EPITOPE MAPPING OF THE SITE(S) OF BINDING OF FC-EPSILON-RII CD23 WITHIN HUMAN IGE - DETERMINATION OF THE B-LYMPHOCYTE-BINDING SITES BY USE OF SYNTHETIC PEPTIDES AND ANTIPEPTIDE ANTIBODIES REPRESENTATIVE OF LINEAR FC SEQUENCES/

The work undertaken has investigated the structure-function relationsh ip between IgE and its low affinity receptor on B lymphocytes. To iden tify sites on the IgE molecule which interact with the low affinity re ceptor (Fc epsilon RII/CD23), 10 different peptide sequences within th e CH2, CH3 and CH4 domains of human IgE were selected according to cha rge, overall hydrophobicity and possible accessibility on native IgE s equences. Peptides representative of these were synthesized by the sol id phase procedure; and their cytophilic activities were examined by d etermining their capacity to inhibit the binding of radiolabelled or e rythrocyte-bound IgE to a Fc epsilon RII/CD23 positive B cell line (RP MI-8866). Moreover, these linear sequences were rendered immunogenic b y conjugation to a protein carrier (KLH) and used to produced polyclon al antibodies in rabbits. The reactivity of the anti-peptide antibodie s with both free peptides and native IgE bound to a solid phase, as we ll as their capacity to inhibit binding of IgE to a Fc epsilon RII/CD2 3 positive cell line, were investigated. Results from such use of pept ides and anti-peptide antibodies indicate that two sequences, represen tative of residues 364-383 and 401-415, could be involved in the bindi ng of IgE to both membrane-bound and soluble form Fc epsilon RII/CD23; indicating that the B lymphocyte-binding site on human IgE may be res tricted to the CH3 domain.