Which of the following protects our body against disease-causing pathogens?
Answer: B
Correct answer: Immune system
The immune system is what defends against pathogens - barriers, phagocytes, complement, and the lymphocytes and antibodies of the acquired response. The respiratory, digestive and excretory systems serve gas exchange, nutrition and waste removal respectively.
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The hepatitis B vaccine is an example of _______.
Answer: D
Correct answer: Recombinant Vaccine
The hepatitis B vaccine is made by inserting the gene for the virus’s surface antigen into yeast, which then manufactures the protein - so it is a recombinant vaccine, the first to be licensed. It contains only one viral protein and no virus at all, so it cannot cause infection. (It is a subunit vaccine as well; “recombinant” is the more precise description, naming how the subunit is produced.)
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Which of the following statements is true about the IgM of humans?
Answer: D
Correct answer: IgM is primarily restricted in the circulation
Secreted IgM is a pentamer - five units joined by a J chain, and far too large to cross the capillary wall or the placenta. It therefore stays largely in the bloodstream. IgG is the one that crosses the placenta, IgA protects mucosal surfaces, and IgM is made early in a response by plasma cells before affinity maturation, so its affinity is low - a shortcoming its ten binding sites compensate for.
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Interferons are
Answer: A
Correct answer: Cytokine barriers
Interferons are cytokines released by virus-infected cells; they make neighbouring cells resistant to infection and rouse natural killer cells. They belong to the cytokine barrier of innate immunity - chemical signals rather than physical structures or cells.
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Which of the following cells of the immune system do not perform phagocytosis?
Answer: D
Correct answer: Basophil
Basophils do not phagocytose. They are the circulating counterparts of mast cells: they carry granules of histamine and heparin and release them, driving inflammation and allergic reactions. Macrophages and neutrophils are the principal phagocytes, and eosinophils will engulf antigen-antibody complexes as well as attacking parasites.
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Monocytes differentiate into which kind of phagocytic cells?
Answer: C
Correct answer: Macrophage
A monocyte circulates in the blood for a day or so, then migrates into a tissue and matures into a macrophage - a long-lived, highly phagocytic cell that also presents antigen to T cells. Tissue macrophages go by local names: Kupffer cells in the liver, microglia in the brain, alveolar macrophages in the lung.
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What is not required in the innate immune responses?
Answer: D
Correct answer: previous contact
Innate immunity acts on the first encounter, because it recognises broad patterns shared by whole classes of microbe rather than one particular antigen. No previous contact is needed - and that is precisely what distinguishes it from acquired immunity, which must be primed before it can act.
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Which of the following groups of pathogens always resides intracellularly in the host?
Answer: A
Correct answer: virus
Viruses are obligate intracellular parasites: they have no metabolism of their own and can replicate only by using a host cell’s machinery. Fungi, moulds and most bacteria grow perfectly well outside cells, though a few bacteria - Chlamydia and Rickettsia - are intracellular too.
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The phagocytes can recognize pathogens by means of _____________________
Answer: C
The pathogens make their initial contact with phagocytic cells (dendrites and macrophages) which possess pattern recognition receptors (PRRs). The PRRs can recognize the highly conserved macromolecules in bacteria and viruses.
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Which of the following proteins in the fruit fly governs the dorsoventral polarity of the fly embryo?
Answer: A
Correct answer: Toll
Toll was discovered in Drosophila as the gene setting up the embryo’s dorsoventral axis, and was later found to control the fly’s antifungal defence as well. That second role led to the discovery of the mammalian Toll-like receptors, which recognise conserved microbial patterns - work that won the 2011 Nobel Prize.
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