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Immune system disorder, any of various failures in the body’s defense mechanisms against infectious organisms. Disorders of immunity include immune deficiency diseases, such as AIDS, that arise because of a diminution of some aspect of the immune response. Other types of immune disorders, such as allergies and autoimmune disorders, are caused when the body develops an inappropriate response to a substance—either to a normally harmless foreign substance found in the environment, in the case of allergies, or to a component of the body, in the case of autoimmune diseases. Lymphocytes (white blood cells of the immune system) can become cancerous and give rise to tumours called leukemias, lymphomas, and myelomas.

T cell infected with HIVFalse-colour scanning electron micrograph of a T cell infected with HIV (human immunodeficiency virus), the agent that causes AIDS (acquired immunodeficiency syndrome).
This article discusses various immune deficiencies, allergies, autoimmune disorders, and lymphocyte cancers. For additional information on leukemias, lymphomas, and myelomas, see the article cancer. A discussion of how the immune system works to prevent disease is found in the article immune system.
Immune deficiencies
Immune deficiency disorders result from defects that occur in immune mechanisms. The defects arise in the components of the immune system, such as the white blood cells involved in immune responses (T and B lymphocytes and scavenger cells) and the complement proteins, for a number of reasons. Some deficiencies are hereditary and result from genetic mutations that are passed from parent to child. Others are caused by developmental defects that occur in the womb. In some cases immune deficiencies result from damage inflicted by infectious agents. In others drugs used to treat certain conditions, or even the diseases themselves, can depress the immune system. Poor nutrition also can undermine the immune system. Limited contact with natural environmental factors, particularly with microorganisms found in biodiverse settings, also has been associated with increased risk of allergies, autoimmune disorders, and chronic inflammatory diseases.
Hereditary and congenital deficiencies
Immune deficiencies resulting from hereditary and congenital defects are rare, but they can affect all major aspects of the immune system. Luckily many of those conditions can be treated. In the rare hereditary disorder called X-linked infantile agammaglobulinemia, which affects only males, B lymphocytes are unable to secrete all classes of immunoglobulins. (An immunoglobulin is a type of protein, also called an antibody, that is produced by B cells in response to the presence of a foreign substance called an antigen.) The disease can be treated by periodic injections of large amounts of immunoglobulin G (IgG). The congenital, but not hereditary, T-cell deficiency disease called DiGeorge syndrome arises from a developmental defect occurring in the fetus that results in the defective development of the thymus. Consequently the infant has either no mature T cells or very few. In the most severe cases—i.e., when no thymus has developed—treatment of DiGeorge syndrome consists of transplantation of a fetal thymus into the infant. The group of disorders called severe combined immunodeficiency diseases result from a failure of precursor cells to differentiate into T or B cells. Bone marrow transplantation can successfully treat some of those diseases. The immune disorder called chronic granulomatous disease results from an inherited defect that prevents phagocytic cells from producing enzymes needed to break down ingested pathogens. Treatments include administration of a wide spectrum of antibiotics. Get a Britannica Premium subscription and gain access to exclusive content.
Deficiencies caused by infection
Damage to lymphocytes that is inflicted by viruses is common but usually transient. During infectious mononucleosis, for example, the Epstein-Barr virus infects B cells, causing them to express viral antigens. T cells that react against these antigens then attack the B cells, and a temporary deficiency in the production of new antibodies lasts until the overt viral infection has been overcome. Because antibodies already present in the blood are slowly broken down, failure to make new ones is important only if the infection persists for a long time, as it does occasionally. A much more serious viral infection is that caused by the human immunodeficiency virus (HIV), which is responsible for the fatal immune deficiency disease AIDS. HIV selectively infects helper T cells and prevents them from producing cytokines and from functioning in cell-mediated immunity. Persons with AIDS may be unable to overcome infections by a variety of microbes that are easily disposed of by persons uninfected with HIV. Severe infections by certain parasites, such as trypanosomes, also cause immune deficiency, as do some forms of cancer, but it is uncertain how that comes about. For example, Hodgkin disease, which attacks the lymphatic system, makes the patient more susceptible to infection.

Deficiencies caused by drug therapy
In countries with advanced medical services, immune deficiency often results from the use of powerful drugs to treat cancers. The drugs work by inhibiting the multiplication of rapidly dividing cells. Although the drugs act selectively on cancer cells, they also can interfere with the generation and multiplication of cells involved in immune responses. Prolonged or intensive treatment with such drugs impairs immune responses to some degree. Although the immune impairment is reversible, the physician must seek a balance between intentional damage to the cancer cells and unintentional damage to the immune system.
Medically induced suppression of the immune system also occurs when powerful drugs, which are designed to interfere with the development of T and B cells, are used to prevent the rejection of organ or bone marrow transplants or to damp down serious autoimmune responses. Although use of such drugs has greatly improved the success of transplants, it also leaves patients highly susceptible to microbial infections. Fortunately, most of those infections can be treated with antibiotics, but the immunosuppressive drugs have to be used with great care and for as short a period as possible.
Nutrition and Immunity

During the flu season or times of illness, people often seek special foods or vitamin supplements that are believed to boost immunity. Vitamin C and foods like citrus fruits, chicken soup, and tea with honey are popular examples. Yet the design of our immune system is complex and influenced by an ideal balance of many factors, not just diet, and especially not by any one specific food or nutrient. However, a balanced diet consisting of a range of vitamins and minerals, combined with healthy lifestyle factors like adequate sleep and exercise and low stress, most effectively primes the body to fight infection and disease.
What Is Our Immune System?
On a daily basis, we are constantly exposed to potentially harmful microbes of all sorts. Our immune system, a network of intricate stages and pathways in the body, protects us against these harmful microbes as well as certain diseases. It recognizes foreign invaders like bacteria, viruses, and parasites and takes immediate action. Humans possess two types of immunity: innate and adaptive.
Innate immunity is a first-line defense from pathogens that try to enter our bodies, achieved through protective barriers. These barriers include:
- Skin that keeps out the majority of pathogens
- Mucus that traps pathogens
- Stomach acid that destroys pathogens
- Enzymes in our sweat and tears that help create anti-bacterial compounds
- Immune system cells that attack all foreign cells entering the body
Adaptive or acquired immunity is a system that learns to recognize a pathogen. It is regulated by cells and organs in our body like the spleen, thymus, bone marrow, and lymph nodes. When a foreign substance enters the body, these cells and organs create antibodies and lead to multiplication of immune cells (including different types of white blood cells) that are specific to that harmful substance and attack and destroy it. Our immune system then adapts by remembering the foreign substance so that if it enters again, these antibodies and cells are even more efficient and quick to destroy it.
Other conditions that trigger an immune response
Antigens are substances that the body labels as foreign and harmful, which triggers immune cell activity. Allergens are one type of antigen and include grass pollen, dust, food components, or pet hair. Antigens can cause a hyper-reactive response in which too many white cells are released. People’s sensitivity to antigens varies widely. For example, an allergy to mold triggers symptoms of wheezing and coughing in a sensitive individual but does not trigger a reaction in other people.
Inflammation is an important, normal step in the body’s innate immune response. When pathogens attack healthy cells and tissue, a type of immune cell called mast cells counterattack and release proteins called histamines, which cause inflammation. Inflammation may generate pain, swelling, and a release of fluids to help flush out the pathogens. The histamines also send signals to discharge even more white blood cells to fight pathogens. However, prolonged inflammation can lead to tissue damage and may overwhelm the immune system.
Autoimmune disorders like lupus, rheumatoid arthritis, or type 1 diabetes are partly hereditary and cause hypersensitivity in which immune cells attack and destroy healthy cells.
Immunodeficiency disorders can depress or completely disable the immune system, and may be genetic or acquired. Acquired forms are more common and include AIDS and cancers like leukemia and multiple myeloma. In these cases, the body’s defenses are so reduced that a person becomes highly susceptible to illness from invading pathogens or antigens.
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What factors can depress our immune system?
- Older age: As we age, our internal organs may become less efficient; immune-related organs like the thymus or bone marrow produce less immune cells needed to fight off infections. Aging is sometimes associated with micronutrient deficiencies, which may worsen a declining immune function.
- Environmental toxins (smoke and other particles contributing to air pollution, excessive alcohol): These substances can impair or suppress the normal activity of immune cells.
- Excess weight: Obesity is associated with low-grade chronic inflammation. Fat tissue produces adipocytokines that can promote inflammatory processes. [1] Research is early, but obesity has also been identified as an independent risk factor for the influenza virus, possibly due to the impaired function of T-cells, a type of white blood cell. [2]
- Poor diet: Malnutrition or a diet lacking in one or more nutrients can impair the production and activity of immune cells and antibodies.
- Chronic diseases: Autoimmune and immunodeficiency disorders attack and potentially disable immune cells.
- Chronic mental stress: Stress releases hormones like cortisol that suppresses inflammation (inflammation is initially needed to activate immune cells) and the action of white blood cells.
- Lack of sleep and rest: Sleep is a time of restoration for the body, during which a type of cytokine is released that fights infection; too little sleep lowers the amount of these cytokines and other immune cells.
Does an Immune-Boosting Diet Exist?
Eating enough nutrients as part of a varied diet is required for the health and function of all cells, including immune cells. Certain dietary patterns may better prepare the body for microbial attacks and excess inflammation, but it is unlikely that individual foods offer special protection. Each stage of the body’s immune response relies on the presence of many micronutrients. Examples of nutrients that have been identified as critical for the growth and function of immune cells include vitamin C, vitamin D, zinc, selenium, iron, and protein (including the amino acid glutamine). [3,4] They are found in a variety of plant and animal foods.

Diets that are limited in variety and lower in nutrients, such as consisting primarily of ultra-processed foods and lacking in minimally processed foods, can negatively affect a healthy immune system. It is also believed that a Western diet high in refined sugar and red meat and low in fruits and vegetables can promote disturbances in healthy intestinal microorganisms, resulting in chronic inflammation of the gut, and associated suppressed immunity. [5]
The microbiome is an internal metropolis of trillions of microorganisms or microbes that live in our bodies, mostly in the intestines. It is an area of intense and active research, as scientists are finding that the microbiome plays a key role in immune function. The gut is a major site of immune activity and the production of antimicrobial proteins. [6,7] The diet plays a large role in determining what kinds of microbes live in our intestines. A high-fiber plant-rich diet with plenty of fruits, vegetables, whole grains, and legumes appear to support the growth and maintenance of beneficial microbes. Certain helpful microbes break down fibers into short chain fatty acids, which have been shown to stimulate immune cell activity. These fibers are sometimes called prebiotics because they feed microbes. Therefore, a diet containing probiotic and prebiotic foods may be beneficial. Probiotic foods contain live helpful bacteria, and prebiotic foods contain fiber and oligosaccharides that feed and maintain healthy colonies of those bacteria.
- Probiotic foods include kefir, yogurt with live active cultures, fermented vegetables, sauerkraut, tempeh, kombucha tea, kimchi, and miso.
- Prebiotic foods include garlic, onions, leeks, asparagus, Jerusalem artichokes, dandelion greens, bananas, and seaweed. However, a more general rule is to eat a variety of fruits, vegetables, beans, and whole grains for dietary prebiotics.

Chicken soup as medicine?
A warm bowl of chicken soup is a popular go-to when we’re feeling under the weather. Is there scientific evidence that it aids in healing? The short answer is no; there aren’t any clinical trials that show that chicken soup speeds healing any more than other foods. But when breaking down its ingredients, it does appear a worthwhile remedy to try. First of all, chicken soup is light and easy on the stomach when our appetite isn’t great. Second, it provides fluids and electrolytes to prevent dehydration, which can easily occur with a fever. Lastly, a traditional chicken soup recipe supplies various nutrients involved in the immune system: protein and zinc from the chicken, vitamin A from carrots, vitamin C from celery and onions, and antioxidants in the onions and herbs. This is one tasty and soothing food to include when not feeling well and doesn’t need a doctor’s prescription.
Do Vitamin or Herbal Supplements Help?
A deficiency of single nutrients can alter the body’s immune response. Animal studies have found that deficiencies in zinc, selenium, iron, copper, folic acid, and vitamins A, B6, C, D, and E can alter immune responses. [8] These nutrients help the immune system in several ways: working as an antioxidant to protect healthy cells, supporting growth and activity of immune cells, and producing antibodies. Epidemiological studies find that those who are poorly nourished are at greater risk of bacterial, viral, and other infections.

Spotlight on vitamin D
Vitamin D’s role in regulating the immune system has led scientists to explore two parallel research paths: Does vitamin D deficiency contribute to the development of multiple sclerosis, type 1 diabetes, and other so-called “autoimmune” diseases, where the body’s immune system attacks its own organs and tissues? And could vitamin D supplements help boost our body’s defenses to fight infectious disease, such as tuberculosis and seasonal flu?
Eating a good quality diet, as depicted by the Healthy Eating Plate, can prevent deficiencies in these nutrients. However, there are certain populations and situations in which one cannot always eat a variety of nutritious foods, or who have increased nutrient needs. In these cases a vitamin and mineral supplement may help to fill nutritional gaps. Studies have shown that vitamin supplementation can improve immune responses in these groups. [8-10] Low-income households, pregnant and lactating women, infants and toddlers, and the critically ill are examples of groups at risk.
The elderly are a particularly high-risk group. The immune response generally declines with increasing age as the number and quality of immune cells decreases. This causes a higher risk of poorer outcomes if the elderly develop chronic or acute diseases. In addition, about one-third of elderly in industrialized countries have nutrient deficiencies. [8] Some reasons include a poorer appetite due to chronic diseases, depression, or loneliness; multiple medications that can interfere with nutrient absorption and appetite; malabsorption due to intestinal issues; and increased nutrient needs due to hypermetabolic states with acute or chronic conditions. Diet variety may also be limited due to budget constraints or lower interest in cooking for one person; poor dentition; mental impairment; or lack of transportation and community resources to obtain healthy food.
A general multivitamin/mineral supplement providing the recommended dietary allowances (RDA) may be used in these cases, unless otherwise directed by one’s physician. Megadose supplements (many times the RDA) do not appear justified, and can sometimes be harmful or even suppress the immune system (e.g., as with zinc). Remember that vitamin supplements should not be considered a substitute for a good diet because no supplements contain all the benefits of healthful foods.
Herbals
Several herbal supplements have been suggested to boost immune function. What does the research say?
- Echinacea: Cell studies have shown that echinacea can destroy influenza viruses, but limited research in humans has been inconclusive in determining echinacea’s active components. Taking echinacea after catching a cold has not been shown to shorten its duration, but taking it while healthy may offer a small chance of protection from catching a cold. [11,12]
- Garlic: The active ingredient in garlic, allicin sativum, is proposed to have antiviral and antimicrobial effects on the common cold, but high-quality clinical trials comparing garlic supplements to placebo are lacking. A Cochrane review identified only one trial of reasonable quality following 146 participants. Those taking the garlic supplement for 3 months had fewer occurrences of the common cold than those taking a placebo, but after contracting the cold virus, both groups had a similar duration of illness. [13] Note that these findings are from a single trial, which needs to be replicated.
- Tea catechins: Cell studies have shown that tea catechins such as those found in green tea can prevent flu and some cold viruses from replicating and can increase immune activity. Human trials are still limited. Two randomized controlled trials found that green tea capsules produced less cold/flu symptoms or incidence of flu than a placebo; however both studies were funded or had author affiliations with tea industries. [14]
8 Steps to Help Support a Healthy Immune System
- Eat a balanced diet with whole fruits, vegetables, lean proteins, whole grains, and plenty of water. A Mediterranean Diet is one option that includes these types of foods.
- If a balanced diet is not readily accessible, taking a multivitamin containing the RDA for several nutrients may be used.
- Don’t smoke (or stop smoking if you do).
- Drink alcohol in moderation.
- Perform moderate regular exercise.
- Aim for 7-9 hours of sleep nightly. Try to keep a sleep schedule, waking up and going to bed around the same time each day. Our body clock, or circadian rhythm, regulates feelings of sleepiness and wakefulness, so having a consistent sleep schedule maintains a balanced circadian rhythm so that we can enter deeper, more restful sleep.
- Aim to manage stress. This is easier said than done, but try to find some healthy strategies that work well for you and your lifestyle—whether that be exercise, meditation, a particular hobby, or talking to a trusted friend. Another tip is to practice regular, conscious breathing throughout the day and when feelings of stress arise. It doesn’t have to be long—even a few breaths can help. If you’d like some guidance, try this short mindful breathing exercise.
- Wash hands throughout the day: when coming in from outdoors, before and after preparing and eating food, after using the toilet, after coughing or blowing your nose.
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