98 Fun Facts About Immune System

Unlike the innate system, what does the adaptive immune system do?

The adaptive system learns to recognise molecules it has met before, building immunological memory through B and T cells; that memory is the basis of vaccination.

Which type of white blood cell is the most abundant in human blood?

Neutrophils are the most abundant white blood cells and among the first to reach an infection; they swallow microbes and die in such numbers that their remains form pus.

The process by which immune cells engulf and digest pathogens is called what?

Phagocytosis traps the pathogen in a phagosome that fuses with a lysosome to digest it; single-celled amoebae use the same trick simply to eat.

Which Russian zoologist discovered how cells engulf invaders, in 1882, by sticking thorns into starfish larvae?

Élie Metchnikoff saw mobile cells crowd around the thorns and reasoned that they defend the body by devouring invaders; the idea won him a share of the 1908 Nobel Prize.

T cells get their name from which organ, where they mature?

Thymus gives T cells their name: they go there to be tested against the body's own proteins, and only about 2% leave as mature T cells; the rest die.

Which hormone do auto-injector pens deliver to treat a severe allergic reaction?

Adrenaline, also called epinephrine, raises blood pressure and relaxes the airways, countering anaphylaxis; that is why people with severe allergies carry an auto-injector.

In adults, lymphocytes derive from blood-forming stem cells in which tissue?

The bone marrow makes every lymphocyte from blood-forming stem cells; B cells also mature there, while T cells must travel to a second organ to finish maturing.

B cells drive which arm of adaptive immunity?

The humoral response is named after the humours, the old word for body fluids: activated B cells become plasma cells that pump antibodies into the bloodstream, while T cells attack infected cells directly.

When enough people are immune that a disease can no longer spread easily, the protection is called what?

Herd immunity shields people who can't be vaccinated, such as newborns too young for their shots: with enough immune people around them, an infection runs out of routes to reach them.

Killer T cells release which molecule to breach a target cell's membrane?

Perforin polymerises into pores in the target membrane; granzymes then enter through them and trigger apoptosis in the infected or cancerous cell.

Coeliac disease is an immune reaction to which protein?

Gluten, found in wheat, barley and rye, makes the immune system of people with coeliac disease attack the lining of their own small intestine, so nutrients are poorly absorbed; the treatment is a lifelong gluten-free diet.

What is the shape of a single antibody molecule?

An antibody is Y-shaped: two variable arm tips bind antigen, while the tail, or Fc region, is far less variable and engages other immune cells.

In antibody names such as IgM, what does 'Ig' stand for?

Immunoglobulin is the formal name for an antibody, and the last letter names the class: IgM is usually the first made in a new infection, before B cells switch to making other classes.

Which antibody class is transported across the placenta from mother to fetus?

IgG is actively carried across the placenta by the neonatal Fc receptor, giving babies their mother's range of antigen specificities; colostrum then supplies more antibodies to the gut.

Which antibody class mediates Type I hypersensitivity, the immediate reaction behind allergy and anaphylaxis?

IgE is the rarest antibody class in blood and is thought to have evolved to fight parasitic worms; in allergy it is aimed at harmless things such as shrimp or cat dander.

In 1890 Emil von Behring and which Japanese bacteriologist showed that immunised animals' serum neutralises diphtheria and tetanus toxins?

Kitasato Shibasaburō shared the 1890 discovery that led to antitoxin serum for diphtheria, yet when the first Nobel Prize in Medicine was awarded in 1901 it went to von Behring alone.

Antigens were originally so named because they are what?

Antibody generators is what the name means: the word was coined in 1899 from anti(body) and -gen, and now covers anything the immune system can target, from a flu virus to a peanut protein.

Which lymphocytes kill infected and tumour cells with no earlier exposure needed?

Natural killer cells look for 'missing self': healthy cells display an identity marker called MHC I, and a cell that a virus or tumour has stripped of it is treated as a threat and destroyed.

Hay fever is an allergic reaction to what?

Pollen, the fine powder that plants release, sets off hay fever when the immune system mistakes it for a threat; the inflammation that follows in the nose and eyes causes the sneezing and itching.

What are the four classic symptoms of inflammation?

Redness, swelling, heat and pain, Celsus's rubor, tumor, calor and dolor, come from increased blood flow and leaky vessels driven by eicosanoids and cytokines from injured cells.

Aspirin eases fever and inflammation by blocking the body's production of which signalling molecules?

Prostaglandins raise body temperature and widen blood vessels in inflammation; John Vane showed in 1971 that aspirin works by stopping the body making them, which won him a share of the 1982 Nobel Prize.

Fever results from a raised temperature set point in which part of the brain?

Pyrogens raise the hypothalamus's temperature set point, producing fever; hyperthermia, by contrast, is a rise above an unchanged set point and does not respond to antipyretics.

Which cascade of blood proteins is named for helping antibodies to kill pathogens?

The complement system is a chain of blood proteins that switch one another on in sequence; the last of them assemble into the membrane attack complex, which punches a hole in the microbe.

Coating a pathogen's surface with antibody to mark it for destruction is called what?

Opsonisation tags the microbe: engulfing cells carry receptors that grip the tail of each bound antibody, so a coated bacterium is swallowed far more readily than a bare one.

Who developed the injected polio vaccine that was declared safe and effective in April 1955?

Jonas Salk made his vaccine from killed virus rather than a weakened live one; he never patented it or earned money from it.

Toll-like receptors, which sense microbes, are named after a gene first found in which organism?

Drosophila fruit flies carry the Toll gene, first known for shaping the embryo; in 1996 Jules Hoffmann's team showed that flies without it die of infections, work that won a share of the 2011 Nobel Prize.

Dendritic cells, which present antigens to T cells, take their name from the Greek word for what?

Tree is the meaning of the Greek dendron: Ralph Steinman named the cells in 1973 for their branching arms, and he died three days before his 2011 Nobel Prize for the discovery was announced.

Which granulocyte, resident in connective tissue and mucous membranes, is most associated with allergy and anaphylaxis?

Mast cells are packed with granules of histamine, which they release rapidly on meeting an allergen; the flood widens blood vessels and causes the itching, swelling and, at worst, the collapse of anaphylaxis.

Which organ, tucked under the left ribs, filters blood and removes old red blood cells?

The spleen recycles iron from worn-out red cells and holds a reserve of blood; people can live without one, though they are left more prone to certain infections.

Kupffer cells in the liver and microglia in the brain are tissue-resident forms of which cell?

Macrophage means 'large eater': these cells settle in every organ under local names, from Kupffer cells in the liver to microglia in the brain, and swallow microbes, debris and worn-out cells.

HIV specifically infects which immune population, whose depletion defines AIDS?

CD4+ helper T lymphocytes direct the rest of the immune response, so as HIV destroys them the body loses to infections it would normally shrug off; AIDS is diagnosed when their count falls below 200 per cubic millimetre.

The 'swollen glands' felt in the neck during a cold are actually what?

Lymph nodes swell near an infection because that is where the fight is organised: immune cells that recognise the invader gather and multiply inside the nearest nodes.

What is the most common cause of immunodeficiency in developing countries?

Malnutrition is the leading cause of immunodeficiency worldwide: diets short of protein weaken immune cells and antibody production.

Which of these is a common autoimmune disease?

Hashimoto's thyroiditis is the immune system slowly destroying the thyroid gland; once the gland can no longer make enough hormone, patients take a daily replacement tablet, levothyroxine.

Which autoimmune disease destroys insulin-making cells?

Type 1 diabetes begins when the immune system mistakenly attacks cells in the pancreas; once they are gone the body can no longer make insulin, so patients need injections or a pump to survive.

For his 1796 experiment, Edward Jenner took pus from the hand of Sarah Nelmes, who worked as what?

A milkmaid, Sarah Nelmes, supplied the pus that Jenner scratched into James Phipps, his gardener's eight-year-old son; weeks later he exposed the boy to smallpox itself, and no disease followed.

The word vaccine derives from Variolae vaccinae, Jenner's Latin term for what?

Cowpox gave vaccines their name: Jenner's Variolae vaccinae meant 'smallpox of the cow', from the Latin vacca, the mild disease whose pus protected people against the deadly one.

Which two diseases were declared eradicated worldwide in 1980 and 2011 respectively?

Smallpox and rinderpest are the only two diseases ever eradicated, as of 2025; rinderpest, the 'cattle plague', never infected people at all, killing cattle and buffalo instead.

Who made the first rabies vaccine, given in 1885 to a boy who had been mauled by a rabid dog?

Louis Pasteur agreed, with some reluctance, to try his vaccine on nine-year-old Joseph Meister, who faced near-certain death; the boy lived, and public donations then funded the Institut Pasteur.

Which signalling proteins do virus-infected cells release to warn their neighbours to raise antiviral defences?

Interferons are named for 'interfering' with viruses: Alick Isaacs and Jean Lindenmann found them in London in 1957 while studying how one viral infection can block a second.

Which Greek historian recorded that plague survivors could nurse the sick without catching it again?

Thucydides caught the Plague of Athens himself and survived to describe it; his remark that the same person was never attacked twice is among the earliest accounts of acquired immunity.

Which enzyme found in saliva, tears and breast milk acts as an antibacterial chemical barrier?

Lysozyme was found by Alexander Fleming in nasal mucus, years before he discovered penicillin; it breaks open bacterial cell walls, which is why tears and saliva are mildly antiseptic.

When a B or T cell meets its matching antigen and multiplies, the process is called what?

Clonal selection, proposed by Macfarlane Burnet in 1957, expands the one lineage whose receptor fits the antigen; each B cell lineage carries a different antibody, so together they cover every antibody the body can make.

Protection borrowed from a mother's antibodies, via the placenta or breast milk, is what kind of immunity?

Passive immunity lasts from a few days to several months because the infant receives ready-made antibodies and makes no memory cells of its own.

The autoimmune disease lupus takes its name from the Latin word for which animal?

Wolf is lupus in Latin: medieval doctors gave the name to ulcerating skin diseases, apparently because they seemed to devour the flesh; today's lupus often shows as a butterfly-shaped rash across the face.

MHC molecules, the cell-surface identity tags that T cells read, were first found through research into what?

Organ and tissue transplants revealed the MHC: George Snell bred mouse strains that differed only in whether they rejected each other's grafts, and its full name, major histocompatibility complex, means tissue compatibility.

Which trio of side effects limits long-term use of steroid drugs such as prednisolone?

Central obesity, hyperglycaemia and osteoporosis arise because these drugs mimic cortisol, the body's own stress hormone, which in excess moves fat to the trunk, raises blood sugar and thins the bones.

The 2018 Nobel Prize in Medicine honoured the discovery that releasing the immune system's 'brakes' lets it attack what?

Cancer cells exploit proteins that act as brakes on T cells; James Allison and Tasuku Honjo showed that blocking those brakes frees the immune system to attack tumours, a therapy first proven in advanced melanoma.

Which big cat is so genetically uniform that unrelated animals accept each other's skin grafts?

Cheetah skin grafts heal as if donor and recipient were clones, because two population crashes, about 100,000 and 12,000 years ago, stripped the species of genetic variety.

Which gene-editing tool began as a bacterial defence that stores DNA from past viral invaders?

CRISPR is how bacteria keep mugshots of viruses: they file away scraps of an attacker's DNA and use them to guide cutting enzymes at the next attack. Scientists borrowed that targeting trick to edit genes.

Which sea creature's bright blue blood is harvested to test injectable drugs for bacterial toxins?

Horseshoe crab blood cells clot the moment they meet a trace of bacterial toxin, an ancient immune defence that labs use as a contamination alarm. The blood is blue because it carries oxygen with copper instead of iron.

A bite from the lone star tick can leave a person's immune system allergic to which food?

Red meat turns dangerous because the bite primes the body against alpha-gal, a sugar found in beef, pork and lamb. Unusually for a food allergy, the reaction starts hours after the meal, not within minutes.

In 2022 Maryland surgeons gave a living patient a gene-edited heart from which animal?

Pig organs are normally destroyed on sight, so the donor animal carried ten genetic modifications to slip past the patient's immune system. A baboon heart given to "Baby Fae" in 1984 kept her alive for only three weeks.

Which pouch off the large intestine, long dismissed as useless, may shelter helpful gut bacteria?

Appendix walls hold a reserve of friendly microbes that can repopulate the gut after a bout of diarrhoea flushes the rest away. Charles Darwin had guessed it was a leftover from ancestors who digested fibrous plants.

Most influenza vaccines have traditionally been grown inside which everyday food item?

Chicken eggs, fertilised and incubated, have served as virus factories since Ernest Goodpasture's team showed in 1931 that viruses multiply inside them. The shots are considered safe even for people with egg allergies.

Which general, scarred by a pox caught in Barbados as a teenager, ordered his whole army inoculated?

George Washington knew the risk first-hand: the bout he survived in Barbados left his face slightly scarred but protected him for life. Variolation meant deliberately giving healthy soldiers a mild dose.

The 'positive' in a blood type such as A positive refers to a factor named after which animal?

Rhesus monkey red cells were used to raise the first test serum, so the factor became Rh. A mismatch matters most in pregnancy, when a mother who lacks the factor can make antibodies against her baby's blood.

Which childhood virus can wipe the body's memory of past infections, a loss called immune amnesia?

Measles kills the cells that hold antibody memories, leaving survivors open for up to three years to diseases they had already beaten. Vaccination prevents the wipe.

Jonas Salk, hailed as a miracle worker in 1955, never patented his vaccine against which disease?

Polio shots made Salk a hero, yet he sought no profit so the vaccine could spread worldwide. Asked on television who owned the patent, he replied: "Could you patent the sun?"

Louis Pasteur's 1885 vaccine, first given to a boy mauled by a dog, protected against which disease?

Rabies was a death sentence until nine-year-old Joseph Meister received a course of 13 injections and stayed healthy. Each dose used virus that had been weakened for a shorter time than the one before.

The chickenpox virus can lie dormant in nerves for decades, then return as which painful rash?

Shingles strikes when ageing or weakened immune defences let the dormant virus travel back down a nerve to the skin. Its name comes from the Latin for girdle, after the band the rash forms on one side of the body.

Which autoimmune disease is known for a butterfly-shaped rash across the nose and cheeks?

Lupus is Latin for wolf, a medieval name for skin ulcers said to resemble a wolf's bite. In the disease the immune system mistakenly attacks healthy tissue in many parts of the body.

In type 1 diabetes, the immune system destroys the pancreatic cells that make which hormone?

Insulin runs out because the body's own defences wipe out the beta cells of the pancreas, the only cells that make it. What sets off the attack remains unclear.

B cells are named after the bursa of Fabricius, an organ found in which group of animals?

Birds mature these antibody-making cells in the bursa, a small pouch off the cloaca that mammals lack. The organ honours Hieronymus Fabricius, the anatomist who described it in 1621.

Which Russian empress was inoculated by English doctor Thomas Dimsdale, then made him a baron?

Catherine the Great kept a relay of horses ready to rush Dimsdale out of Russia if the procedure went badly. It worked, and he went on to treat her son and more than 140 members of the court.

Which chemical, blocked by hay fever tablets, triggers the itching and sneezing of an allergy?

Histamine waits ready-made inside immune cells and floods out when they meet an allergen. Older hay fever tablets also blocked it in the brain, which is why they caused drowsiness.

Katalin Karikó and Drew Weissman's 2023 Nobel Prize honoured vaccine work on which molecule?

Messenger RNA set off inflammation when injected, until the pair showed from 2005 that modified building blocks slipped past the body's alarms. Karikó's university had demoted her in 1995 after repeated grant rejections.

The 'P' in the childhood DTaP vaccine stands for pertussis, an infection better known by which name?

Whooping cough is also called the 100-day cough, because its violent coughing fits can drag on for ten weeks or more. The whoop is the high-pitched gasp as the sufferer finally breathes in.

Which deadly condition arises when the body's response to an infection damages its own organs?

Sepsis is harm done by the body's own runaway defences, not directly by the microbe. Hippocrates introduced the word in the 4th century BC, when it meant the rotting of organic matter.

Linus Pauling, winner of two Nobel Prizes, claimed megadoses of which nutrient could prevent colds?

Vitamin C became a health craze after Pauling's 1970 book Vitamin C and the Common Cold. He had won his Nobel Prizes for chemistry and for peace, not for medicine.

The first successful kidney transplant, in 1954, avoided rejection as donor and patient were what?

Identical twins share the same tissue markers, so Richard Herrick's body accepted brother Ronald's kidney as its own. Surgeon Joseph Murray won a Nobel Prize in 1990 for the work.

Which blood type is called the universal donor because its red cells lack the main antigens?

O negative red cells carry neither the A, the B nor the D marker, leaving a recipient's antibodies nothing to attack. Guidelines keep it for O negative patients, women who may be pregnant and emergencies with no time for testing.

Which stress hormone, released by glands above the kidneys, dampens the immune system?

Cortisol is so good at calming immune reactions that, sold as hydrocortisone, it is the cream people rub on rashes and eczema. One of its natural jobs is to suppress the immune system.

Drug names ending in '-mab', such as adalimumab, mark which kind of laboratory-made immune protein?

Monoclonal antibody drugs trace back to 1975, when Georges Köhler and César Milstein fused antibody-making cells with tumour cells to create immortal factories for a single antibody. The 'mab' is simply the abbreviation.

What name is given to the antibody-rich first milk that mothers produce in the days after birth?

Colostrum is a matter of life and death on farms: calves denied it almost always die of bacterial infection. Human babies are less dependent on it, having received their mother's antibodies before birth.

Which part of the eye can be transplanted from a donor with far less risk of rejection than skin?

Cornea grafts survive long-term in 50 to 90 percent of cases, while skin from a stranger is rejected almost every time. Such privilege is thought to shield vital structures from the damage inflammation would do.

David Strachan's 1989 idea that too few childhood infections lead to allergies goes by what name?

Hygiene hypothesis thinking began with the observation that hay fever and eczema were rarer in children from larger families. Strachan argued that siblings pass on the infections a young immune system needs.

David Vetter, the 'bubble boy' who lived 12 years in sterile plastic chambers, had which disorder?

Severe combined immunodeficiency dramatically weakens the immune system, so he lived behind plastic from birth. In 1977 NASA engineers built him a spacesuit for walks outside, which he outgrew after a few outings.

Early Chinese inoculators blew powdered scabs through a silver pipe into which part of the body?

Nostril choice followed a rule: the right for boys, the left for girls. Donors were picked from mild cases, in the hope of a gentle illness that nonetheless left the patient protected.

The word 'immune' comes from the Latin immunis, which described a citizen exempt from what?

Public service was a burden citizens owed, and anyone excused from it was immunis, literally "not paying a share". The medical sense, exempt from a disease, is attested only from 1881.

Which mosquito-borne virus can be worse the second time, as old antibodies help it enter cells?

Dengue comes in several types, and antibodies raised against one can grip another without disarming it, carrying the virus into immune cells instead. The effect is called antibody-dependent enhancement.

Nanobodies, tiny antibody fragments used in drugs, were first made from antibodies of which animals?

Camels, llamas and alpacas make antibodies with no light chains, so the binding tip is one small unit that can be cut free. That fragment reaches hidden targets a whole antibody cannot.

Which disease is the target of RTS,S, the first vaccine ever licensed against a human parasite?

Malaria vaccine RTS,S is a hybrid: genes from the parasite's outer coat joined to a piece of hepatitis B virus. The antibodies it raises block the parasite before it can infect the liver.

Which drug, made by a fungus found in Norwegian soil, transformed organ transplants in the 1980s?

Ciclosporin came from a fungus that Sandoz employees isolated from a Norwegian soil sample, and won US approval in 1983. It works by lowering the activity of T cells, which lead the attack on a new organ.

Which oily compound in poison ivy triggers the itchy rash, a delayed immune reaction?

Urushiol takes its name from urushi, the Japanese lacquer tree, whose sap carries the same irritant and hardens into the gloss on traditional lacquerware. The rash is the work of T cells, not of the oil itself.

What name is given to the precise patch of an antigen that an antibody recognises and binds?

Epitope and paratope are the two halves of a handshake: the paratope is the matching tip on the antibody. Immunologists also call the epitope an antigenic determinant.

What term describes white blood cells homing in on an infection by following chemical signals?

Chemotaxis lets a defender crawl toward the highest concentration of molecules shed at the scene of an injury or infection. Bacteria use the same trick to swim toward food and away from poisons.

Which white blood cell, named for the red dye that stains it, specialises in fighting parasites?

Eosinophil granules soak up eosin, a red dye, and turn brick-red under the microscope. Their contents are toxic to a parasitic worm, though they harm the host's own tissue as well.

Which British biologist's wartime skin-graft work led to a 1960 Nobel Prize for immune tolerance?

Peter Medawar showed that a mouse exposed to another strain's cells very early in life would later accept that strain's skin as its own. He shared the prize with Australian Macfarlane Burnet, who had predicted the effect.

Which scientist won a 2011 Nobel Prize for discovering dendritic cells three days after his death?

Ralph Steinman had died on 30 September, and the committee announced his prize without knowing. Nobel rules bar posthumous awards, but the foundation let it stand because the choice was made in good faith.

Which enslaved African man taught Boston minister Cotton Mather the practice of inoculation?

Onesimus described how a needle dipped in a sufferer's pustule was scraped across a healthy person's skin. When an epidemic struck in 1721, Mather promoted the method and physician Zabdiel Boylston carried it out.

Which American developed over 40 vaccines, including a mumps shot cultured from his sick daughter?

Maurice Hilleman cultured the virus from his daughter Jeryl Lynn when she caught mumps in 1963, and the strain named after her went into the combined MMR vaccine he also developed.

What name is given to an ingredient, such as an aluminium salt, that boosts a vaccine's effect?

Adjuvant comes from the Latin adiuvare, to help. Alum was the first aluminium salt used this way, though vaccine makers have largely replaced it with aluminium hydroxide and aluminium phosphate.

The BCG vaccine, bred from a cattle bacterium and first used in 1921, guards against which disease?

Tuberculosis in cattle is caused by a close cousin of the human germ, and BCG is a live strain of it that has lost the power to cause disease in people. The letters stand for Bacillus Calmette–Guérin, after its French creators.

In multiple sclerosis, the immune system attacks which fatty insulating layer around nerve fibres?

Myelin damage leaves scars along the brain and spinal cord, and those scars, or sclerae, give multiple sclerosis its name. The disease usually begins between the ages of 20 and 40.

What thick, whitish-yellow fluid at an infection site is made largely of dead white blood cells?

Pus is mostly the bodies of white blood cells that died fighting, suspended in a thin, protein-rich fluid. It sometimes turns green because some of those cells make an intensely green antibacterial protein.

Antibodies are also known by which name, shortened to Ig in the labels of their different classes?

Immunoglobulins come in two forms: anchored on the surface of a B cell as its sensor, or released into the blood, where they are usually just called antibodies.

Which Austrian physician won a 1930 Nobel Prize for discovering the ABO blood groups?

Karl Landsteiner noticed in 1900 that blood from two people often clumped when mixed, and by the next year had traced the effect to substances in the serum, which let him sort people into groups.