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. 2009 Aug;16(8):1158-69.
doi: 10.1128/CVI.00092-09. Epub 2009 Jun 3.

Selection of polymorphic peptides from GRA6 and GRA7 sequences of Toxoplasma gondii strains to be used in serotyping

Susana Sousa  1 , Daniel Ajzenberg, Maggy Marle, Dominique Aubert, Isabelle Villena, José Correia da Costa, Marie-Laure Dardé
Affiliations

Selection of polymorphic peptides from GRA6 and GRA7 sequences of Toxoplasma gondii strains to be used in serotyping

Susana Sousa et al. Clin Vaccine Immunol. 2009 Aug.

Abstract

The evaluation of Toxoplasma gondii isolates obtained from geographical environments other than Europe and North America revealed the existence of atypical strains that are not included in the three archetypal clonal lineages (lineages I, II, and III). GRA6 and GRA7 are polymorphic genes that have been used for the genotyping of Toxoplasma. The coding regions of GRA6 and GRA7 from 49 nonarchetypal strains were sequenced and compared with the sequences of type I, II, and III reference strains. Eighteen and 10 different amino acid sequences were found for GRA6 and GRA7, respectively. The polymorphisms found between the different sequences were analyzed, with the objective of defining peptides to be used for the serotyping of Toxoplasma infections. Two peptides specific for clonal lineages I and III (peptides GRA7I and GRA7III, respectively) were selected from the GRA7 locus. Three peptides specific for some atypical strains (peptides Am6, Af6, and Am7) were selected from both the GRA6 and the GRA7 loci. Serum samples from humans infected with Toxoplasma strains of known genotypes were serotyped with the selected peptides. Peptide GRA7III seems to be a good candidate for the serotyping of infections caused by type III strains. Peptide GRA7I had a very low sensitivity. Peptides Am6 and Af6 had low specificities, since they reacted with serum samples from patients infected with strains belonging to the three archetypal lineages. Although peptide Am7 was specific, it had low sensitivity.

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Figures

FIG. 1.
FIG. 1.
Pattern of reactivity of serum samples from patients infected with type I, II, and III and atypical strains when they were tested against peptide GRA7I. Horizontal lines represent the cutoff values (the cutoff values are different for sera for Europe and South America).
FIG. 2.
FIG. 2.
Pattern of reactivity of serum samples from patients infected with type I, II, and III and atypical strains when they were tested against peptide GRA7III. Horizontal lines represent the cutoff values.
FIG. 3.
FIG. 3.
Pattern of reactivity of serum samples from patients infected with type I, II, and III and atypical strains when they were tested against peptide Am6. Horizontal lines represent the cutoff values (the cutoff values are different for sera from Europe and South America).
FIG. 4.
FIG. 4.
Pattern of reactivity of serum samples from patients infected with type I, II, and III and atypical strains when they were tested against peptide Af6. Horizontal lines represent the cutoff values.
FIG. 5.
FIG. 5.
Pattern of reactivity of serum samples from patients infected with type I, II, and III and atypical strains when they were tested against peptide Am7. Horizontal lines represent the cutoff values (the cutoff values are different for sera from Europe and South America).
FIG. 6.
FIG. 6.
Pattern of reactivity of serum samples from patients infected with type I, II, and III and atypical strains when they were tested against the antigen from the whole-cell extract. Horizontal lines represent the cutoff values.
See this image and copyright information in PMC

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