**Core Concept**
HIV (Human Immunodeficiency Virus) is a lentivirus that targets and destroys CD4+ T lymphocytes, leading to a compromised immune system and increased susceptibility to opportunistic infections and cancers. This viral infection is characterized by its ability to integrate into the host genome and replicate using the host cell's machinery.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of HIV replication and its interaction with the host immune system. HIV infects and kills CD4+ T cells, which are crucial for the immune response. The virus uses the enzyme reverse transcriptase to convert its single-stranded RNA genome into double-stranded DNA, which is then integrated into the host genome. This integration allows the virus to hijack the host cell's machinery for replication.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because HIV does not directly kill macrophages, although it can infect them.
* **Option B:** This option is incorrect because HIV does not primarily target B cells, although it can affect their function indirectly.
* **Option C:** This option is incorrect because while HIV can cause immunosuppression, it is not primarily a gastrointestinal pathogen.

**Clinical Pearl / High-Yield Fact**
A key aspect of HIV management is initiating antiretroviral therapy (ART) early in the course of the disease to suppress viral replication and prevent further immune system damage.

**Correct Answer:** C.