Hemoparasitic diseases remain endemic in most tropical and semitropical areas of the world. Development of effective vaccines for malarial and newly emerging babesial parasites has been partly constrained by the lack of relevant outbred animal models. Immunoregulatory mechanisms in cattle are much more like those of humans than mice, so this outbred large animal species provides an alternative system to study the mechanisms of protective immunity against protozoan parasites. The pathology of-Babesia bovis infection in cattle is very similar to that caused by Plasmodium falciparum infections in humans, and is characterized by a generalized circulatory disturbance and sequestration of parasitized erythrocytes in the capillary beds, especially in the brain. Cattle recovered from natural or experimental infection with viable tick- or blood-borne stages of B. bovis develop long-lived protective immunity against subsequent exposure to both homologous and heterologous parasite strains, which correlates with the in vitro development of a Th1 response. Immunization with killed parasites or fractionated merozoite antigen has also resulted in variable degrees of protective immunity against homologous and heterologous challenge, which does not correlate with a specific humoral response. Furthermore, attempts to select vaccine antigens based on serological immunodominance have failed to identify protective immunogens. Because cell-mediated immune effector mechanisms are crucial for the induction of protective immunity against many intracellular parasites, and induction of Type 1 (T1 or Th1) helper cells correlates with immunity to B. bovis and related malarial parasites, we propose an alternative method for identifying protective protozoan parasite antigens based on the capacity to induce T1 responses in immune animals. We hypothesize that antigens selected for in vitro stimulation of T1 responses will stimulate protective immunity in vivo. Th1 cells will be used as probes to identify potentially protective antigens of B. bovis. Th cell lines and clones derived from immune cattle and characterized for cytokine expression patterns will be used in proliferation assays to identify biochemically fractionated parasite antigens. Antisera raised against these partially purified proteins will be used to identify the genes encoding the stimulatory T cell proteins by screening a B. bovis expression library. Alternatively, T cell lines and clones will be used directly to screen the library. Selected recombinant proteins will then be tested for the capacity to induce protective immunity in cattle and to characterize the nature of the T cell, macrophage and antibody responses both in vitro and in vivo against the immunogen. These studies will provide insight into the cellular and molecular basis of protective immunity against antigens that naturally stimulate a Th1 response in immune cattle, which will be directly applicable to related babesial and malarial parasites of humans.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI030136-09
Application #
2672023
Study Section
Tropical Medicine and Parasitology Study Section (TMP)
Project Start
1990-08-01
Project End
2001-05-31
Budget Start
1998-06-01
Budget End
1999-05-31
Support Year
9
Fiscal Year
1998
Total Cost
Indirect Cost
Name
Washington State University
Department
Veterinary Sciences
Type
Schools of Veterinary Medicine
DUNS #
041485301
City
Pullman
State
WA
Country
United States
Zip Code
99164
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Goff, Will L; McElwain, Terry F; Suarez, Carlos E et al. (2003) Competitive enzyme-linked immunosorbent assay based on a rhoptry-associated protein 1 epitope specifically identifies Babesia bovis-infected cattle. Clin Diagn Lab Immunol 10:38-43
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Norimine, Junzo; Suarez, Carlos E; McElwain, Terry F et al. (2002) 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. Infect Immun 70:2039-48
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Brown, W C; Ruef, B J; Norimine, J et al. (2001) A novel 20-kilodalton protein conserved in Babesia bovis and B. bigemina stimulates memory CD4(+) T lymphocyte responses in B. bovis-immune cattle. Mol Biochem Parasitol 118:97-109
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Shoda, L K; Palmer, G H; Florin-Christensen, J et al. (2000) Babesia bovis-stimulated macrophages express interleukin-1beta, interleukin-12, tumor necrosis factor alpha, and nitric oxide and inhibit parasite replication in vitro. Infect Immun 68:5139-45
Ruef, B J; Ward, T J; Oxner, C R et al. (2000) Phylogenetic analysis with newly characterized Babesia bovis hsp70 and hsp90 provides strong support for paraphyly within the piroplasms. Mol Biochem Parasitol 109:67-72
Tuo, W; Palmer, G H; McGuire, T C et al. (2000) Interleukin-12 as an adjuvant promotes immunoglobulin G and type 1 cytokine recall responses to major surface protein 2 of the ehrlichial pathogen Anaplasma marginale. Infect Immun 68:270-80

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