Immunodominant epitopes in Babesia bovis rhoptry-associated protein 1 that elicit memory CD4(+)-T-lymphocyte responses in B. bovis-immune individuals are located in the amino-terminal domain.
Babesia bovis rhoptry-associated protein 1 (RAP-1), which confers partial protection against B. bovis challenge, is recognized by antibodies and T lymphocytes from cattle that have recovered from infection and are immune to subsequent challenge. RAP-1 is a 60-kDa protein with an N-terminal (NT) region that contains four cysteine residues conserved among all Babesia RAP-1 family members and a C-terminal (CT) region that contains multiple, degenerate, tandem 23-amino-acid (aa) repeats. To define the location of CD4(+)-T-cell epitopes for vaccine development using a recombinant protein or minigene construct, a series of truncated recombinant RAP-1 proteins and peptides were tested for stimulation of T-cell lines derived from B. bovis-immune cattle. CD4(+)-T-cell lines from three B. bovis-immune cattle with different DRB3 haplotypes responded to the NT region of RAP-1, whereas T cells from only one animal responded weakly to the CT region. T-cell lines from the three individuals recognized two to six NT-region peptides spanning aa 134 to 316 and representing at least four dominant epitopes. Using RAP-1-specific CD4(+)-T-cell clones, two NT-region epitopes, EYLVNKVLYMATMNYKT (aa 187 to 203) and EAPWYKRWIKKFR (aa 295 to 307), and one CT-region repeat epitope, FREAPQATKHFL, which is present twice at aa positions 391 to 402 and 414 to 425, were identified. Several peptides representing degenerate repeats of the agonist CT-region peptide FREAPQATKHFL neither stimulated responses of T-cell clones specific for this peptide nor inhibited responses to the agonist peptide. Upon stimulation with specific antigen, T-cell clones specific for NT or CT epitopes produced gamma interferon. The presence of T-helper-cell epitopes in the NT domain of RAP-1, which is highly conserved among otherwise antigenically different strains of B. bovis, supports the inclusion of this region in vaccine constructs to be tested in cattle.
Norimine
Junzo
J
Program in Vector-Borne Diseases, Department of Veterinary Microbiology and Pathology Animal Disease Research Unit, Washington State University, Pullman, Washington 99164, USA.
Suarez
Carlos E
CE
McElwain
Terry F
TF
Florin-Christensen
Monica
M
Brown
Wendy C
WC
D000595:Amino Acid Sequence; D000818:Animals; D016793:Babesia bovis / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002417:Cattle; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D016056:Immunodominant Epitopes; D007156:Immunologic Memory; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000737:chemistry / Q000276:immunology*
D018984:Epitopes, T-Lymphocyte; D000949:Histocompatibility Antigens Class II; D016056:Immunodominant Epitopes; D015800:Protozoan Proteins; C097551:rhoptry-associated protein-1, Babesia