## Core Concept
Whipple's disease is a rare, systemic bacterial infection caused by *Tropheryma whipplei*, primarily affecting the small intestine. The disease is characterized by malabsorption, weight loss, diarrhea, and abdominal pain. Histopathological examination is crucial for diagnosis.

## Why the Correct Answer is Right
The correct answer can be deduced by understanding the typical histopathological features of Whipple's disease. Key findings include:
- **PAS-positive macrophages**: The presence of Periodic Acid-Schiff (PAS)-positive material within macrophages is a hallmark. This material represents the glycoproteins and carbohydrates from the bacterial cell wall.
- **Villus atrophy and crypt hyperplasia**: Similar to celiac disease, Whipple's disease causes damage to the intestinal mucosa, leading to villus atrophy and crypt hyperplasia.
- **Infiltration of lamina propria by macrophages and lymphocytes**: The immune response to *T. whipplei* results in the accumulation of these cells.

## Why Each Wrong Option is Incorrect
To determine the correct answer, we need to evaluate each option based on known histopathological features of Whipple's disease.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that while the histopathological findings are critical for diagnosis, the disease can be confirmed by PCR for *T. whipplei* DNA in tissue samples or blood.

## Correct Answer: D.