50 Fun Facts About Immune System

The immune system has two major subsystems. The innate system gives a preconfigured response; what does the other, adaptive system do?

Its immunological memory is the basis of vaccination.

Which type of white blood cell is the most abundant, making up 50-70% of leukocytes?

Roughly 100 billion are produced each day and they live only 5 to 135 hours.

The process by which cells such as macrophages engulf and digest pathogens is called what?

The engulfed pathogen is trapped in a phagosome that fuses with a lysosome; it is probably the oldest form of host defence.

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

Working in a private lab in Messina, Sicily, he watched unusual cells surround the thorns; he is called the father of innate immunity.

The 1908 Nobel Prize in Physiology or Medicine went jointly to the founder of cellular immunology and which German scientist, author of the side-chain theory?

Ehrlich also coined the "magic bullet" idea and discovered Salvarsan, the first drug aimed at a specific pathogen.

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

Developing T cells migrate there and are stimulated by thymosin.

The organ where T cells mature reaches its maximum size at puberty and then shrinks in a process called what?

It can weigh 40-50 grams at its peak.

Lymphocytes derive from haematopoietic stem cells in which tissue?

Human marrow turns out about 500 billion blood cells a day.

B cells are responsible for which arm of adaptive immunity?

T cells handle cell-mediated immunity; activated B cells become plasma cells pumping out antibodies.

Killer T cells recognise antigens presented on which MHC molecules, and carry which co-receptor?

Helper T cells, by contrast, read Class II MHC with their CD4 co-receptor.

Killer T cells release which pore-forming cytotoxin to punch holes in a target cell's membrane?

Granulysin then enters and induces the target cell to undergo apoptosis.

Roughly how many MHC:antigen complexes must bind a helper T cell to activate it, compared with a single one for a killer T cell?

Helper cells also need longer engagement with an antigen-presenting cell.

What is the shape of a single antibody molecule?

Its variable tips bind antigen; the tail, or Fc region, is far less variable.

Human antibodies come in how many classes, or isotypes?

IgA, IgD, IgE, IgG and IgM; IgG and IgA are further split into subclasses.

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

Babies are born with 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?

It is normally the least abundant isotype and evolved to fight parasitic worms.

The study of antibodies began in 1890 when Emil von Behring and which Japanese bacteriologist described serum activity against diphtheria and tetanus toxins?

They proposed the theory of humoral immunity.

Antigens were originally so named because they are what?

They are non-self molecules that bind specific immune receptors and provoke a response.

Natural killer cells recognise and destroy compromised host cells by detecting what condition?

Cells with low levels of MHC I, as in some viral infections, lose the brakes that killer-cell immunoglobulin receptors normally apply.

Natural killer cells make up roughly what share of circulating lymphocytes in humans?

They are identified as CD56-positive and CD3-negative.

What are the four classic symptoms of inflammation?

They are caused by increased blood flow, driven by eicosanoids and cytokines from injured cells.

Which class of eicosanoid produces fever and dilates blood vessels during inflammation?

Leukotrienes attract white blood cells; interleukins carry messages between them.

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

Hyperthermia, by contrast, is a rise above an unchanged set point and does not respond to antipyretics.

The complement system is a cascade of more than how many proteins that attacks foreign cell surfaces?

It is named for its ability to complement the killing of pathogens by antibodies, and ends in a membrane attack complex.

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

Complement fragments also attract immune cells and increase vascular permeability.

In 1891 Hans Buchner named the bactericidal property of blood "alexin", from a Greek word meaning what?

Jules Bordet then split it into a heat-stable sensitiser and a heat-sensitive part that Ehrlich renamed complement in 1899.

Toll-like receptors, which detect pathogen-associated molecular patterns, were first discovered in which organism?

Ten toll-like receptors have been described in humans.

Dendritic cells are named for their resemblance to what?

Found in skin, nose, lungs and gut, they present antigens to T cells, linking innate and adaptive immunity.

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

Basophils and eosinophils mainly defend against parasites and contribute to asthma.

Which organ acts as a blood filter, removes old red blood cells and holds a reserve of blood?

It also recycles iron and is built like a very large lymph node.

Kupffer cells in the liver and microglia in the brain are tissue-resident forms of which large phagocytic cell, first named in 1884?

They all belong to the mononuclear phagocyte system.

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

It is a lentivirus, a subgroup of retrovirus, and also infects macrophages and dendritic cells.

Chronic granulomatous disease is an inherited immunodeficiency in which which cells have a reduced ability to destroy pathogens?

Severe combined immunodeficiency, another genetic disorder, disrupts the development of functional T and B cells.

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

In rich countries obesity, alcoholism and drug use are common causes; immune responses also decline from about age 50.

Which of these is a common autoimmune disease?

Rheumatoid arthritis, type 1 diabetes and lupus are others; autoimmunity is the immune system attacking self.

Hypersensitivity reactions are divided into how many types?

Type I is immediate and IgE-mediated; Type IV is delayed and T-cell-mediated, taking two to three days.

Which sex hormone is described as immunosuppressive, while female sex hormones stimulate immune responses?

Autoimmune diseases such as lupus strike women preferentially, often from puberty.

Edward Jenner tested his hypothesis in 1796 by inoculating which eight-year-old boy, the son of his gardener?

He used pus from milkmaid Sarah Nelmes, who had caught the disease from a cow named Blossom.

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

Louis Pasteur proposed in 1881 that the term be extended to all protective inoculations, in Jenner's honour.

Which two diseases have so far been eradicated worldwide through vaccination and herd immunity?

Rinderpest was a cattle disease; polio and measles have been eliminated only from parts of the world.

Which 10th-century Persian physician wrote the first recorded theory of acquired immunity, noting smallpox survivors did not catch it again?

He explained it as excess moisture being expelled from the blood.

Interferons, named for interfering with viral replication, were first described in 1957 by which pair in London?

They were studying viral interference at the National Institute for Medical Research.

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

His observation about the Plague of Athens is one of the earliest descriptions of acquired immunity.

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

Skin and airways also secrete antimicrobial peptides called defensins, and stomach acid kills swallowed microbes.

When B or T cells meet their matching antigen and multiply into many identical copies, the process is called what?

Each B cell lineage carries a different antibody, so together they represent every antibody the body can make.

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

It lasts from a few days to several months because the infant makes no memory cells of its own.

Which element does Wikipedia's article say is necessary for the development and activity of the organ where T cells mature?

Double-positive T cells are exposed there to a wide range of self-antigens so that self-reactive ones can be eliminated.

The MHC gets its name from its discovery during the study of what?

George Snell identified an MHC locus by breeding mouse strains that differed only in histocompatibility.

Which glucocorticoid side effects does the article list as reasons their use is tightly controlled?

They are the most powerful anti-inflammatory drugs; cyclosporin instead blocks T-cell signalling.

Which enzyme, expressed at high levels, turns melanocytes into melanoma tumours that the immune system may recognise as foreign?

Immune surveillance targets tumour antigens, some from viruses such as HPV.