A molecule that produces an immune response is
Answer: A
Correct answer: Antigen
An antigen is any molecule the immune system recognises as foreign and responds to - typically a protein or polysaccharide on a microbe’s surface. An antibody is the response, not the trigger; carcinogens cause cancer and mutagens damage DNA.
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A noninfectious unnatural and unusual reaction to asubstance or condition is
Answer: B
Correct answer: Allergy
An allergy is an exaggerated immune response to something harmless - pollen, a food, a drug. It is not an infection, since no pathogen is involved, and the damage is done by the reaction rather than by the substance itself.
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Which of the following kinds of immunity is present from birth?
Answer: A
Correct answer: Innate Immunity
Innate immunity is present from birth and needs no prior exposure: skin and mucous membranes, gastric acid, phagocytes, natural killer cells, complement and interferons. It responds within minutes to hours, but always in the same way, with no memory. Acquired immunity, active or passive, is built up afterwards.
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Passive immunity is obtained through injecting
Answer: C
Correct answer: Antibodies
Passive immunity is conferred by injecting ready-made antibodies - antiserum or immunoglobulin, as after a snake bite or a possible tetanus exposure. Protection begins at once but fades in weeks. A vaccine does the opposite: it supplies antigen and makes the body produce its own response.
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Which of the following engulfs foreign material?
Answer: A
Correct answer: Macrophages
Macrophages are the principal phagocytes of the tissues: they engulf microbes and debris and digest them. Plasma cells secrete antibody, mast cells release inflammatory mediators, and lymphocytes act through receptors and antibodies rather than by eating.
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In a fetus, where are lymphocytes produced?
Answer: C
Correct answer: In the liver
Haematopoiesis moves about during development: it begins in the yolk sac, and through most of gestation the fetal liver is the main site, with the spleen contributing. Only towards the end does the bone marrow take over, and it remains the site for life.
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The protein, produced by B cells that binds to a specific antigen is
Answer: D
Correct answer: antibody
An antibody (immunoglobulin) is the Y-shaped protein secreted by plasma cells, with two binding sites shaped to fit one particular antigen. Binding neutralises the antigen, marks it for phagocytosis, or triggers complement. A phagocyte and a leucocyte are cells; a vaccine is a preparation that provokes antibody rather than being one.
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Antibodies are formed by
Answer: D
Correct answer: B-cells
B cells make antibody - each with the same specificity as the receptor that first bound the antigen. On activation they divide and mature into plasma cells, which do the actual secreting. T cells direct the response but secrete no antibody; monocytes and phagocytes engulf.
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How many types of antibodies are there?
Answer: A
Correct answer: Five
There are five classes of antibody, distinguished by their heavy chains: IgG, the commonest, and the only one crossing the placenta; IgM, a pentamer made first in a new response; IgA, which guards mucosal surfaces and appears in milk; IgE, involved in allergy and in defence against parasites; and IgD, a receptor on naive B cells.
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The maturation of T cells and the production of particular T cell receptors occurs in the
Answer: B
Correct answer: thymus gland
T cells are made in the bone marrow but mature in the thymus - which is what the T stands for. There they rearrange their receptor genes and are then screened twice: cells whose receptor cannot recognise self MHC die, and cells that react too strongly to the body’s own antigens are deleted. Only about 2% survive both tests.
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