Immune System Questions and Answers

Answer: C

Correct answer: Memory cells

What makes active immunity last is the pool of memory cells left behind after a response. They persist for years and, on meeting the same antigen again, produce a response that is faster, larger and of higher affinity - the basis of vaccination. Killer, helper and suppressor T cells all act during a response but do not carry its memory.

Answer: B

Correct answer: Resistance developed after disease

Active immunity is what the body builds by responding to an antigen - after an infection, or after a vaccine. It takes days or weeks to develop, but it leaves memory cells and so lasts. Resistance present before any encounter would be innate immunity.

Answer: A

Correct answer: RNA virus

HIV is a retrovirus: its genome is RNA, which reverse transcriptase copies into DNA that is then integrated into the host chromosome. It infects CD4 helper T cells, and their gradual loss is what leaves the patient open to the opportunistic infections that define AIDS.

Answer: C

Correct answer: Ig G

IgG makes up roughly 75-80% of the immunoglobulin in serum. It dominates the secondary response, activates complement, opsonises for phagocytosis, and is the only class that crosses the placenta - which is what protects a newborn for its first few months.

Answer: C

Correct answer: Neutrophils

Neutrophils are innate: they are the first phagocytes to reach an infection, and they recognise general microbial patterns rather than a specific antigen. T and B lymphocytes belong to the acquired response, and thyroid cells have no immune role.

Answer: B

Correct answer: Histamine and kinins

The swelling and redness round a bite are produced by locally released mediators. Histamine comes from mast cell granules and dilates the small vessels while making them leaky; kinins, chiefly bradykinin, do the same and also stimulate the pain fibres, which is why the spot itches and hurts. Interferons act against viruses, opsonins tag microbes for phagocytosis, and histones are nuclear proteins.

Answer: D

Correct answer: Isoimmunised

The Rh-negative recipient has no D antigen, so the transfused Rh-positive cells are foreign and provoke an immune response - the recipient becomes isoimmunised, that is, sensitised, and now carries anti-D antibodies. The first transfusion often passes without a dramatic reaction; the danger is the next exposure, and, in a woman, a later Rh-positive pregnancy.

Answer: A

Correct answer: Rh- Rh-, Rh+ Rh-

Rh-negative is recessive, so the woman must be homozygous recessive. The man is Rh-positive, and since only one of the three children was affected he evidently passed the negative allele to the others - so he is heterozygous. Each child then has a one in two chance of being Rh-positive and so at risk.

Answer: A

Correct answer: Glycoproteins

An antibody is a protein with carbohydrate chains attached - a glycoprotein. Its four polypeptide chains, two heavy and two light, are held by disulphide bonds into the familiar Y, with the sugars on the constant region of the heavy chains, where they help determine how the antibody is handled once bound.

Answer: C

Correct answer: Brain

The brain is not a lymphoid organ; indeed it is immunologically privileged, shielded by the blood-brain barrier and patrolled by its own resident microglia rather than by circulating lymphocytes. The thymus is where T cells mature, and the spleen and lymph nodes are where antigen and lymphocytes are brought together for a response to begin.