## **Core Concept**
The human immunodeficiency virus (HIV) primarily targets and infects a specific subset of lymphocytes, leading to a compromised immune system. The infection process involves the virus binding to specific receptors on the surface of these cells. Understanding the primary target cells of HIV is crucial for managing and treating the infection.

## **Why the Correct Answer is Right**
HIV most commonly infects **CD4+ T lymphocytes**, also known as T helper cells. These cells play a pivotal role in the immune response by assisting in the activation and direction of other immune cells. The virus enters these cells by binding to the CD4 receptor and a co-receptor, typically CCR5 or CXCR4, on the surface of the CD4+ T cells. This binding allows the virus to fuse with the cell membrane and release its genetic material into the cell, initiating the infection process.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While B cells are crucial for antibody production and immune response, they are not the primary target cells for HIV infection.
- **Option B:** Similarly, cytotoxic T cells (CD8+ T cells) are vital for killing infected cells and tumor cells but are not the main target for HIV.
- **Option D:** Neutrophils are a type of white blood cell important in the innate immune response, particularly in fighting bacterial infections, but they are not primarily targeted by HIV.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the depletion of CD4+ T cells is a hallmark of HIV infection progression, leading to immunodeficiency. The level of CD4+ T cells is used as a critical marker for assessing the stage of HIV infection and guiding treatment decisions.

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