

The immune system is very broadly broken up into two distinct categories. The first category is the innate immune system. The innate immune system is the first line of defense against invading bacteria and viruses. It involves physical and chemical barriers which are not specific to any one particular pathogen, but rather act as a broad defense against a wide variety of disease causing microbes.

Your skin is the first barrier involved in the innate immune system defenses. Skin has the ability to defend your body against viruses, bacteria, and fungi which would otherwise be able to gain access to your body and cause disease. If the skin is broken or cut, your risk of infection increases substantially.

In addition to your skin, your body makes a wide variety of chemicals which are designed to attack invading microbes. The innate immune system has many nonspecific chemicals designed to damage any non-self microbe that may be present in the body. One of these chemicals is known as lysozyme. Lysozyme is an extremely common chemical involved in the innate immune defenses which targets a wide variety of different bacteria. When lysozyme comes into contact with these bacteria, it disrupts their cell walls and kills them. Your body is constantly making lysozyme, and does not need to have exposure to a particular bacteria in order to manufacture it.

Another example of the innate immune system is the acidity of your stomach. Acid in your stomach prevents colonization of many bacteria and viruses when you eat them in food. Should bacteria or viruses penetrate these initial nonspecific defenses, there are other cells within your body which are specifically designed to attack invading microbes. Cells known as natural killer cells, phagocytes, and antigen presenting cells are all involved in various ways with the innate immune system. The exact functioning and structure of these defenses is somewhat complicated and outside the scope of this general article.

Of course, the nonspecific nature of the innate immune system is oftentimes not enough to repel a potential infection. The second and more complicated aspects of your immune system are known as the acquired immune responses. These immune defenses are referred to as acquired because they require activation and training by your immune system in order to function. They are also specifically adapted towards individual invading microbes. This makes them highly effective in killing their target, but there is often a time delay between an infection and the response.

The two primary types of cells involved in the acquired immune response are B-cells and T-cells. These cells are both types of lymphocytes. B-cells and T-cells will work together to become highly specialized and effective at killing specific bacteria and viruses. How they do this is somewhat complicated, and is the subject of entire classes of coursework during medical school.

In the end, once your immune system has produced the appropriate B-cells and T-cells, it is able to remember information about an invading microbe. Should that microbe attack your body again in the future, your immune system is often better prepared and more able to fight off infection.

As mentioned before, this is but a mere introduction to the immune system. The details involved in any of these topics can easily fill entire textbooks. The human immune system is a fascinating and wonderfully complex model of organization. Without a functioning immune system, you wouldn’t last long in a world filled with potential bacteria and viruses.