Immunogen sequence: VIRYSCSGTF RLIGEKSLLC ITKDKVDGTW DKPAPKCEYF NKYSSCPEPI VPGGYKIRGS TPYRHGDSVT FACKTNFSMN GNKS. CD21 (complement receptor 2, CR2, C3D receptor, EBV receptor) binds C3 complement fragments, especially its breakdown fragments, which remai