CHARACTERIZATION OF C3DG BINDING TO A RECESS FORMED BETWEEN SHORT CONSENSUS REPEATS 1 AND 2 OF COMPLEMENT RECEPTOR-TYPE 2 (CR-2, CD21)

To allow for a better characterization of tbe Ligand binding structure s of human complement receptor type 2 (CR2; CD21), we have established an IgG1 kappa mouse mAb, FES, that interferes efficiently with bindin g of C3dg and EBV to CR2, In contrast to mAb OKB7, the only well-chara cterized mAb with similar specificity, mAb FE8 blocked binding of solu ble C3dg or particles carrying multiple copies of surface-bound C3dg t o CR2 or induced complete removal of these ligands from the receptor, In vitro EBV infection of B lymphocytes, on the other hand, was abroga ted by mAbs FE8 and OKB7 with similar dose-response characteristics. A s FE8 was shown to recognize a discontinuous epitope, a series of over lapping peptides derived from SCR1 and -2 and immobilized on cellulose was screened with FE8. The results suggest that up to five discontinu ous sequences contributed to the epitope, The sequence 63-EYFNKYS-69, located between the two SCR units, reacted most intensively. Two other sequences, 16-YYSTPI-21 and 105-NGNKSVWCQANN-116, are located between Cys(1) and Cys(2) of SCR1 and around Cys(3) of SCR2, respectively, Ba sed on the solution structure For two factor Il SCRs, a three-dimensio nal model of SCR1 and -2 was generated, The FE8 binding peptide sequen ces were located in relative proximity to each other, bounding the rec ess formed between SCR1 and -2, This potential of mAb FE8 is currently unique and may be exploited for interfering with conditions of unwant ed recognition of C3dg-coated structures by the immune system.