HIV mostly affects which cells?
**Core Concept**
HIV primarily targets and infects a specific subset of immune cells, compromising the body's ability to fight off infections and diseases. This subset of cells is crucial for the immune system's function, and their depletion leads to the characteristic immunodeficiency seen in HIV infection.
**Why the Correct Answer is Right**
HIV specifically targets and infects CD4+ T lymphocytes, also known as T helper cells. These cells play a central role in coordinating the immune response, activating other immune cells, and producing cytokines that facilitate the immune response. The virus binds to the CD4 receptor on the surface of these cells, facilitating its entry and replication. As a result, the depletion of CD4+ T cells leads to a weakened immune system, making the individual susceptible to opportunistic infections and diseases.
**Why Each Wrong Option is Incorrect**
**Option A:** Macrophages are another type of immune cell that can be infected by HIV, but they are not the primary target cells. Macrophages play a role in the immune response, but their depletion is not as directly responsible for the immunodeficiency seen in HIV infection.
**Option B:** Neutrophils are a type of white blood cell that is primarily involved in the innate immune response, particularly in the defense against bacterial infections. They are not the primary target cells for HIV infection.
**Option C:** Dendritic cells are antigen-presenting cells that play a crucial role in the adaptive immune response, but they are not the primary target cells for HIV infection.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the CD4 count is a critical marker of HIV disease progression and is used to determine the severity of immunodeficiency. A CD4 count below 200 cells/μL indicates advanced HIV disease and a significant risk of opportunistic infections.
**Correct Answer:** C. CD4+ T lymphocytes.