The immune system is a system of many biological structures and processes within an organism that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism’s own healthy tissue. In many species, the immune system can be classified into subsystems, such as the innate immune system versus the adaptive immune system, or humoral immunity versus cell-mediated immunity.
Inside your body there is an amazing protection mechanism called the immune system. It is designed to defend you against millions of bacteria, microbes, viruses, toxins and parasites that would love to invade your body. To understand the power of the immune system, all that you have to do is look at what happens to anything once it dies. That sounds gross, but it does show you something very important about your immune system.
When something dies, its immune system (along with everything else) shuts down. In a matter of hours, the body is invaded by all sorts of bacteria, microbes, parasites… None of these things are able to get in when your immune system is working, but the moment your immune system stops the door is wide open. Once you die it only takes a few weeks for these organisms to completely dismantle your body and carry it away, until all that’s left is a skeleton. Obviously your immune system is doing something amazing to keep all of that dismantling from happening when you are alive.
The immune system is complex, intricate and interesting. And there are at least two good reasons for you to know more about it. First, it is just plain fascinating to understand where things like fevers, hives, inflammation, etc., come from when they happen inside your own body. You also hear a lot about the immune system in the news as new parts of it are understood and new drugs come on the market — knowing about the immune system makes these news stories understandable. In this article, we will take a look at how your immune system works so that you can understand what it is doing for you each day, as well as what it is not.
Your immune system works around the clock in thousands of different ways, but it does its work largely unnoticed. One thing that causes us to really notice our immune system is when it fails for some reason. We also notice it when it does something that has a side effect we can see or feel. Here are several examples:
When you get a cut, all sorts of bacteria and viruses enter your body through the break in the skin. When you get a splinter you also have the sliver of wood as a foreign object inside your body. Your immune system responds and eliminates the invaders while the skin heals itself and seals the puncture. In rare cases the immune system misses something and the cut gets infected. It gets inflamed and will often fill with pus. Inflammation and pus are both side-effects of the immune system doing its job.
When a mosquito bites you, you get a red, itchy bump. That too is a visible sign of your immune system at work.
Each day you inhale thousands of germs (bacteria and viruses) that are floating in the air. Your immune system deals with all of them without a problem. Occasionally a germ gets past the immune system and you catch a cold, get the flu or worse. A cold or flu is a visible sign that your immune system failed to stop the germ. The fact that you get over the cold or flu is a visible sign that your immune system was able to eliminate the invader after learning about it. If your immune system did nothing, you would never get over a cold or anything else.
Each day you also eat hundreds of germs, and again most of these die in the saliva or the acid of the stomach. Occasionally, however, one gets through and causes food poisoning. There is normally a very visible effect of this breach of the immune system: vomiting and diarrhea are two of the most common symptoms.
There are also all kinds of human ailments that are caused by the immune system working in unexpected or incorrect ways that cause problems. For example, some people have allergies. Allergies are really just the immune system overreacting to certain stimuli that other people don’t react to at all. Some people have diabetes, which is caused by the immune system inappropriately attacking cells in the pancreas and destroying them. Some people have rheumatoid arthritis, which is caused by the immune system acting inappropriately in the joints. In many different diseases, the cause is actually an immune system error. Finally, we sometimes see the immune system because it prevents us from doing things that would be otherwise beneficial. For example, organ transplants are much harder than they should be because the immune system often rejects the transplanted organ.
The major components of the immune system include:
Lymph nodes: Small, bean-shaped structures that produce and store cells that fight infection and disease and are part of the lymphatic system — which consists of bone marrow, spleen, thymus and lymph nodes, according to “A Practical Guide To Clinical Medicine” from the University of California San Diego (UCSD). Lymph nodes also contain lymph, the clear fluid that carries those cells to different parts of the body. When the body is fighting infection, lymph nodes can become enlarged and feel sore.
Spleen: The largest lymphatic organ in the body, which is on your left side, under your ribs and above your stomach, contains white blood cells that fight infection or disease. According to the National Institutes of Health (NIH), the spleen also helps control the amount of blood in the body and disposes of old or damaged blood cells.
Bone marrow: The yellow tissue in the center of the bones produces white blood cells. This spongy tissue inside some bones, such as the hip and thigh bones, contains immature cells, called stem cells, according to the NIH. Stem cells, especially embryonic stem cells, which are derived from eggs fertilized in vitro (outside of the body), are prized for their flexibility in being able to morph into any human cell.
Lymphocytes: These small white blood cells play a large role in defending the body against disease, according to the Mayo Clinic. The two types of lymphocytes are B-cells, which make antibodies that attack bacteria and toxins, and T-cells, which help destroy infected or cancerous cells. Killer T-cells are a subgroup of T-cells that kill cells that are infected with viruses and other pathogens or are otherwise damaged. Helper T-cells help determine which immune responses the body makes to a particular pathogen.
Thymus: This small organ is where T-cells mature. This often-overlooked part of the immune system, which is situated beneath the breastbone (and is shaped like a thyme leaf, hence the name), can trigger or maintain the production of antibodies that can result in muscle weakness, the Mayo Clinic said. Interestingly, the thymus is somewhat large in infants, grows until puberty, then starts to slowly shrink and become replaced by fat with age, according to the National Institute of Neurological Disorders and Stroke.
Leukocytes: These disease-fighting white blood cells identify and eliminate pathogens and are the second arm of the innate immune system. A high white blood cell count is referred to as leukocytosis, according to the Mayo Clinic. The innate leukocytes include phagocytes (macrophages, neutrophils and dendritic cells), mast cells, eosinophils and basophils.
Diseases of the immune system
If immune system-related diseases are defined very broadly, then allergic diseases such as allergic rhinitis, asthma, and eczema are very common. However, these actually represent a hyper-response to external allergens, according to Dr. Matthew Lau, chief, department of allergy and immunology at Kaiser Permanente Hawaii. Asthma and allergies also involve the immune system. A normally harmless material, such as grass pollen, food particles, mold or pet dander, is mistaken for a severe threat and attacked.
Other dysregulation of the immune system includes autoimmune diseases such as lupus and rheumatoid arthritis. “Finally, some less common disease related to deficient immune system conditions are antibody deficiencies and cell mediated conditions that may show up congenitally,” Lau told Live Science.
Disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer, according to the NIH.
Immunodeficiency occurs when the immune system is not as strong as normal, resulting in recurring and life-threatening infections, according to the University of Rochester Medical Center. In humans, immunodeficiency can either be the result of a genetic disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS, or through the use of immunosuppressive medication.
On the opposite end of the spectrum, autoimmunity results from a hyperactive immune system attacking normal tissues as if they were foreign bodies, according to the University of Rochester Medical Center. Common autoimmune diseases include Hashimoto’s thyroiditis, rheumatoid arthritis, diabetes mellitus type 1 and systemic lupus erythematosus. Another disease considered to be an autoimmune disorder is myasthenia gravis (pronounced my-us-THEE-nee-uh GRAY-vis).
Diagnosing diseases of the immune system
Even though symptoms of immune diseases vary, fever and fatigue are common signs that the immune system is not functioning properly, the Mayo Clinic noted.
Most of the time, immune deficiencies are diagnosed with blood tests that either measure the level of immune elements or their functional activity, Lau said.
Allergic conditions may be evaluated using either blood tests or allergy skin testing to identify what allergens trigger symptoms.
How are immune deficiency diseases commonly treated?
In overactive or autoimmune conditions, medications that reduce the immune response, such as corticosteroids or other immune suppressive agents, can be very helpful. “In some immune deficiency conditions, the treatment may be replacement of missing or deficiency elements,” Lau said. “This may be infusions of antibodies to fight infections.”
Treatment may also include monoclonal antibodies, Lau said. A monoclonal antibody is a type of protein made in a lab that can bind to substances in the body. They can be used to regulate parts of the immune response that are causing inflammation, Lau said. According to the National Cancer Institute, monoclonal antibodies are being used to treat cancer. They can carry drugs, toxins or radioactive substances directly to cancer cells.
Who treats the immune system?
An allergist/immunologist is a physician specially trained to diagnose, treat and manage allergies, asthma and immunologic disorders, including primary immunodeficiency disorders, according to the American College of Asthma, Allergy and Immunology (ACAAI). These conditions range from common to extremely rare, spanning all ages and encompassing various organ systems.