**Question:** EBV infects -

A. Epstein-Barr Nuclear Antigen (EBNA)
B. Epstein-Barr Virus (EBV)
C. Latent Membrane Protein (LMP)
D. CD4+ T cells

**Correct Answer:** D. CD4+ T cells

**Core Concept:**
Epstein-Barr virus (EBV) is a human gamma-herpesvirus that is closely associated with various human diseases, including infectious mononucleosis, Burkitt's lymphoma, and Nasopharyngeal carcinoma. EBV primarily infects B cells, which are a type of white blood cell crucial for adaptive immunity, specifically CD4+ T cells.

**Why the Correct Answer is Right:**
EBV primarily infects resting B cells, which express CD40 ligand (CD40L) on their surface. CD40L interacts with CD40 on B cells, leading to B cell activation and proliferation. This interaction is crucial for the activation of B cells and subsequent immune response, including antibody production. Since EBV infects B cells, the correct answer is CD4+ T cells (CD40L+ cells).

**Why Each Wrong Option is Incorrect:**
A. Epstein-Barr Nuclear Antigen (EBNA) is a viral protein expressed within infected cells, not the cell type that EBV infects.
B. Epstein-Barr Virus (EBV) is a virus, not a cell type. The correct answer is CD4+ T cells.
C. Latent Membrane Protein (LMP) is a viral protein expressed in the latent phase of EBV infection, not the cell type the virus infects.

**Clinical Pearl:**
Infectious mononucleosis, also known as "mono," is a common viral infection caused by EBV, which is transmitted through saliva. During mono, the virus targets CD4+ T cells, causing their dysfunction and resulting in the characteristic symptoms of fever, fatigue, and lymphadenopathy. This underlines the importance of CD4+ T cells in maintaining immune homeostasis and fighting off infections.