Selection of high-affinity single-chain antibodies to human C3 by phage display

C3 is the key protein in the activation of the complement system, and it contributes to an effective immune response. However, C3 is also targeted by autoantibodies during the development of autoimmune diseases such as systemic lupus erythematosus, and the autoantigenicity of C3 is still poorly understood. In order to study the molecular aspects of C3 autoantigenicity and the localization of C3 autoepitopes, we selected high-affinity anti-C3 antibodies from the “Griffin 1” phage display library expressing human scFv antibodies. The rounds of phage selection were performed with a gradual decrease in the amount of the antigen C3, resulting in the selection of forty clones of recombinant anti-C3 scFv antibodies. Quantitative ELISA analysis determined four high-affinity monoclonal scFvs to C3, and their expression was optimized with IPTG induction and autoinduction methods. Dot blot analysis revealed that the selected high-affinity anti-C3 clones recognized C3 and its smaller fragments C3b and C3c, but not C3d.