MAPPING EPITOPES FOR 20 MONOCLONAL-ANTIBODIES TO CR-1

Complement receptor type one (CR1; CD35) binds and processes C3b and C 4b opsonized immune complexes and regulates complement activation. We have characterized the epitopes of 13 previously reported and seven ne w MoAbs to human CR1. The MoAbs formed seven groups based on their rea ctivity with a panel of deletion forms of CR1. Seventeen of the MoAbs reacted with CR1 at more than one site, a consequence of its repetitiv e sequence. All five of the MoAbs recognizing epitopes in the nearly i dentical repeats 3, 10, and 17, as well as one MoAb which reacted with repeats 8 or 1/2 of 9 and 15 or 1/2 of 16, blocked cofactor activity for C3b. Knowledge of the repeats bearing the epitopes for these MoAbs should facilitate the further characterization of CR1.