Question 1

What is the cause of photo contact dermatitis?

Accepted Answer

Drugs or drug metabolites act as haptens and bind to MHC class II molecules on Langerhans cells. Exposure to sunlight induces structural changes in the complex of drug/MHC class I molecule, which creates an antigen that is recognized by CD4 Th1 cells. The CD4 cells release cytokines that induce skin changes.

Question 2

Patients with celiac sprue need to avoid what agent?

Accepted Answer

Patients with celiac sprue have delayed-type hypersensitivity (DTH) reactions to gluten, a component of wheat, rye, barley, and oats. The DTH response damages the cells that line the gastrointestinal tract, adversely affecting the absorption of foods. Patients may experience diarrhea and even a failure to thrive due to malnutrition. Therefore, patients with celiac sprue must avoid foods that contain gluten.

Question 3

Why are Mycobacterium avium complex (MAC) infections more difficult to treat?

Accepted Answer

MAC organisms are resistant to many antibiotics, so there are not many treatment options.

Question 4

What is an advantage of in vitro testing over the PPD skin test for TB? 
I. The test is more accurate
II. The test can be completed in 1 day
III. The test is not affected by prior TB vaccinations

Accepted Answer

All of these are True regarding the in vitro testing option for TB. The test is more accurate than the skin test because there is no reader, which means there is no potential for bias or confusion in interpretation. The test can be completed in 1 day and does not require the patient to come back a second time for a reading. Finally, the test detects antigens that are not present in the vaccine.

Question 5

Which of the following can be found inside a granuloma?

Accepted Answer

Macrophages, lymphocytes, and fibroblasts are encapsulated with the infectious material in a final attempt to contain the infection.

Question 6

Which of the following is/are considered a genetic factor that increases susceptibility to mycobacterial infections? 
I. Defect in TNF-a receptor
II. Defect in vitamin D receptor
III. Defect in interferon-g receptor

Accepted Answer

Increased susceptibility to TB infection has been associated with defects in the vitamin D receptor and the interferon-ã receptor. TNF-a causes a significant amount of lung damage in TB, so there is no defect in that receptor.

Question 7

Defects in NRAMPs cause:

Accepted Answer

NRAMP1 reduces the pH of the phagosome, which is a key part of bacterial killing. NRAMP2 is an efflux pump that transports iron and other cations out of the phagosome. Defects in these two components lead to ineffective killing in the phagosome, and the bacteria can escape and establish infection inside the macrophage.

Question 8

What is the difference between granulomas found in coccidioidomycosis and TB?

Accepted Answer

The only difference in granulomas found in coccidioidomycosis patients is that they contain B cells in addition to the other immune cells normally found in granulomas of TB patients.

Question 9

Which of the following is present in bat droppings, putting cavers at risk for this disease?

Accepted Answer

H. capsulatum is found in bat and bird droppings, putting anyone who comes into contact with the disturbed droppings at risk for histoplasmosis, including cavers, farmers, landscapers, and construction workers. Immunocompromised patients are also at risk for acquiring histoplasmosis.

Question 10

What is the difference between a reaction to poison ivy and other delayed-type hypersensitivity reactions?

Accepted Answer

Whereas other delayed-type hypersensitivity reactions involve several immune cell types, the reaction to poison ivy only involves activation of CD8 T cells. The CD8 T cells kill any host cell that has urushiol on the cell surface.

Question 11

Why is a positive PPD skin test not sufficient to determine if a patient has active TB?

Accepted Answer

There are several scenarios in which a patient could have a positive PPD skin test but may not have active TB. The skin test indicates previous exposure, but that exposure could be due to a patient receiving a vaccine, having the latent form, or previously having active TB but not currently having active disease.

Question 12

Which of the following is a virulence factor and drug target for Mycobacterium tuberculosis?

Accepted Answer

Mycolic acids are virulence factors that are structural cell wall components. These cell wall components prevent drugs and other chemicals from entering the bacterium and causing damage.

Question 13

The main organ target for Coccidioides immitis is:

Accepted Answer

Coccidioidomycosis is spread through inhalation of contaminated soil particles, and the organisms settle in the lungs.

Question 14

What role does lipoarabinomannan play in the immune response triggered by tuberculosis (TB) infection?

Accepted Answer

Lipoarabinomannan is a virulence factor that stimulates production of TNF-a, which causes most of the lung damage by Mycobacterium.

Question 15

In which stage of TB infection does lung necrosis caused by macrophage-derived reactive oxygen species (ROS) begin?

Accepted Answer

The third phase of the disease is when lung necrosis begins. ROS derived from macrophages are released and cause necrosis of lung tissue.

Quiz 19: Delayed Type Hypersensitivity Reactions