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Infection and Immunity, April 2000, p. 2196-2204, Vol. 68, No. 4
Department of
Microbiology1 and Interdisciplinary
Graduate Program in Immunology,2 The
University of Iowa, Iowa City, Iowa 52242
Received 2 September 1999/Returned for modification 14 October
1999/Accepted 7 January 2000
Sublethal infection of mice with recombinant Listeria
monocytogenes expressing a model epitope in either secreted or
nonsecreted form results in similar CD8+ T-cell priming.
Since nonsecreted bacterial proteins have no obvious access to the
endogenous major histocompatibility complex (MHC) class I presentation
pathway, presentation of these antigens requires destruction of the
bacterium to reveal the nonsecreted molecules to an exogenous MHC class
I presentation pathway. Gamma interferon (IFN-
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Copyright © 2000, American Society for Microbiology. All rights reserved.
CD8+ T-Cell Priming against a Nonsecreted
Listeria monocytogenes Antigen Is Independent of the
Antimicrobial Activities of Gamma Interferon
), a cytokine made by
multiple cell types in response to L. monocytogenes
infection, could be required for exogenous presentation of nonsecreted
bacterial antigens via its capacity to upregulate the expression of
molecules involved in antigen presentation, its capacity to activate
macrophages to kill bacteria to expose nonsecreted molecules or both.
IFN-
knockout (KO) mice were used to address the requirement for
IFN-
in CD8+ T-cell priming against (i) a model
exogenous antigen and (ii) secreted and nonsecreted L. monocytogenes antigens. We demonstrate that IFN-
KO mice are
capable of cross-presenting the model exogenous antigen ovalbumin to
prime CD8+ T-cell responses that are only slightly weaker
than that in wild-type (WT) mice. Despite their extreme susceptibility
to primary L. monocytogenes infection, previously immunized
and naive IFN-
KO mice were able to generate CD8+ T-cell
responses against both secreted and nonsecreted L. monocytogenes antigens which were similar to responses of WT
mice. Interestingly, IFN-
KO mice were as capable as WT mice in
mediating the characteristic drop in bacterial load in the liver at
4 h postinfection, although the IFN-
KO mice have exacerbated
bacterial loads as early as 24 h postinfection. These results
demonstrate that the regulatory functions of IFN-
are not required
for priming of CD8+ T cells by cross-presentation of a
model exogenous antigen or in response to a nonsecreted L. monocytogenes antigen. In addition, the capacity of IFN-
to
activate the microbicidal activities of macrophages is not required for
the very early innate immune response to L. monocytogenes
or priming of CD8+ T cells against a nonsecreted bacterial antigen.
*
Corresponding author. Mailing address: Department of
Microbiology, University of Iowa, Iowa City, IA 52242. Phone: (319)
335-9720. Fax: (319) 335-9006. E-mail: john-harty{at}uiowa.edu.
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