The Immune System

How the Immune system keeps you alive

Immune System:

The role of the immune system - 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, according to Merck Manuals.

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.

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.

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, according to the ACAAI. 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 a two-year fellowship in an allergy/immunology training program to become an allergist/immunologist, the ACAAI said.

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. Pasteur put this theory into 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 live attenuated anthrax bacillus.

1885: Joseph Meister, 9 years old, was injected with the attenuated rabies vaccine by Pasteur after being bitten by a rabid dog. He is the first known human to survive rabies.

1886: American microbiologist Theobold Smith demonstrated that heat-killed cultures of chicken cholera bacillus were effective in protecting against cholera.

1903: Maurice Arthus described the localizing allergic reaction that is now known as 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 (human immunodeficiency virus) was discovered by French virologist Luc Montagnier.

1986: Hepatitis B vaccine was produced by genetic engineering.

2005: Ian Frazer developed the human papillomavirus vaccine.