Description:CD21, also known as CR2 (complement receptor 2) and C3d receptor, binds C3d and iC3b. It is also a receptor of Epstein-Barr virus. CD35, also known as CR1, binds C3b, iC3b, C4b, and iC4b. CD21/CD35 is primarily expressed on B lymphocytes, mast cells, follicular dendritic cells, macrophages, and activated granulocytes. CD21/CD35 forms part of the B-cell antigen receptor complex with CD19 and CD81 and is involved in signal transduction.