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

• Published in: Infection and Immunity 1996-08, Vol.64 (8), p.3341-3350
• Main Authors: BROWN, W. C, MCELWAIN, T. F, RUEF, B. J, SUAREZ, C. E, SHKAP, V, CHITKO-MCKOWN, C. G, TUO, W, RICE-FICHT, A. C, PALMER, G. H
• Format: Article
• Language: English
• Subjects: Animals; Antigens, Protozoan - classification; Antigens, Protozoan - genetics; Antigens, Protozoan - immunology; Babesia bigemina; Babesia bovis; Babesia bovis - classification; Babesiosis - epidemiology; Babesiosis - immunology; Base Sequence; Biological and medical sciences; Cattle; Cattle Diseases - epidemiology; Cattle Diseases - immunology; Clone Cells; Conserved Sequence; Cytokines - biosynthesis; Epitopes - immunology; Erythrocytes - parasitology; Fundamental and applied biological sciences. Psychology; Immunity; Immunodominant Epitopes; Life cycle. Host-agent relationship. Pathogenesis; linfocitos; lymphocyte; Lymphocyte Activation; lymphocytes; Molecular Sequence Data; Protozoa; Protozoan Proteins - classification; Protozoan Proteins - genetics; Protozoan Proteins - immunology; Recombinant Proteins - immunology; T-Lymphocytes, Helper-Inducer - immunology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.64.8.3341-3350.1996

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 immunosorbent 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.