Question 1

Which of the following best describes the sequence of events during a Type I hypersensitivity reaction upon first and subsequent exposures to an allergen, as illustrated in the provided diagram?

Accepted Answer

First exposure: Allergen binds to B cell, which differentiates into plasma cells that secrete IgE. Subsequent exposure: Allergen binds to IgE on sensitized mast cells, causing release of histamine and other mediators.

Question 2

A patient presents with the skin lesions shown in the second image. Which immune disorder is most likely responsible for these lesions, and what is the underlying cause?

Accepted Answer

Kaposi’s sarcoma associated with AIDS; caused by immunodeficiency due to destruction of TH cells.

Question 3

Which of the following best explains why antihistamines are effective in treating allergy symptoms?

Accepted Answer

They block histamine receptors on target cells, preventing pro-inflammatory effects.

Question 4

A patient with a history of severe peanut allergy experiences sudden difficulty breathing, low blood pressure, and widespread swelling after accidental exposure. What is the most appropriate immediate treatment, and why?

Accepted Answer

Administration of epinephrine to cause airway relaxation and systemic vasoconstriction.

Question 5

Which of the following mechanisms is responsible for the tissue damage seen in Type III hypersensitivity reactions?

Accepted Answer

Deposition of immune complexes in tissues, leading to inflammation and neutrophil recruitment.

Question 6

A patient receives a mismatched blood transfusion and develops hemolysis. Which type of hypersensitivity reaction is this, and what is the underlying mechanism?

Accepted Answer

Type II; antibodies bind to erythrocyte antigens, activating complement and causing cell lysis.

Question 7

Which of the following best describes the mechanism of action of antileukotriene agents in allergy treatment?

Accepted Answer

They block the enzyme that produces leukotrienes, inhibiting allergic inflammation.

Question 8

A patient develops a red, itchy rash after contact with poison ivy. Which type of hypersensitivity reaction is this, and what immune cells are primarily involved?

Accepted Answer

Type IV; T helper cells and macrophages.

Question 9

Which of the following is a primary immunodeficiency disorder characterized by failure of lymphoid cell lines and low levels of lymphocytes?

Accepted Answer

Severe combined immunodeficiency (SCID)

Question 10

Which of the following best explains why patients with AIDS are at increased risk for opportunistic infections?

Accepted Answer

Destruction of TH cells impairs both innate and adaptive immune responses.

Question 11

Which of the following is the correct LaTeX representation for the equation describing the transcription of viral RNA into DNA by reverse transcriptase?

Accepted Answer

$$	ext{RNA} \xrightarrow{	ext{reverse transcriptase}} 	ext{DNA}$$

Question 12

Which of the following scenarios best illustrates molecular mimicry leading to autoimmunity?

Accepted Answer

A viral antigen resembles a self antigen, activating T cells that attack heart muscle after a streptococcal infection.

Question 13

Which of the following best describes the purpose of allergen immunotherapy ('allergy shots')?

Accepted Answer

To induce tolerance to the allergen and diminish the IgE response.

Question 14

A patient with multiple sclerosis has T cells attacking the myelin sheath of neurons. Which mechanism most likely led to this autoimmune response?

Accepted Answer

Release of previously sequestered self antigens due to trauma or infection.

Question 15

Which of the following best explains why corticosteroids are effective in treating asthma related to allergies?

Accepted Answer

They block the synthesis of leukotrienes and prostaglandins, inhibiting allergic inflammation.

Question 16

Which of the following is a common side effect of first-generation antihistamines, and what is the physiological reason?

Accepted Answer

Drowsiness; because histamine also acts as a neurotransmitter in the brain.

Question 17

Which of the following best describes the Mantoux (PPD) test for tuberculosis exposure?

Accepted Answer

It is a delayed-type hypersensitivity reaction mediated by sensitized T cells.

Question 18

Which of the following is the most common cause of secondary immunodeficiency worldwide?

Accepted Answer

Acquired immunodeficiency syndrome (AIDS) caused by HIV-1 infection.

Question 19

Which of the following best explains the pathogenesis of type 1 diabetes mellitus as an autoimmune disorder?

Accepted Answer

Inappropriate expression of class II MHC molecules activates T cells against pancreatic beta cells.

Disorders of the Immune System: Hypersensitivity, Immunodeficiency, and Autoimmunity

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