Loss of Immunization-Induced Epitope-Specific CD4 T-Cell Response following Anaplasma marginale Infection Requires Presence of the T-Cell Epitope on the Pathogen and Is Not Associated with an Increase in Lymphocytes Expressing Known Regulatory Cell Phenotypes.
We have shown that in cattle previously immunized with outer membrane proteins, infection with Anaplasma marginale induces a functionally exhausted CD4 T-cell response to the A. marginale immunogen. Furthermore, T-cell responses following infection in nonimmunized cattle had a delayed onset and were sporadic and transient during persistent infection. The induction of an exhausted T-cell response following infection presumably facilitates pathogen persistence. In the current study, we hypothesized that the loss of epitope-specific T-cell responses requires the presence of the immunizing epitope on the pathogen, and T-cell dysfunction correlates with the appearance of regulatory T cells. In limited studies in cattle, regulatory T cells have been shown to belong to γδ T-cell subsets rather than be CD4 T cells expressing forkhead box protein P3 (FoxP3). Cattle expressing the DRB3*1101 haplotype were immunized with a truncated A. marginale major surface protein (MSP) 1a that contains a DRB3*1101-restricted CD4 T-cell epitope, F2-5B. Cattle either remained unchallenged or were challenged with A. marginale bacteria that express the epitope or with A. marginale subsp. centrale that do not. Peripheral blood and spleen mononuclear cells were monitored for MSP1a epitope F2-5B-specfic T-cell proliferative responses and were stained for γδ T-cell subsets or CD4(+) CD25(+) FoxP3(+) T cells before and during infection. As hypothesized, the induction of T-cell exhaustion occurred only following infection with A. marginale, which did not correlate with an increase in either CD4(+) CD25(+) FoxP3(+) T cells or any γδ T-cell subset examined.
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA wbrown@vetmed.wsu.edu.
Wendy C
WC
Brown
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.
Joshua E
JE
Turse
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.
Paulraj K
PK
Lawrence
Animal Diseases Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, Washington, USA.
Wendell C
WC
Johnson
Animal Diseases Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, Washington, USA.
Glen A
GA
Scoles
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.
James R
JR
Deringer
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.
Eric L
EL
Sutten
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.
Sushan
S
Han
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.
Junzo
J
Norimine
D042322:Anaplasma marginale / Q000276:immunology*; D000712:Anaplasmosis / Q000276:immunology* / Q000517:prevention & control*; D000818:Animals; D002417:Cattle; D049109:Cell Proliferation; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D007108:Immune Tolerance; D007114:Immunization / Q000379:methods*; D016130:Immunophenotyping; D010641:Phenotype; D016176:T-Lymphocyte Subsets / Q000276:immunology*
D018984:Epitopes, T-Lymphocyte