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Infection and Immunity, January 2004, p. 159-167, Vol. 72, No. 1
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.1.159-167.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Delayed Clearance of Ehrlichia chaffeensis Infection in CD4+ T-Cell Knockout Mice{dagger}

Roman R. Ganta,1* Chuanmin Cheng,1 Melinda J. Wilkerson,1 and Stephen K. Chapes2

Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine,1 Division of Biology, College of Arts and Sciences, Kansas State University, Manhattan, Kansas 665062

Received 25 July 2003/ Returned for modification 22 September 2003/ Accepted 20 October 2003

Human monocytic ehrlichiosis is an emerging tick-borne disease caused by the rickettsia Ehrlichia chaffeensis. To examine the role of helper T cells in host resistance to this macrophage-tropic bacterium, we assessed E. chaffeensis infections in three mouse strains with differing functional levels of helper T cells. Wild-type, C57BL/6J mice resolved infections in approximately 2 weeks. Major histocompatibility complex class II (MHCII) knockout, B6.129-Abbtm1 mice lacking helper T cells developed persistent infections that were not resolved even after several months. CD4+ T-cell-deficient, B6.129S6-Cd4tm1Knw mice cleared the infection, but the clearance took 2 weeks longer than it did for wild-type mice. C57BL/6J mice resolved infection more rapidly following a second experimental challenge, but B6.129S6-Cd4tm1Knw mice did not. The B6.129S6-Cd4tm1Knw mice also developed active E. chaffeensis-specific immunoglobulin G responses that were slightly lower in concentration and slower to develop than that observed in C57BL/6J mice. E. chaffeensis-specific cytotoxic T cells were not detected following a single bacterial challenge in any mouse strain, including wild-type C57BL/6J mice. However, the cytotoxic T-cell activity developed in all three mouse strains, including the MHCII and CD4+ T-cell knockouts, when challenged with a second E. chaffeensis infection. The data reported here suggest that the cell-mediated immunity, orchestrated by CD4+ T cells is critical for conferring rapid clearance of E. chaffeensis.

* Corresponding author. Mailing address: Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, 1800 Denison Ave., Manhattan, KS 66506. Phone: (785) 532-4612. Fax: (785) 532-4851. E-mail: rganta{at}vet.k-state.edu.

{dagger} Kansas Agricultural Experiment Station publication no. 04-021-J.

Editor: J. T. Barbieri

Infection and Immunity, January 2004, p. 159-167, Vol. 72, No. 1
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.1.159-167.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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