**Core Concept**
HIV encephalitis is characterized by the infiltration of HIV-infected macrophages and microglial cells into the brain, leading to a chronic inflammatory response and neuronal damage. This process results in distinctive histopathological changes that are diagnostic of the condition.

**Why the Correct Answer is Right**
The histopathological features of HIV encephalitis include the presence of multinucleated giant cells, which are formed by the fusion of infected macrophages and microglial cells. These cells are typically found in the cerebral cortex and white matter, and are accompanied by a chronic inflammatory response characterized by the presence of lymphocytes and macrophages. The underlying mechanism involves the entry of HIV into macrophages and microglial cells via the CD4 receptor, leading to viral replication and cell damage.

**Why Each Wrong Option is Incorrect**
**Option A:** Astrocyte proliferation and gliosis are features of various neurodegenerative conditions, but are not specific to HIV encephalitis.
**Option B:** Neutrophil infiltration is not a characteristic feature of HIV encephalitis, which is primarily associated with a chronic inflammatory response involving lymphocytes and macrophages.
**Option C:** Vasculitis is not a hallmark of HIV encephalitis, which is primarily characterized by the infiltration of HIV-infected macrophages and microglial cells into the brain parenchyma.

**Clinical Pearl / High-Yield Fact**
HIV encephalitis is a key differential diagnosis in patients with HIV infection and neurological symptoms, particularly those with cognitive impairment and dementia. The presence of multinucleated giant cells on histopathological examination is a diagnostic clue to this condition.

**Correct Answer: A. Multinucleated giant cells are a characteristic histopathological feature of HIV encephalitis.**