Immune System Trivia
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98 free Immune System trivia questions with answers — science & nature quiz, new questions added Oct 2026.
This immune system trivia quiz covers the network of cells and molecules that keeps you alive in a world full of pathogens. The easy questions are the ones any biology student knows: which white blood cell is most abundant, where T cells get their name, what antibodies are made by, which organ filters blood and recycles old red cells, and what a vaccine actually does. From there it moves into the two-tier design of innate and adaptive immunity, phagocytosis, the four signs of inflammation, the complement cascade, and how the body tells self from non-self. The hard end covers immunology proper: killer versus helper T cells and their CD8 and CD4 co-receptors, MHC class I and II, the five antibody isotypes, IgE and Type I hypersensitivity, natural killer cells and missing self, toll-like receptors, thymic involution, why HIV targets CD4 cells and how fever is set in the hypothalamus. There is history too: Jenner and James Phipps, Metchnikoff's starfish larvae, Ehrlich's magic bullet, von Behring and Kitasato, and the discovery of interferon. Every answer was checked against Wikipedia's articles on the immune system, its cells, organs and pioneers, and each question links to the page that establishes it. Fifty questions, free, with an explanation after every answer.
30 of 98 questions with answers and explanations. Play the quiz
Q 01Unlike the innate system, what does the adaptive immune system do?
Learns to recognise molecules it has met before
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.
Q 02Which type of white blood cell is the most abundant in human blood?
Neutrophils
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.
Q 03The process by which immune cells engulf and digest pathogens is called what?
Phagocytosis
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.
Q 04Which Russian zoologist discovered how cells engulf invaders, in 1882, by sticking thorns into starfish larvae?
Élie Metchnikoff
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.
Q 05T cells get their name from which organ, where they mature?
Thymus
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.
Q 06Which hormone do auto-injector pens deliver to treat a severe allergic reaction?
Adrenaline
Adrenaline, also called epinephrine, raises blood pressure and relaxes the airways, countering anaphylaxis; that is why people with severe allergies carry an auto-injector.
Q 07In adults, lymphocytes derive from blood-forming stem cells in which tissue?
The bone marrow
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.
Q 08B cells drive which arm of adaptive immunity?
The humoral response
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.
Q 09When enough people are immune that a disease can no longer spread easily, the protection is called what?
Herd immunity
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.
Q 10Killer T cells release which molecule to breach a target cell's membrane?
Perforin
Perforin polymerises into pores in the target membrane; granzymes then enter through them and trigger apoptosis in the infected or cancerous cell.
Q 11Coeliac disease is an immune reaction to which protein?
Gluten
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.
Q 12What is the shape of a single antibody molecule?
Y-shaped
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.
Q 13In antibody names such as IgM, what does 'Ig' stand for?
Immunoglobulin
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.
Q 21Aspirin eases fever and inflammation by blocking the body's production of which signalling molecules?
Prostaglandins
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.
Q 22Fever results from a raised temperature set point in which part of the brain?
The hypothalamus
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.
Q 23Which cascade of blood proteins is named for helping antibodies to kill pathogens?
The complement system
Q 14Which antibody class is transported across the placenta from mother to fetus?
IgG
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.
Q 15Which antibody class mediates Type I hypersensitivity, the immediate reaction behind allergy and anaphylaxis?
IgE
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.
Q 16In 1890 Emil von Behring and which Japanese bacteriologist showed that immunised animals' serum neutralises diphtheria and tetanus toxins?
Kitasato Shibasaburō
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.
Q 17Antigens were originally so named because they are what?
Antibody generators
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.
Q 18Which lymphocytes kill infected and tumour cells with no earlier exposure needed?
Natural killer cells
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.
Q 19Hay fever is an allergic reaction to what?
Pollen
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.
Q 20What are the four classic symptoms of inflammation?
Redness, swelling, heat and pain
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.
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.
Q 24Coating a pathogen's surface with antibody to mark it for destruction is called what?
Opsonisation
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.
Q 25Who developed the injected polio vaccine that was declared safe and effective in April 1955?
Jonas Salk
Jonas Salk made his vaccine from killed virus rather than a weakened live one; he never patented it or earned money from it.
Q 26Toll-like receptors, which sense microbes, are named after a gene first found in which organism?
Drosophila fruit flies
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.
Q 27Dendritic cells, which present antigens to T cells, take their name from the Greek word for what?
Tree
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.
Q 28Which granulocyte, resident in connective tissue and mucous membranes, is most associated with allergy and anaphylaxis?
Mast cell
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.
Q 29Which organ, tucked under the left ribs, filters blood and removes old red blood cells?
The spleen
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.
Q 30Kupffer cells in the liver and microglia in the brain are tissue-resident forms of which cell?
Macrophage
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.