Immunogenicity of Actinobacillus ApxIA toxin epitopes fused to the E-coli heat-labile enterotoxin B subunit

Peptides KDYGASTGSSL (Epi1), SLLRRRRNGEDVSV (Epi3) and DDEIYGNDGHP (Epi6), predicted to constitute immunogenic epitopes of the hemolysin-cytotoxin Apx IA of Actinobacillus pleuropneumoniae were inserted into a surface-exposed loop of the B subunit of the E. coli heat-labile enterotoxin (EtxB). The re sulting chimeric proteins were recognized by monospecific antibodies agains t purified native ApxI and by convalescent sera of pigs that were positive for A. pleuropneumoniae serotype 1. Mice anti-sera against chimeric protein s EtxB::ApxIAEpi3 and EtxB::ApxIAEpi6 reacted with purified ApxI. These res ults indicate that Epi3 and Epi6 regions constitute linear epitopes of the structural ApxIA protein toxin. Epitope Epi6 which is located in the struct ure of the glycine rich repeats in ApxI elicits the formation of hemolysin neutralizing antibodies when introduced into mice in the form of a chimeric EtxB fusion protein. We suggest that fusion of peptide sequences to EtxB i s a useful tool for the analysis of epitopes of complex proteins such as RT X toxins. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.