title: MyD88-dependent signaling contributes to host defense against ehrlichial infection.
abstract: The ehrlichiae are small gram-negative obligate intracellular bacteria in the family Anaplasmataceae. Ehrlichial infection in an accidental host may result in fatal diseases such as human monocytotropic ehrlichiosis, an emerging, tick-borne disease. Although the role of adaptive immune responses in the protection against ehrlichiosis has been well studied, the mechanism by which the innate immune system is activated is not fully understood. Using Ehrlichia muris as a model organism, we show here that MyD88-dependent signaling pathways play a pivotal role in the host defense against ehrlichial infection. Upon E. muris infection, MyD88-deficient mice had significantly impaired clearance of E. muris, as well as decreased inflammation, characterized by reduced splenomegaly and recruitment of macrophages and neutrophils. Furthermore, MyD88-deficient mice produced markedly lower levels of IL-12, which correlated well with an impaired Th1 immune response. In vitro, dendritic cells, but not macrophages, efficiently produced IL-12 upon E. muris infection through a MyD88-dependent mechanism. Therefore, MyD88-dependent signaling is required for controlling ehrlichial infection by playing an essential role in the immediate activation of the innate immune system and inflammatory cytokine production, as well as in the activation of the adaptive immune system at a later stage by providing for optimal Th1 immune responses.
authors.affiliation: Department of Cancer Immunology & AIDS, Dana-Farber Cancer Institute, Boston, Massachusetts, United States of America.
authors.forename: Young-Sang
authors.initials: YS
authors.lastname: Koh
authors.forename: Jung-Eun
authors.initials: JE
authors.lastname: Koo
authors.forename: Amlan
authors.initials: A
authors.lastname: Biswas
authors.forename: Koichi S
authors.initials: KS
authors.lastname: Kobayashi
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000276:immunology / Q000382:microbiology; D004536:Ehrlichia / Q000276:immunology* / Q000472:pathogenicity*; D005434:Flow Cytometry; D018664:Interleukin-12 / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology
chemical_list: D053594:Myeloid Differentiation Factor 88; D018664:Interleukin-12