**Core Concept**
HIV encephalitis is a complication of HIV infection, characterized by inflammation and damage to the brain tissue. The histopathological features of HIV encephalitis are crucial for diagnosing this condition.

**Why the Correct Answer is Right**
The correct answer is **Multinucleated giant cell**. This is because multinucleated giant cells are a hallmark of HIV encephalitis, resulting from the fusion of infected cells. They are formed when the HIV virus infects and fuses the cell membranes of two or more macrophages or microglial cells, creating a large cell with multiple nuclei. This phenomenon is due to the expression of the HIV envelope glycoprotein gp120, which causes the fusion of cells.

**Why Each Wrong Option is Incorrect**
* **Option A:** Negri body is a histopathological feature of rabies, not HIV encephalitis.
* **Option B:** Lewy body is associated with Parkinson's disease and other neurodegenerative disorders, not HIV encephalitis.
* **Option C:** Fibrillary plaques are characteristic of Alzheimer's disease, not HIV encephalitis.
* **Option D:** Microglial nodules can be seen in other conditions, such as neurosyphilis, but are not specific to HIV encephalitis.

**Clinical Pearl / High-Yield Fact**
Multinucleated giant cells are a key feature of HIV encephalitis, and their presence can aid in the diagnosis of this condition.

**Correct Answer:** . Multinucleated giant cell