Identification of two Th1 cell epitopes on the Babesia bovis-encoded 77-kilodalton merozoite protein (Bb-1) by use of truncated recombinant fusion proteins.
Previous studies have demonstrated the serologic and T-cell immunogenicity for cattle of a recombinant form of the apical complex-associated 77-kDa merozite protein of Babesia bovis, designated Bb-1. The present study characterizes the immunogenic epitopes of the Bb-1 protein. A series of recombinant truncated fusion proteins spanning the majority of the Bb-1 protein were expressed in Escherichia coli, and their reactivities with bovine peripheral blood mononuclear cells and T-cell clones derived from B. bovis-immune cattle and with rabbit antibodies were determined. Lymphocytes from two immune cattle were preferentially stimulated by the N-terminal half of the Bb-1 protein (amino acids 23 to 266, termed Bb-1A), localizing the T-cell epitopes to the Bb-1A portion of the molecule. CD4+ T-cell clones derived by stimulation with the intact Bb-1 fusion protein were used to identify two T-cell epitopes in the Bb-1A protein, consisting of amino acids SVVLLSAFSGN VWANEAEVSQVVK and FSDVDKTKSTEKT (residues 23 to 46 and 82 to 94). In contrast, rabbit antiserum raised against the intact fusion protein reacted only with the C-terminal half of the protein (amino acids 267 to 499, termed Bb-1B), which contained 28 tandem repeats of the tetrapeptide PAEK or PAET. Biological assays and Northern (RNA) blot analyses for cytokines revealed that following activation with concanavalin A, T-cell clones reactive against the two Bb-1A epitopes produced interleukin-2, gamma interferon, and tumor necrosis factors beta and alpha, but not interleukin-4, suggesting that the Bb-1 antigen preferentially stimulates the Th1 subset of CD4+ T cells in cattle. The studies described here report for the first time the characterization, by cytokine production, of the Th1 subset of bovine T cells and show that, as in mice, protozoal antigens can induce Th1 cells in ruminants. This first demonstration of B. bovis-encoded Th1 cell epitopes provides a rationale for incorporation of all or part of the Bb-1 protein into a recombinant vaccine.
Brown
W C
WC
Department of Veterinary Pathobiology, Texas A&M University, College Station 77843.
Zhao
S
S
Woods
V M
VM
Tripp
C A
CA
Tetzlaff
C L
CL
Heussler
V T
VT
Dobbelaere
D A
DA
Rice-Ficht
A C
AC
D000595:Amino Acid Sequence; D000818:Animals; D016793:Babesia bovis; D001404:Babesiosis / Q000276:immunology*; D015152:Blotting, Northern; D002417:Cattle; D002418:Cattle Diseases / Q000276:immunology*; D016207:Cytokines / Q000096:biosynthesis; D004306:Dose-Response Relationship, Immunologic; D000939:Epitopes / Q000737:chemistry*; D007111:Immunity, Cellular; D008213:Lymphocyte Activation / Q000276:immunology; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D015800:Protozoan Proteins / Q000276:immunology*; D012313:RNA / Q000032:analysis; D011993:Recombinant Fusion Proteins / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D016207:Cytokines; D000939:Epitopes; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C078913:77 kDa merozoite protein, Babesia; D012313:RNA