High polymorphism in genes encoding antigen B from human infecting strains of Echinococcus granulosus
Echinococcus granulosus antigen B (AgB) is encoded by a gene family and is involved in the evasion of the host immune response. E. granulosus exists as a number of strains (G1–G10) that differ in biological characteristics. We used PCR-SSCP followed by DNA sequencing to evaluate sequence variation and transcription profile of AgB in 5 E. granulosus strains 1 . Twenty-four genomic sequences were isolated and clustered in 3 groups related to 2 of the 5 reported AgB genes. AgB4 genes were present in almost all strains, whereas AgB2 were present as functional genes exclusively in G1/G2 cluster, and as non-functional genes in G5 and the G6/G7 cluster, suggesting inter-strain variation. The AgB transcription patterns, analysed by RT-PCR, showed that AgB2 and AgB4 genes were transcribed in G1, while only the AgB4 gene was transcribed in G7 strain. Cysts from the same strain or cluster shared more genomic and cDNA variants than cysts from different strain or cluster. The level of nucleotide and deduced amino acid sequence variation observed is higher than that reported so far for coding genes of other helminths. Neutrality was rejected for AgB2 genes. These data show the genetic polymorphism of antigen-coding genes among genetically characterized strains of E. granulosus.(Received April 22 2005)
(Revised May 26 2005)
(Accepted May 28 2005)
Key Words: genetic polymorphism; antigen B; Echinococcus granulosus; strains; RT-PCR; SSCP.
c1 Departamento de Parasitología, Instituto Nacional de Enfermedades Infecciosas ANLIS “Dr. Carlos G. Malbrán” Av. Velez Sarsfield 563, Buenos Aires (1281), Argentina. Fax: +5411 43032382. E-mail: email@example.com
1 Nucleotide sequence data reported in this paper are available in the GenBankTM database under the Accession numbers AY569341-AY569371, AY159484, AY159485, AY608606, AY608607, AY614001.