Study on antigenicity of peptides mimotopes of S.Typhi lipopolysaccharide

Objective To study the antigenicity of 3 peptides which mimic lipopolysaccharide (LPS) epitope. Methods Three peptide mimotopes of LPS, linear P12 (GPPQWFFSQPQL), cyclic 13a (SACPSWASFWCGG), and cyclic 13b (SACFQFYPAACGG), were synthesized and conjugated to carrier protein of keyhole limpet haemocyanin or blue carrier. The binding of peptide-carrier to anti-LPS antibody was identified by ELISA. The inhibitions of free synthetic peptides on binding between anti-LPS antibody and LPS, and on binding between anti-LPS antibody and phage clones mimicing epitopes of LPS were identified by competitive ELISA. Results Peptide-carrier could bind to anti-LPS antibody. Free peptide 13a could inhibit the binding of anti-LPS monoclonal antibody (mAb) to LPS (IC_ 50 = 125 μg/mL) and the binding of phage clone K1 to anti-LPS mAb (IC_ 50 = 15.6 μg/mL). Free peptide P12 could inhibit the binding of anti-LPS mAb to LPS (IC_ 50 = 550 μg/mL) and the binding of phage clone P1 to anti-LPS mAb (IC_ 50 = 375 μg/mL). Free peptide 13b could inhibit the binding of phage clone P4 to polyclonal anti-LPS antibody. Conclusion The results demonstrate that synthesized peptides mimotopes of LPS have the antigenicity of LPS epitopes, and that the antigenicity of cylcic peptide is better than that of linear peptide.