title: Analysis of molecular diversity of the Trypanosoma cruzi trypomastigote small surface antigen reveals novel epitopes, evidence of positive selection and potential implications for lineage-specific serology.
abstract: Chagas disease, marked by life-long chronic infection with Trypanosoma cruzi, remains a major parasitic disease in Latin America. Genetically heterogeneous, T. cruzi is divided into six discrete typing units (DTUs), most recently grouped as TcI-VI. The trypomastigote small surface antigen (TSSA) of T. cruzi has been described as the only known serological marker to identify infection by TcII-VI, as distinct from TcI. Here, by comparative analysis of a cohort of 25 reference strains representing all the known DTUs, we show that TSSA intra-specific diversity is greater than previously reported. Furthermore, TcIII and IV TSSA PCR products are, contrary to expectation, both digested by PvuII, revealing a more nuanced genotyping pattern. Amino acid sequence diversity reveals that the TSSA epitope considered to be serologically characteristic of TcII-VI is restricted to TcII, V and VI, but not of III or IV, and that the diagnostic peptide described as TcI-specific shares key features with TcIII and IV. Notably, TSSA sequences inferred greater phylogenetic affinities of TcIII and IV to TcI than to TcII, V or VI. A high ratio of non-synonymous to synonymous nucleotide substitutions (omega=1.233) indicates that the TSSA gene has been under positive selection pressure. The demonstration of lineage-specific epitopes within TcII-VI has implications for sero-epidemiological studies of Chagas disease based on this antigen.
authors.affiliation: Pathogen Molecular Biology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E7HT, UK. Tapan.Bhattacharyya@lshtm.ac.uk
authors.forename: Tapan
authors.initials: T
authors.lastname: Bhattacharyya
authors.forename: Jessica
authors.initials: J
authors.lastname: Brooks
authors.forename: Matthew
authors.initials: M
authors.lastname: Yeo
authors.forename: Hernan J
authors.initials: HJ
authors.lastname: Carrasco
authors.forename: Michael D
authors.initials: MD
authors.lastname: Lewis
authors.forename: Martin S
authors.initials: MS
authors.lastname: Llewellyn
authors.forename: Michael A
authors.initials: MA
authors.lastname: Miles
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000954:Antigens, Surface / Q000235:genetics / Q000276:immunology*; D014355:Chagas Disease / Q000276:immunology* / Q000469:parasitology*; D016000:Cluster Analysis; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D000939:Epitopes / Q000235:genetics / Q000276:immunology*; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D007843:Latin America; D008969:Molecular Sequence Data; D010802:Phylogeny; D012641:Selection, Genetic; D016415:Sequence Alignment; D014349:Trypanosoma cruzi / Q000235:genetics / Q000276:immunology* / Q000302:isolation & purification
chemical_list: D000954:Antigens, Surface; D016054:DNA, Protozoan; D000939:Epitopes