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Reference.org
Complement receptor 2
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<p>Complement receptor type 2 (CR2), also known as complement C3d receptor, Epstein–Barr virus receptor, and CD21 (cluster of differentiation 21), is a <a href="/facts/Protein/Jxmagu3E">protein</a> that in humans is encoded by the CR2 <a href="/facts/Gene/e1swwPY6">gene</a>. </p><p>CR2 is involved in the <a href="/facts/Complement_system/vRSrQDUv">complement system</a>. It binds to <a href="/facts/IC3b/oD7WlMVY">iC3b</a> (inactive derivative of <a href="/facts/C3b/gQ2bfe0R">C3b</a>), C3dg, or C3d. <a href="/facts/B_cell/6Y1tgwwp">B cells</a> express CR2 on their surfaces, allowing the complement system to play a role in B-cell activation and maturation. </p>