Genetic polimorphism and differential expression of genes encoding Antigen B from Echinococcus granulosus. PRIMER PREMIO AREA HELMINTOS

KAMENETZKY L.; MUZULIN P. M.; GUTIERREZ A. M.; ANGEL S. O.; ZAHA A.; GUARNERA E. A.; ROSENZVIT M. C.

Florianópolis Brasil

Congreso; XLI Congreso de la Sociedad Brasilera de Medicina Tropical y I Encuentro de Medicina Tropical del Cono Sur; 2005

Sociedad Brasilera de Medicina Tropical

Echinococcus granulosus, the causative agent of cystic hydatid disease, exists as a number of intraspecific variants that differ in biological characters, such as intermediate host specificity and infectivity to humans.  One of the major antigens of the larval stage of the parasite, the antigen B (AgB), is widely used in diagnosis and has been involved in the evasion of host immune response. We used PCR-SSCP followed bysequencing to evaluate the intraspecific variation and expression profile of five genes of the AgB family. The strains analyzed were: Sheep, Tasmanian sheep, Cattle, Camel and Pig strains. Forty two genomic sequences were isolated and clustered in five genes (B1 to 5) by maximum parsimony analysis. The variants were differentially distributed among strains. AgB1 and AgB4- related variants were present in almost all strains, whereas AgB2-related sequences were present as functional genes in sheep and Tasmanian sheep strains but as pseudogenes in cattle, camel and pig strains. Some variants clustered in a differential node near to AgB3 and AgB5 sequences. We named them AgB3-like. AgB5 was present only in sheep strain. Neutrality was rejected for functional AgB2-related sequences. Intra-strain variation was also observed, mainly in sheep strain. Echinococcus granulosus, the causative agent of cystic hydatid disease, exists as a number of intraspecific variants that differ in biological characters, such as intermediate host specificity and infectivity to humans.  One of the major antigens of the larval stage of the parasite, the antigen B (AgB), is widely used in diagnosis and has been involved in the evasion of host immune response. We used PCR-SSCP followed bysequencing to evaluate the intraspecific variation and expression profile of five genes of the AgB family. The strains analyzed were: Sheep, Tasmanian sheep, Cattle, Camel and Pig strains. Forty two genomic sequences were isolated and clustered in five genes (B1 to 5) by maximum parsimony analysis. The variants were differentially distributed among strains. AgB1 and AgB4- related variants were present in almost all strains, whereas AgB2-related sequences were present as functional genes in sheep and Tasmanian sheep strains but as pseudogenes in cattle, camel and pig strains. Some variants clustered in a differential node near to AgB3 and AgB5 sequences. We named them AgB3-like. AgB5 was present only in sheep strain. Neutrality was rejected for functional AgB2-related sequences. Intra-strain variation was also observed, mainly in sheep strain. The level of nucleotide and amino acid variation observed is higher than the reported so far for coding genes of other helminth parasites. Differential expression of AgB variants between protoscoleces of sheep and pig strains was detected by RT-PCR. Sheep strain expressed AgB2 and AgB4 variants, sharing 68% of amino acid identity, while pig strain only expressed AgB4-related sequences. Preliminary expression analysis of AgB1, 3 and 5 also showed differences between this strains. These data demonstrate for the first time the genetic variability of antigen-coding genes among genetically characterised strains of E. granulosus.