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TLR Ligands Differentially Modulate T Cell Responses to Acute and Chronic Antigen Presentation¹

Nevil J. Singh^2,*, Maureen Cox and Ronald H. Schwartz^*

^* Laboratory of Cellular and Molecular Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and Department of Microbiology, University of Alabama, AL 35294

The outcome of peripheral T cell activation is thought to be largely determined by the context in which the cognate Ag is initially presented. In this framework, microbial products that can activate APCs via TLRs are considered critical in converting an otherwise tolerogenic context to an immunogenic one. We examine this idea using a model system where naive T cells are stimulated in the periphery by a persistent self Ag. The addition of multiple TLR ligands to this context, acutely or chronically, failed to significantly alter the tolerogenic phenotype in the responding T cells. This contrasts with the ability of such adjuvants to improve T cell responses to soluble peptide immunizations. We reconcile this difference by revealing a hitherto poorly appreciated property of TLR ligands, which extends the duration of soluble Ag presentation in vivo by an additional two to three days. Finally, we could replace the requirement for TLR-mediated APC activation in soluble-Ag-induced T cell expansion and differentiation, by maintaining the Ag depot in vivo using repeated immunizations. These data suggest a novel process by which TLR ligands modulate T cell responses to acute Ags, without disrupting the induction of tolerance to persistent self Ags.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by the Intramural Research Program of the National Institutes of Allergy and Infectious Diseases, National Institutes of Health.

² Address correspondence and reprint requests to Dr. Nevil J. Singh, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Building 4, Room 111, 4 Center Drive, Bethesda, MD 20892. E-mail address: nsingh{at}niaid.nih.gov

³ Abbreviations used in this paper: PAMP, pathogen-associated molecular pattern; PCC, pigeon cytochrome C.