Natural antibodies against alliinase in human serum and polyclonal antibodies elicited in rabbit share the same immunogenic determinants

Human serum contains natural antibodies against alliinase, a protein abunda ntly found in garlic (Allium sativum) cloves. In order to study the epitope (s) of this protein recognized by anti-alliinase antibodies, we used a rand om hexapeptide library displayed on filamentous M13 phage. Analysis of the phagotopes selected on rabbit anti-alliinase antibodies revealed that the m otif-GKXVXX- was common for all peptides. The most frequent phage displayin g -GKHVAV- sequence has a 50% identity with the original alliinase sequence (amino acid residues 156-161). The position of this epitope is only nine a mino acids apart from the oligosaccharide chain attached to the N-146. The rabbit anti-alliinase immunoglobulin G (IgG), which bound the phages displa ying this phagotope, also bound the corresponding peptide derived from the alliinase sequence. Affinity-purified natural antibodies against alliinase, present in normal human serum (which can specifically recognize the native and denaturated protein) also bound the selected phagotope. Thus. our resu lts indicate that specific natural anti-dietary protein antibodies presente d in human serum can have the same, or overlapping, epitopes with the IgG e voked during the active (experimental) immunization in animals. (C) 1000 El sevier Science B.V. All rights reserved.