Immune System Questions and Answers

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.

Answer: B

Correct answer: B cells

Antibodies are made by B cells - strictly, by the plasma cells they mature into - and each antibody fits one particular antigen, which is what makes the defence specific. Complement and inflammation are innate and non-specific; T cells are specific too, but they act on infected cells rather than by secreting antibody.

Answer: A

Correct answer: Lymphocytes

Lymphocytes - B and T cells - carry the specific (acquired) defence: each bears a receptor for one antigen, and the survivors of a response persist as memory. Macrophages, phagocytes and the leucocytes generally act non-specifically, engulfing whatever is marked as foreign.

Answer: D

Correct answer: repairing damage to the body wall

A clot plugs the breach: it stops the loss of blood and, just as importantly for defence, seals the wound against microbes while the tissue underneath is repaired. It is a physical barrier rather than an immune recognition mechanism - though the mesh of fibrin also traps bacteria within it.

Answer: D

Correct answer: tolerance

Tolerance is the trained unresponsiveness of the immune system to the body’s own molecules. It is established chiefly in the thymus and bone marrow, where lymphocytes reacting strongly to self antigens are deleted or silenced, and maintained afterwards by regulatory T cells. When it fails, the result is autoimmunity.

Answer: C

Correct answer: The inflammatory response

Inflammation is immediate - damaged tissue and resident macrophages release mediators within minutes, dilating vessels and drawing in phagocytes. Complement follows quickly, but the lymphocyte responses take days, because the few cells that recognise the antigen must first be found and made to divide.

Answer: A

Correct answer: Macrophages

Macrophages are the body’s scavengers: they engulf microbes, dead cells and debris, digest them in lysosomes, and then display fragments of what they have eaten to T cells. B and T cells are lymphocytes and do not phagocytose.

Answer: B

Correct answer: Cytotoxic T cell

A cytotoxic T cell recognises viral peptides displayed on the infected cell’s MHC class I molecules and kills it - by perforin and granzymes, or by triggering apoptosis - before the virus inside can finish replicating. Suppressor (regulatory) T cells damp responses down instead; exotoxins and endotoxins are bacterial poisons, not cells.

Answer: D

Correct answer: Bee sting

Injected allergen is the danger. Venom entering the bloodstream directly can trigger mast cell degranulation throughout the body within minutes, causing the collapse in blood pressure and the airway swelling of anaphylaxis. Pollen, mould and dust are inhaled, and typically cause a local reaction - rhinitis or asthma - rather than a systemic one.

Answer: A

Correct answer: active immunity

Immunity following an infection is active and naturally acquired: the body met the antigen, mounted its own response, and kept memory cells. Passive immunity is antibody received ready-made; innate immunity is present from birth and is not acquired at all.