Immune System: Diseases, Disorders & Function

The job of the immune system — which is a collection of structures and processes within the body — is to protect against disease or other potentially damaging foreign bodies. When functioning properly, the immune system identifies a variety of threats, including viruses, bacteria and parasites, and distinguishes them from the body’s own healthy tissue.

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. 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 contains white blood cells that fight infection or disease. 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 the bones produces white blood cells.

Lymphocytes: These small white blood cells play a large role in defending the body against disease. 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 sub-group 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.

Leukocytes: These white blood cells that identify and eliminate pathogens are the second arm of the innate immune system. The innate leukocytes include the phagocytes (macrophages, neutrophils, and dendritic cells), mast cells, eosinophils, basophils, and natural killer cells.

Diseases of the immune system

Disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer.

Immunodeficiency occurs when the immune system is not as strong as normal, resulting in recurring and life-threatening infections. 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.

Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, diabetes mellitus type 1 and systemic lupus erythematosus.

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.

While symptoms of immune diseases vary, fever and fatigue are common signs that the immune system is not functioning properly.

Treating 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. These conditions range from common to extremely rare, spanning all ages and encompassing various organ systems.

To become an allergist/immunologist, physicians must undergo three years of training in internal medicine or pediatrics after completing medical school and graduating with a medical degree. They must also pass the exam of either the American Board of Internal Medicine (ABIM) or the American Board of Pediatrics (ABP).

Internists and pediatricians must undergo at a two-year fellowship in an allergy/immunology training program to become an allergist/immunologist.

Some milestones in the history of immunology:

1718: Lady Mary Wortley Montagu, the wife of the British ambassador to Constantinople, observed the positive effects of variolation — the deliberate infection with the smallpox disease — on the native population and had the technique performed on her own children.

1796: Edward Jenner was the first to demonstrate the smallpox vaccine.

1840: Jakob Henle put forth the first modern proposal of the germ theory of disease.

1857-1870: The role of microbes in fermentation was confirmed by Louis Pasteur.

1880-1881: The theory that bacterial virulence could be used as vaccines was developed. Louis Pasteur put this theory in practice by experimenting with chicken cholera and anthrax vaccines. On May 5, 1881, Pasteur vaccinated 24 sheep, one goat, and six cows with five drops of the living attenuated anthrax bacillus.

1885: A 9-year-old Joseph Meister had been bitten by a rabid dog and was injected with the attenuated rabies vaccine by Pasteur. He is the first known human to survive rabies.

1886: American microbiologist Theobold Smith demonstrated that heat killed cultures of chicken cholera bacillus were also effective in protection from cholera.

1903: Maurice Arthus described the localizing allergic reaction called the Arthus response. 

1949: John Enders, Thomas Weller and Frederick Robbins experimented with the growth of polio virus in tissue culture, neutralization with immune sera, and demonstration of attenuation of neurovirulence with repetitive passage.

1951: Vaccine against yellow fever was developed.

1983: HIV was discovered by French virologist Luc Montagnier.

1986: Hepatitis B vaccine was produced by genetic engineering.

2005: Ian Frazer developed the human papillomavirus vaccine.

Related:

• Image Gallery: The BioDigital Human

Facts, Functions & Diseases:

• Circulatory System
• Digestive System
• Endocrine System
• Integumentary System (Skin)
• Lymphatic System
• Muscular System
• Nervous System
• Reproductive System
• Respiratory System
• Skeletal System
• Urinary System