Cough Case 2

A 70-year-old man is seen by his family practice physician during a routine office visit. The man complains of not feeling well for the last three months. Further questioning reveals that the patient has a chronic, unproductive cough that he attributes to an old smoking history. Physical
examination is notable for a 15-pound weight loss since the last office visit three months previously. A multinodular infiltrate is seen in the lung field behind and above the right clavicle.

Q 1

The patient is injected intradermally with PPD. 3 days after the injection, there is a 13-mm diameter area of induration at the injection site. This reaction is an example of which of the following types of immune response?
/ A. Type l hypersensitivity
/ B. Type ll hypersensitivity, cytotoxic subtype
/ C. Type ll hypersensitivity, noncytotoxic subtype
/ D. Type lll hypersensitivity
/ E. Type IV hypersensitivity

Q 2
Which of the following principally mediates this form of hypersensitivity?
/ A. Cytotoxic T cells, TH1 cells, and macrophages
/ B. IgE, basophils, and mast cells
/ C. IgG and complement
/ D. IgG, IgM, neutrophils, and macrophages
/ E. IgG, IgM, neutrophils, macrophages, and natural killer cells

Q 3
The strongest definitive identification of the pathogen responsible for this patient's disease would be provided by a positive result on which of the following biochemical tests?
/ A. Arylsulfatase
/ B. Heat-stable catalase
/ C. Niacin
/ D. Nitrate reductase
/ E. Urease

Q 4
The mass lesion in the patient's lung is evaluated with fiberoptic bronchoscopy with transbronchial biopsy. Sputum collected after the procedure demonstrates acid-fast bacteria with a "beaded" appearance. Giant cells found in the biopsy material would be likely to express
which of the following membrane markers?
/ A. CD4
/ B. CD8
/ C. CD14
/ D. CD16
/ E. CD19

Q 5

The principal drug recommended for treatment of this patient's disease targets which of the following molecules?
/ A. Arabinogalactan
/ B. Dihydrofolate reductase
/ C. Dihydropteroate synthetase
/ D. Mycolic acid
/ E. Peptidoglycan

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Cough Case 2 answers


A1

The correct answer is E. This patient has a positive PPD test, as indicated by an area of induration greater than or equal to 10 mm. PPD is a purified protein derivative of tuberculin, so this finding indicates that the patient has tuberculosis. The PPD reaction is an example of type IV hypersensitivity, also known as delayed-type hypersensitivity.
Type I hypersensitivity (choice A) is immediate hypersensitivity, and can be seen for example, in hay fever and atopic dermatitis.
Cytotoxic type II hypersensitivity (choice B) can be seen in autoimmune hemolytic anemia and transfusion reactions.
Noncytotoxic type II hypersensitivity (choice C) can be seen in myasthenia gravis and Graves disease.
Type III hypersensitivity (choice D) is due to immune complex deposition, and can be seen in systemic lupus erythematosus and rheumatoid arthritis.

A2

The correct answer is A. Cytotoxic T lymphocytes, T helper 1 lymphocytes, and macrophages mediate the delayed-type hypersensitivity reaction, which develops in response to viral, fungal, and intracellular bacterial antigens. Antibodies do not play a significant role in this type of response.
IgE, basophils, and mast cells (choice B) are involved in the production of type I hypersensitivity.
IgG and complement (choice C) is a mechanism of toxicity in type II cytotoxic hypersensitivity.
IgG, IgM, neutrophils, and macrophages (choice D) may be involved in types II or III hypersensitivities.
IgG, IgM, neutrophils, macrophages, and natural killers (choice E) may be involved in types II or III hypersensitivities.


A3

The correct answer is C. Mycobacterium tuberculosis is the only member of the genus Mycobacterium that is a producer of niacin.
Mycobacterium fortuitum and M. chelonae produce arylsulfatase (choice A), but M. tuberculosis does not.
Heat-stable catalase (choice B) is produced by Mycobacterium kansasii, M. avium intracellulare, and M. fortuitum, but not by M. tuberculosis.
Mycobacterium tuberculosis, M. kansasii, and M. fortuitum produce nitrate reductase (choice D), however niacin is more definitive for the identification of M. tuberculosis.

A4

The correct answer is C. CD14, the endotoxin receptor, is a standard marker for macrophages and cells of their lineage. The giant cells in a TB granuloma are histiocytes, which are modified macrophages, so they would bear macrophage cell markers.
CD4 (choice A) is a cell marker for helper T lymphocytes that would be found in the halo of lymphocytes surrounding the Langerhans giant cells, but would not be on the giant cells themselves.
CD8 (choice B) is a cell marker for cytotoxic T lymphocytes that would be present in the halo of lymphocytes surrounding the giant cells, but would not be on the giant cells themselves.
CD16 (choice D) is a cell marker for NK cells, which would not be on the giant cells in a TB granuloma.
CD19 (choice E) is a cell marker for B-lymphocytes, which are not likely to be present in a TB granuloma, a reaction mediated exclusively by cell-mediated immunity.

A5

The correct answer is D. The mainstay of therapy for tuberculosis is treatment with drugs such as isoniazid, rifampin, ethambutol, ethionamide, pyrazinamide, and streptomycin. Both isoniazid and ethionamide target the mycolic acid molecules in the mycobacterial cell wall. A single drug, usually isoniazid, can be used for chemoprophylaxis and when clinical disease is absent. Multiple drugs are usually used in other settings. Mycobacterium tuberculosis resistant to all first-line drugs is being seen with increasing frequency among AIDS patients.
Arabinogalactan (choice A) is the molecule targeted by ethambutol, which is a drug added to the anti-mycobacterial regimen only when drug-resistant strains are implicated.
Dihydrofolate reductase (choice B) is the molecule targeted by trimethoprim, which is not the principal drug recommended for treatment of tuberculosis.
Dihydropteroate synthetase (choice C) is the molecule targeted by dapsone, which is the drug of choice for Mycobacterium leprae, not M. tuberculosis.
Peptidoglycan (choice E) is the molecule targeted by the penicillins, vancomycin, and cycloserine.