48 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, making up 50-70% of leukocytes?

Neutrophils make up 50–70% of circulating leukocytes; roughly 100 billion are produced each day and they live only about 5 to 135 hours.

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

Phagocytosis traps the engulfed pathogen in a phagosome that fuses with a lysosome; it is probably the oldest form of host defence, present even in amoebae.

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

Élie Metchnikoff, working in a private lab in Messina, Sicily, watched mobile cells surround the thorns in starfish larvae; he is called the father of innate immunity.

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

T stands for thymus-derived: immature T cells migrate to the thymus, where they undergo positive and negative selection 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?

Thymic involution begins after puberty, when the gland is at its largest; over the following decades functional tissue is replaced by fat and output of new T cells falls.

Lymphocytes derive from haematopoietic stem cells in which tissue?

Bone marrow houses the haematopoietic stem cells that give rise to all lymphocytes; human marrow turns out about 500 billion blood cells a day.

B cells are responsible for which arm of adaptive immunity?

B cells drive the humoral response: activated B cells become plasma cells pumping antibodies into body fluids, while T cells handle cell-mediated immunity.

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

Cytotoxic T cells carry the CD8 co-receptor and read peptides on MHC I, which almost all nucleated cells display; helper T cells read class II with CD4.

Killer T cells release which pore-forming cytotoxin to punch holes in 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.

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?

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.

Human antibodies come in how many classes, or isotypes?

There are five classes: 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?

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 mediates the immediate Type I 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?

Kitasato Shibasaburō and von Behring showed in 1890 that serum from immunised animals neutralised diphtheria and tetanus toxins, founding 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?

The 'missing self' hypothesis: cells with low MHC I, as in some viral infections or tumours, lose the brakes that killer-cell immunoglobulin-like receptors normally apply, so NK cells attack.

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

NK cells make up roughly 5-20% of circulating lymphocytes in humans and are identified as CD56-positive and CD3-negative.

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.

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

Prostaglandins such as PGE2 cause fever and dilate blood vessels, which is why aspirin, a prostaglandin blocker, lowers both; leukotrienes attract white blood cells instead.

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.

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

More than 20 plasma proteins make up the cascade, named for its ability to complement the killing of pathogens by antibodies; it ends in a membrane attack complex.

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

Opsonisation coats the pathogen with C3b or antibody so engulfing cells bind and swallow it more readily; 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?

Alexin comes from the Greek alexein, 'to ward off'; Jules Bordet then split it into a heat-stable sensitiser and a heat-labile part that Ehrlich renamed complement in 1899.

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

The Toll gene was found in Drosophila fruit flies, where Jules Hoffmann's lab showed in 1996 that it drives antifungal defence; ten toll-like receptors have since been described in humans.

Dendritic cells are named for their resemblance to what?

Dendritic cells are named for their resemblance to the branches of neurons, the dendrites; 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?

Mast cells sit in connective tissue and mucous membranes and release histamine when IgE on their surface is cross-linked, driving allergy and anaphylaxis; basophils and eosinophils mainly target parasites.

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

The spleen filters blood, removes worn-out red cells, recycles their iron and holds a reserve of blood; structurally it is built like a very large lymph node.

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

Kupffer cells and microglia are tissue-resident macrophages, a cell type Metchnikoff named in 1884; they all belong to the mononuclear phagocyte system.

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

HIV binds CD4 and infects CD4+ helper T lymphocytes; a count below 200 cells per microlitre defines AIDS. The lentivirus also infects macrophages and dendritic cells.

In chronic granulomatous disease, an inherited immunodeficiency, which cells have a reduced ability to destroy pathogens?

In chronic granulomatous disease phagocytes lack a working NADPH oxidase, so they engulf microbes but cannot produce the oxidative burst that kills them.

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

Malnutrition, especially protein-energy deficiency, is the leading cause of immunodeficiency in developing countries; in rich countries obesity, alcoholism and drug use are common causes, and responses decline from about age 50.

Which of these is a common autoimmune disease?

Hashimoto's thyroiditis, in which antibodies attack the thyroid, is one of the most common autoimmune diseases; rheumatoid arthritis, type 1 diabetes and lupus are others.

Hypersensitivity reactions are divided into how many types?

The Gell and Coombs scheme has four types: Type I is immediate and IgE-mediated; Type IV is delayed and T-cell-mediated, taking two to three days.

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

James Phipps, the eight-year-old son of Jenner's gardener, was inoculated on 14 May 1796 with 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?

Variolae vaccinae, 'smallpox of the cow', was Jenner's name for cowpox; Louis Pasteur proposed in 1881 that 'vaccine' be extended to all protective inoculations in Jenner's honour.

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

Smallpox was declared eradicated in 1980 and rinderpest, a cattle plague, in 2011, both through vaccination campaigns.

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?

Alick Isaacs and Jean Lindenmann, studying viral interference at the National Institute for Medical Research in Mill Hill, reported interferon in 1957.

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

Thucydides, in his history of the Peloponnesian War, noted that survivors of the Plague of Athens in 430 BC could nurse the sick safely, one of the earliest descriptions of acquired immunity.

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

Lysozyme, discovered by Alexander Fleming in 1922, breaks down bacterial cell walls in saliva, tears and breast milk; skin and airways also secrete antimicrobial peptides called defensins.

When B or T cells meet their matching antigen and multiply into many identical copies, 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 described as what kind?

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.

Which transcription factor defines regulatory T cells?

FOXP3 is the master transcription factor of regulatory T cells; mutations in its gene cause IPEX, a severe multi-organ autoimmune syndrome in boys.

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

The major histocompatibility complex was found while studying transplanted tissue compatibility: George Snell identified its locus by breeding mouse strains that differed only in whether they rejected each other's grafts.

Which trio of side effects limits long-term glucocorticoid use?

Central obesity, hyperglycaemia and osteoporosis are classic side effects of long-term glucocorticoids, the most powerful anti-inflammatory drugs; cyclosporin instead blocks T-cell signalling.

Which melanocyte enzyme serves as a tumour antigen recognised by T cells in melanoma?

Tyrosinase, the pigment-making enzyme of melanocytes, is one of the melanoma antigens that cytotoxic T cells can recognise; immune surveillance also targets viral tumour antigens such as HPV proteins.