Efalizumab disrupts the interaction between which of the following adhesion molecules?
**Core Concept**
Efalizumab is a recombinant humanized monoclonal antibody that targets **CD11a**, a subunit of **LFA-1 (Lymphocyte Function-Associated Antigen 1)**, which is an adhesion molecule expressed on the surface of **T lymphocytes**. This interaction is crucial for the migration and activation of T cells.
**Why the Correct Answer is Right**
Efalizumab works by binding to **CD11a**, thereby disrupting its interaction with **ICAM-1 (Intercellular Adhesion Molecule 1)**, which is expressed on the surface of **antigen-presenting cells**. This disruption prevents the activation and migration of T cells into the skin, making it useful in treating conditions like **psoriasis**.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while **VCAM-1 (Vascular Cell Adhesion Molecule 1)** is an adhesion molecule, it is not the primary target of efalizumab.
**Option B:** Incorrect as **CD11b** is part of the **Mac-1** integrin, not the target of efalizumab.
**Option C:** Incorrect because **CD11c** is part of the **CR4** integrin and is not targeted by efalizumab.
**Clinical Pearl / High-Yield Fact**
Remember, efalizumab's mechanism of action involves disrupting **LFA-1/ICAM-1** interaction, which is crucial for T cell activation and migration, making it a therapeutic option for **T cell-mediated diseases**.
**Correct Answer:** D. LFA-1/ICAM-1.