Immune System Questions and Answers

Answer: B

The only antibody that crosses the placenta is IgG.

IgG is actively carried across the placenta by neonatal Fc receptors on placental cells. It gives the newborn passive immunity for the first few months of life, against the infections the mother has antibodies to.

IgM is a large pentamer that cannot cross, so IgM in a newborn's blood points to an infection acquired in the womb. IgA is secreted in mucus, saliva and breast milk, especially colostrum, reaching the baby by feeding rather than across the placenta. IgD is found mainly on the surface of B cells.

Answer: A

Correct answer: Immune system

The immune system is the body’s defence against pathogens: barriers such as skin and mucus keep most out, and the cells and antibodies of the blood and lymph deal with what gets in. The digestive, excretory and respiratory systems have their own jobs - though each carries immune defences of its own, such as gastric acid and the mucus-and-cilia escalator of the airways.

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.

Answer: B

Correct answer: Cellular barriers

These are all leucocytes - white blood cells - and they make up the cellular arm of innate defence: neutrophils and monocytes engulf invaders, eosinophils attack parasites, basophils release inflammatory mediators, and lymphocytes carry the acquired response. Physical barriers are the skin and linings; physiological barriers are conditions such as acid and temperature; cytokine barriers are the interferons.

Answer: D

Correct answer: Acquired immunity

B and T lymphocytes are the cells of acquired (adaptive) immunity. Each carries a receptor for one particular antigen, so the response is specific, and the survivors of a response persist as memory cells - which is why a second exposure is dealt with faster and harder. Innate immunity uses no such receptors and has no memory.

Answer: A

Correct answer: Deficiency diseases

A poor immune system means it cannot mount an adequate response, so the disorders are immunodeficiency diseases - inherited ones such as SCID, or acquired ones such as AIDS - and their hallmark is repeated or unusual infection. Autoimmune disease is the opposite fault: an immune system that is too active and attacks the body’s own tissue.

Answer: D

Correct answer: All of the above.

All three are true of passive immunity, and they follow from one fact: the antibodies are given, not made. Protection is therefore immediate, since no response has to be mounted; it is short-lived, weeks to months, because the antibodies are gradually broken down and nothing replaces them; and it can provoke reactions, since antiserum raised in another species is itself foreign protein.

Answer: C

Correct answer: Immunology

Immunology is the study of immune systems. Botany is the study of plants, microbiology of micro-organisms, and biotechnology the use of living systems for practical ends - each may touch on immunity but none is defined by it.

Answer: A

Correct answer: T-cells

Cell-mediated immunity is carried by T lymphocytes: cytotoxic T cells kill infected or cancerous cells directly, and helper T cells direct the rest of the response. B cells work through the antibodies they secrete, which is the humoral arm.

Answer: A

Correct answer: Active immunity

Active immunity lasts because the body has made the response itself: it retains memory cells that can be roused quickly on re-exposure, so protection can last years or a lifetime. Passive immunity supplies ready-made antibodies but leaves no memory, so it fades as those antibodies are broken down.