title: Two Theileria parva CD8 T cell antigen genes are more variable in buffalo than cattle parasites, but differ in pattern of sequence diversity.
abstract: BACKGROUND
  Theileria parva causes an acute fatal disease in cattle, but infections are asymptomatic in the African buffalo (Syncerus caffer). Cattle can be immunized against the parasite by infection and treatment, but immunity is partially strain specific. Available data indicate that CD8(+) T lymphocyte responses mediate protection and, recently, several parasite antigens recognised by CD8(+) T cells have been identified. This study set out to determine the nature and extent of polymorphism in two of these antigens, Tp1 and Tp2, which contain defined CD8(+) T-cell epitopes, and to analyse the sequences for evidence of selection.
  
  
  RESULTS
  Partial sequencing of the Tp1 gene and the full-length Tp2 gene from 82 T. parva isolates revealed extensive polymorphism in both antigens, including the epitope-containing regions. Single nucleotide polymorphisms were detected at 51 positions (∼12%) in Tp1 and in 320 positions (∼61%) in Tp2. Together with two short indels in Tp1, these resulted in 30 and 42 protein variants of Tp1 and Tp2, respectively. Although evidence of positive selection was found for multiple amino acid residues, there was no preferential involvement of T cell epitope residues. Overall, the extent of diversity was much greater in T. parva isolates originating from buffalo than in isolates known to be transmissible among cattle.
  
  
  CONCLUSIONS
  The results indicate that T. parva parasites maintained in cattle represent a subset of the overall T. parva population, which has become adapted for tick transmission between cattle. The absence of obvious enrichment for positively selected amino acid residues within defined epitopes indicates either that diversity is not predominantly driven by selection exerted by host T cells, or that such selection is not detectable by the methods employed due to unidentified epitopes elsewhere in the antigens. Further functional studies are required to address this latter point.
authors.affiliation: International Livestock Research Institute, Nairobi, Kenya. r.pelle@cgiar.org
authors.forename: Roger
authors.initials: R
authors.lastname: Pelle
authors.forename: Simon P
authors.initials: SP
authors.lastname: Graham
authors.forename: Moses N
authors.initials: MN
authors.lastname: Njahira
authors.forename: Julius
authors.initials: J
authors.lastname: Osaso
authors.forename: Rosemary M
authors.initials: RM
authors.lastname: Saya
authors.forename: David O
authors.initials: DO
authors.lastname: Odongo
authors.forename: Philip G
authors.initials: PG
authors.lastname: Toye
authors.forename: Paul R
authors.initials: PR
authors.lastname: Spooner
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Musoke
authors.forename: Duncan M
authors.initials: DM
authors.lastname: Mwangi
authors.forename: Evans L N
authors.initials: EL
authors.lastname: Taracha
authors.forename: W Ivan
authors.initials: WI
authors.lastname: Morrison
authors.forename: William
authors.initials: W
authors.lastname: Weir
authors.forename: Joana C
authors.initials: JC
authors.lastname: Silva
authors.forename: Richard P
authors.initials: RP
authors.lastname: Bishop
mesh_terms: D000818:Animals; D002020:Buffaloes; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology* / Q000469:parasitology*; D002417:Cattle; D002460:Cell Line; D000939:Epitopes / Q000737:chemistry; D019143:Evolution, Molecular; D014644:Genetic Variation; D005838:Genotype; D016366:Open Reading Frames; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D016797:Theileria parva / Q000235:genetics*; D013801:Theileriasis / Q000469:parasitology*
chemical_list: D000939:Epitopes