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Chapter 3. Immunity, Infection, & Inflammation

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In an experiment, a scientist treats a group of mice with an antiserum that substantially depletes the number of circulating neutrophils. Compared with untreated control animals, the mice with reduced numbers of neutrophils were found to be significantly more susceptible to death induced by bacterial inoculation. The increased mortality can be ascribed to a relative deficit in which of the following?

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A. Acquired immunity

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B. Oxidants

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C. Platelets

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D. Granulocyte/macrophage colony stimulating factor (GM-CSF)

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E. Integrins

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The correct answer is B. Neutrophils are a critical source of oxidants, innate immune mediators that are involved in bacterial killing. While oxidants are also produced by macrophages, neutrophils are the primary source, making B the best answer. Acquired or adaptive immunity is mediated by lymphocytes, which should be unaffected by an experimental approach that targets neutrophils (excluding option A). Direct depletion of neutrophils also would not be expected to alter platelet numbers, and if anything would increase rather than decrease GM-CSF in an attempt to restore the neutrophil population (rules out options C and D, respectively). Finally, while integrins are involved in neutrophil diapedesis into tissues after infection, their expression also should not be reduced by a reduction in neutrophil numbers (excludes option E).

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A 20-year-old college student comes to the student health center in April complaining of runny nose and congestion, itchy eyes, and wheezing. She reports that similar symptoms have occurred at the same time each year, and that she obtains some relief from over-the-counter antihistamine drugs, although they make her too drowsy to study. Her symptoms can most likely be attributed to inappropriate synthesis of which of the following antibodies specific for tree pollen?

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A. IgA

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B. IgD

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C. IgE

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D. IgG

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E. IgM

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The correct answer is C. The symptoms described are typical for a seasonal allergy experienced when trees are in bloom. Allergic responses occur when allergens bind to and cross-link specific IgE molecules bound to the surface of mast cells located in mucosal sites, resulting in the release of histamine and other mediators. Mast cells do not express receptors for IgA, IgD, or IgM (rules out options A, B, and E). While there is some evidence that a specific subset of IgG molecules (IgG4) can contribute to allergic reactions, allergies are almost always attributable to synthesis of IgE specific for a substance that healthy subjects would find ...

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