## **Core Concept**
The human immunodeficiency virus (HIV) targets and gradually destroys a specific subset of lymphocytes, leading to a compromised immune system. This process involves the depletion of **CD4+ T cells**, which are crucial for immune response coordination and regulation. The impairment of the immune system results in increased susceptibility to opportunistic infections and certain types of cancers.

## **Why the Correct Answer is Right**
The correct answer, **CD4+ T cells**, is accurate because HIV specifically targets these cells through the **CD4 receptor** and **CCR5 or CXCR4 co-receptors** on their surface. Once inside the CD4+ T cells, HIV integrates its genetic material into the host cell's DNA, leading to the production of more viral particles and ultimately causing the destruction of these cells. This depletion of CD4+ T cells disrupts the immune system's ability to fight off infections and diseases.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While B cells are important for the immune response, particularly in producing antibodies, HIV's primary mechanism of immune system impairment is not through the direct destruction of B cells but through the depletion of CD4+ T cells.
- **Option B:** Similarly, neutrophils play a critical role in the innate immune response, especially against bacterial and fungal infections. However, HIV does not primarily target neutrophils.
- **Option C:** This option might seem plausible because macrophages, like CD4+ T cells, express CD4 receptors. However, the overall effect of HIV on the immune system is more directly related to the depletion of CD4+ T cells.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the progression of HIV infection can be monitored by tracking the **CD4+ T cell count**. A decrease in this count indicates a worsening of the disease and an increased risk of opportunistic infections. Conversely, antiretroviral therapy (ART) aims to suppress viral replication, thereby preserving CD4+ T cell counts and preventing disease progression.

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