Acta Tropica 75 (2000) 331–340 Comparative analysis of two different subunits of antigen B from Echinococcus granulosus : gene sequences, expression in Escherichia coli and serological evaluation Marilise B. Rott a , Vero ´ nica Ferna ´ndez b , Sandra Farias c , Janine Ceni d , Henrique B. Ferreira d , Karen L. Haag e , Arnaldo Zaha d, * a Departamento de Microbiologia, Instituto de Cie ˆncias Ba ´sicas da Sau ´de, Uniersidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil b Ca ´tedra de Inmunologia, Facultad de Qu ´imica, Uniersidad de la Repu ´blica, Casilla de Correo 1157, Monteideo, Uruguay c Departamento de Fisiologia, Instituto de Cie ˆncias Ba ´sicas da Salu ´de, Uniersidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil d Centro de Biotecnologia and Departamento de Biologia Molecular e Biotecnologia, Uniersidade Federal do Rio Grande do Sul, Caixa Postal 15005, Porto Alegre, 91501 -970, RS, Brazil e Departamento de Ge ´nitica, Instituto de Biocie ˆncias, Uniersidade Federal do Rio Grande do Sul, Caixa Postal 15053, Porto Alegre, 91501 -970, RS, Brazil Received 25 May 1999; received in revised form 21 January 2000; accepted 7 February 2000 Abstract Two different Echinococcus granulosus antigen B subunits (AgB8/1 and AgB8/2) were characterized and the structure of the genes encoding these two proteins were compared. DNA sequences were expressed in Escherichia coli and the antigens’ diagnostic value was then assessed. The genomic sequence of AgB8/1 has a 92 bp intron in the position corresponding to amino acid 16; the AgB8/2 genomic sequence presents a 68 bp intron in the position corresponding to amino acid 20. Both introns are located between the putative N-terminal hydrophobic sequence and the secreted peptide. A comparison between the AgB8/1 and AgB8/2 nucleotide sequences showed a 53.5% identity among exons and a 50% identity between introns. According to the molecular diversity analysis, the elapsed time since both genes shared a common ancestor would be around 4.2 ×10 7 years. When the native AgB and the two recombinant antigens (rAgB8/1 and rAgB8/2) were tested in an anti-IgG ELISA, the sensitivity of the native antigen B was 77.41% and its specificity was 81.9%, while rAgB8/1 showed 54.84% of sensitivity and 80.17% of specificity and rAg138/2 had an 83.87% sensitivity and a 98.28% specificity. Statistical analysis confirms that rAgB8/2 has a better performance than rAgB8/1 and native AgB in ELISA. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Echinococcus granulosus ; Antigen B; Recombinant antigens; Sequence analysis; Serodiagnosis; ELISA www.elsevier.com/locate/actatropica * Corresponding author. Tel.: +55-51-3166086; fax: +55-51-3191079. E-mail address: zaha@dna.cbiot.ufrgs.br (A. Zaha) 0001-706X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0001-706X(00)00069-3