**Question:** EBV infects B cells binding to

A. CD21
B. CD40
C. CD70
D. CD32

**Core Concept:** Epstein-Barr virus (EBV) is a lymphotropic herpesvirus that primarily infects B cells, leading to various clinical manifestations including infectious mononucleosis and lymphoproliferative disorders. EBV infection involves binding of the virus to specific receptors on the host cell surface, followed by viral entry and replication.

**Why the Correct Answer is Right:** EBV binds to CD21, which is a complement receptor expressed on the surface of B cells. This binding event triggers the internalization of EBV into the host cell, initiating the infection process.

**Why Each Wrong Option is Incorrect:**

A. CD40: CD40 is a receptor involved in B cell activation, rather than viral entry. EBV does not bind to CD40.
B. CD40: Similar to CD40, CD40 is not the receptor responsible for EBV entry into B cells.
C. CD70: CD70 is a ligand involved in T cell activation, not a receptor for EBV binding.
D. CD32: CD32 is a receptor primarily associated with the immune response to bacterial infections, not involved in EBV entry into B cells.

**Clinical Pearl:** The correct binding receptor for EBV on B cells (CD21) is crucial for understanding the infection process and pathogenesis of EBV-related diseases. Familiarizing yourself with the other incorrect options can help identify similar viruses or infections that target different cell types and receptors.

**Correct Answer:** A. CD21

**Why CD21 is Right:** CD21, also known as complement receptor 2 (CR2), is the correct receptor for EBV binding to B cells. This interaction allows EBV to enter the host cell, initiating infection and leading to the development of various EBV-related diseases.