Epitope specificity of antibodies raised against enterotoxigenic Escherichia coli CFA/I fimbriae in mice immunized with naked DNA.

The cfaB gene, coding for the CFA/I fimbrial adhesin of enterotoxigenic Escherichia coli (ETEC), was cloned and expressed as a fusion peptide with the glycoprotein D (gD) from herpes simplex virus type 1 (HSV) in the pRE4 eukaryotic expression vector, resulting in the recombinant plasmid pRECFA. All BALB/c mice injected intramuscularly (i.m.) with a single dose (100 micrograms) of the purified plasmid developed antibodies against epitopes found on dissociated CFA/I subunits as well as other homologous ETEC fimbriae. Surface-exposed epitopes found on intact CFA/I fimbriae were also recognized by antibodies derived from DNA immunization, but they did not overlap with those generated with purified CFA/I fimbriae. None of the sera raised in mice immunizated with pRECFA were able to agglutinate bacterial cells or inhibit haemagglutination promoted by CFA/I bearing ETEC cells. These results show that pRECFA can elicit CFA/I-specific antibodies, which may have different epitope specificities and functional properties compared with those generated with purified bacterial protein.