A 31-year-old man with AIDS complains of difficulty swallowing. Examination of his oral cavity demonstrates whitish membranes covering much of his tongue and palate. Endoscopy also reveals several whitish, ulcerated lesions in the esophagus. These pathologic findings are fundamentally caused by loss of which of the following immune cells in this patient?

**Core Concept**
The underlying condition described is **esophageal candidiasis**, an opportunistic infection that takes advantage of a compromised immune system, particularly in individuals with AIDS. This condition is characterized by the overgrowth of *Candida albicans*, a type of fungus. The immune system, specifically **cell-mediated immunity**, plays a crucial role in controlling such infections.

**Why the Correct Answer is Right**
The correct answer is related to the loss of **CD4+ T cells**, which are a type of T lymphocyte essential for cell-mediated immunity. In AIDS, the human immunodeficiency virus (HIV) targets and destroys these cells, leading to a weakened immune system that cannot effectively combat opportunistic infections like *Candida*. The depletion of CD4+ T cells impairs the body's ability to mount an adequate response against fungal pathogens, resulting in conditions such as esophageal candidiasis.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while neutrophils are important for combating infections, their loss is more closely associated with bacterial infections rather than fungal infections like candidiasis.
**Option B:** Incorrect as macrophages, although involved in the immune response, are not the primary cells responsible for defense against *Candida*.
**Option C:** Incorrect because the loss of B cells (which produce antibodies) would more significantly impact the humoral immune response rather than the cell-mediated response crucial for controlling *Candida* infections.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that esophageal candidiasis is a common complication in AIDS patients due to their compromised immune status, particularly the depletion of CD4+ T cells. Recognizing the clinical presentation, such as difficulty swallowing and whitish membranes in the oral cavity and esophagus, is crucial for prompt diagnosis and treatment.

**Correct Answer:** D. CD4+ T cells.

✓ Correct Answer: B. Helper T lymphocytes