A 31-year-old man with AIDS complains of difficulty in 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 patient's symptoms are indicative of oral and esophageal candidiasis, a fungal infection caused by *Candida albicans*. This condition arises due to an imbalance in the normal flora of the oral cavity, which is often seen in immunocompromised individuals.

**Why the Correct Answer is Right**
In individuals with AIDS, the loss of CD4+ T cells (a type of T lymphocyte) impairs the immune system's ability to regulate the normal flora of the oral cavity. As a result, *Candida albicans*, a normally commensal fungus, overgrows and forms whitish, ulcerated lesions. CD4+ T cells play a crucial role in activating macrophages and promoting cell-mediated immunity, which is essential for controlling fungal infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** Macrophages are indeed involved in the immune response to fungal infections, but their loss is not the primary cause of oral and esophageal candidiasis in AIDS patients.
* **Option B:** Neutrophils are a type of white blood cell that helps fight infections, but their loss is not directly linked to the development of oral and esophageal candidiasis in AIDS patients.
* **Option D:** B cells are a type of lymphocyte involved in the humoral immune response, but their loss is not the primary cause of oral and esophageal candidiasis in AIDS patients.

**Clinical Pearl / High-Yield Fact**
AIDS patients are prone to opportunistic infections, including oral and esophageal candidiasis, due to their compromised immune system. This highlights the importance of prompt diagnosis and treatment of fungal infections in immunocompromised individuals.

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

✓ Correct Answer: B. Helper T lymphocytes