Atopic people produce an increased amount of IgE. Of the following, which is the most likely explanation for the increased amount of IgE?

Correct Answer: D

Rationale: IL-4 from Th2 cells drives B cells to produce IgE, a key factor in atopy and allergic responses.

Correct Answer: A

Rationale: DiGeorge syndrome is caused by a 22q11.2 deletion (often written as 22q12 in shorthand), affecting thymic development. No other listed condition matches this chromosomal defect.

Correct Answer: D

Rationale: The NBT test is a specific diagnostic test for CGD, not part of initial screening. CBC, lymphocyte count, and immunoglobulin levels are broad screening tools for immunodeficiency.

Correct Answer: C

Rationale: CGD is caused by an inability to activate the neutrophil respiratory burst, impairing oxidative killing of ingested microbes.

Correct Answer: C

Rationale: T-cell defects lead to impaired cellular immunity, increasing susceptibility to opportunistic infections like fungi and Pneumocystis jiroveci.