HIV affects -a) Only T helper cellsb) T helper and macrophagesc) NK cellsd) B – lymphocytes

**Core Concept**
HIV (Human Immunodeficiency Virus) primarily targets and infects specific immune cells, leading to a compromised immune response. This infection primarily affects cells expressing the CD4 receptor, a crucial component of the immune system.

**Why the Correct Answer is Right**
The correct answer is that HIV affects T helper cells and macrophages. This is because both cell types express the CD4 receptor on their surface, which serves as the primary entry point for HIV. Upon infection, HIV integrates its genetic material into the host cell's genome, leading to the destruction of these cells and a subsequent decline in immune function. This results in the characteristic immunodeficiency syndrome associated with HIV infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while T helper cells are the primary target of HIV, the virus also infects macrophages, which express the CD4 receptor as well.

**Option C:** Incorrect because NK (Natural Killer) cells are not typically infected by HIV. NK cells are part of the innate immune system and do not express the CD4 receptor.

**Option D:** Incorrect because B-lymphocytes, which are responsible for producing antibodies, do not typically express the CD4 receptor and are therefore not the primary target of HIV infection.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the primary target of HIV is the CD4+ T cell, and a CD4 count below 200 cells/μL is often used as a diagnostic criterion for AIDS. This is crucial for understanding the pathophysiology of HIV and the clinical manifestations of AIDS.

**Correct Answer: B. T helper and macrophages.**