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Infection and Immunity, January 2002, p. 380-388, Vol. 70, No. 1
0019-9567/01/$04.00+0     DOI: 10.1128/IAI.70.1.380-388.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Persistent Ehrlichia chaffeensis Infection Occurs in the Absence of Functional Major Histocompatibility Complex Class II Genes{dagger}

Roman Reddy Ganta,1* Melinda J. Wilkerson,1 Chuanmin Cheng,1 Aaron M. Rokey,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 5 September 2001/ Accepted 3 October 2001

Human monocytic ehrlichiosis is an emerging tick-borne disease caused by the rickettsia Ehrlichia chaffeensis. We investigated the impact of two genes that control macrophage and T-cell function on murine resistance to E. chaffeensis. Congenic pairs of wild-type and toll-like receptor 4 (tlr4)- or major histocompatibility complex class II (MHC-II)-deficient mice were used for these studies. Wild-type mice cleared the infection within 2 weeks, and the response included macrophage activation and the synthesis of E. chaffeensis-specific Th1-type immunoglobulin G response. The absence of a functional tlr4 gene depressed nitric oxide and interleukin 6 secretion by macrophages and resulted in short-term persistent infections for >=30 days. In the absence of MHC-II alleles, E. chaffeensis infections persisted throughout the entire 3-month evaluation period. Together, these data suggest that macrophage activation and cell-mediated immunity, orchestrated by CD4+ T cells, are critical for conferring resistance to 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.ksu.edu.

{dagger} This work is contribution 01-279-5-J of the Agricultural Experimental Station.

Editor: J. T. Barbieri

Infection and Immunity, January 2002, p. 380-388, Vol. 70, No. 1
0019-9567/01/$04.00+0     DOI: 10.1128/IAI.70.1.380-388.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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