Babesia bovis rhoptry-associated protein 1 is immunodominant for T helper cells of immune cattle and contains T-cell epitopes conserved among geographically distant B. bovis strains.
The ability of rhoptry-associated protein 1 (RAP-1) of Babesia bovis and Babesia bigemina to confer partial protective immunity in cattle has stimulated interest in characterizing both B-cell and T-cell epitopes of these proteins. It was previously shown that B. bovis RAP-1 associates with the merozoite surface as well as rhoptries and expresses B-cell epitopes conserved among otherwise antigenically different B. bovis strains. An amino-terminal 307-amino-acid domain of the molecule that is highly conserved in the B. bigemina RAP-1 homolog did not contain cross-reactive B-cell epitopes. The studies reported here demonstrate that B. bovis RAP-1 is strongly immunogenic for T helper (Th) cells from B. bovis-immune cattle and that like B-cell epitopes, Th-cell epitopes are conserved in different B. bovis strains but not in B. bigemina RAP-1. Lymphocytes from cattle immune to challenge with the Mexico strain of B. bovis proliferated against recombinant B. bovis RAP-1 protein derived from the Mexico strain. T-cell lines established by stimulating lymphocytes with recombinant RAP-1 protein responded against B. bovis, but not B. bigemina, merozoites. T-cell lines established by repeated stimulation of lymphocytes with B. bovis membrane antigen proliferated strongly against RAP-1, demonstrating the immunodominant nature of this protein. RAP-1-specific CD4+ T cell clones recognized Mexico, Texas, Australia, and Israel strains of B. bovis but neither B. bigemina merozoites nor recombinant B. bigemina RAP- 1. Analysis of cytokine mRNA in RAP-1-specific Th cell clones revealed strong expression of gamma interferon but little or no expression of interleukin-2 (IL-2), IL-4, or IL-10. Gamma interferon production was confirmed by enzyme-linked imunosorbent assay. These results indicate the potential to use selected B. bovis RAP-1 peptides as immunogens to prime for strong, anamnestic, strain-cross-reactive type 1 immune responses upon exposure to B. bovis.
Brown
W C
WC
Department of Veterinary Pathiobiology, Texas A & M University, College Station 77843, USA.
McElwain
T F
TF
Ruef
B J
BJ
Suarez
C E
CE
Shkap
V
V
Chitko-McKown
C G
CG
Tuo
W
W
Rice-Ficht
A C
AC
Palmer
G H
GH
D000818:Animals; D000953:Antigens, Protozoan / Q000145:classification / Q000235:genetics / Q000276:immunology*; D016793:Babesia bovis / Q000145:classification; D001404:Babesiosis / Q000453:epidemiology / Q000276:immunology*; D001483:Base Sequence; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000276:immunology*; D002999:Clone Cells; D017124:Conserved Sequence; D016207:Cytokines / Q000096:biosynthesis; D000939:Epitopes / Q000276:immunology; D004912:Erythrocytes / Q000469:parasitology; D007109:Immunity; D016056:Immunodominant Epitopes; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000145:classification / Q000235:genetics / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*
D000953:Antigens, Protozoan; D016207:Cytokines; D000939:Epitopes; D016056:Immunodominant Epitopes; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C065352:rhoptry associated protein, Plasmodium