Toll-Like Receptor–Dependent Activation of Antigen-Presenting Cells Affects Adaptive Immunity to Helicobacter pylori

doi:10.1053/j.gastro.2007.04.071

Gastroenterology

Volume 133, Issue 1, July 2007, Pages 150-163.e3

https://doi.org/10.1053/j.gastro.2007.04.071 Get rights and content

Background & Aims: Recognition of infection leads to induction of adaptive immunity through activation of antigen-presenting cells (APCs). Among APCs, dendritic cells (DCs) have the unique capacity to deliver antigens from the periphery to T cells in secondary lymphoid organs. Methods: We analyzed molecular mechanisms of the Helicobacter pylori–induced APC activation in vitro and investigated the influence of Myd88 signaling on the phenotype of adaptive immunity to H pylori in a murine infection model. Results: The adaptor protein Myd88 mediates Toll-like receptor (TLR), interleukin (IL)-1, and IL-18 signaling. DCs from wild-type, IL-1R^−/−, and IL-18^−/− mice responded to H pylori with secretion of proinflammatory cytokines and up-regulation of major histocompatibility complex II and costimulatory molecules. In Myd88^−/− DCs these processes were impaired profoundly, showing that TLR-dependent H pylori–sensing affects DC activation. Analysis of the H pylori–specific DC transcriptome revealed that large parts of the bacteria-induced transcriptional changes depended on Myd88 signaling, comprising numerous genes involved in crucial steps of immune regulation, such as DC maturation/differentiation, antigen uptake/presentation, and effector cell recruitment/activation. The impaired ability of Myd88^−/− DCs, B cells, and macrophages to mount a proinflammatory response to H pylori in vitro was reflected in vivo by reduced gastric inflammation and increased bacterial colonization in Myd88-deficient mice. Furthermore, Helicobacter-specific IgG2c/IgG1 ratios were reduced in Myd88^−/− animals, suggesting the involvement of the Myd88-dependent pathway in the instruction of adaptive immunity toward a T helper cell type 1 phenotype. Conclusions: A principal pathway by which DCs sense H pylori and become activated is the TLR-dependent signaling cascade. In vivo, Myd88 signaling affects adaptive immunity to the bacterium.

Section snippets

Bacteria

The mouse-adapted H pylori strain SS1 was used for mouse inoculation experiments. For stimulation of DCs we used the H pylori strains SS1, Hp76, and G27. Bacteria were grown at 37°C under microaerophilic conditions (85% N₂, 10% CO₂, and 5% O₂) on Wilkins Chalgren agar plates (Oxoid, Basingstoke, England). Agar plates were supplemented with 10% horse serum (Gibco, Eggenstein, Germany) and a standard Helicobacter-selective antibiotic mixture (DENT supplement; Oxoid). For quantitative H pylori

Interaction of H pylori With Mouse BMDCs

To investigate the different steps of the Helicobacter/DC interaction we generated mouse BMDCs. Figure 1A shows GFP-transformed H pylori G27 adhering to a DC after 15 minutes of incubation. Large numbers of bacteria remained adherent even after extensive washing (10×), showing the strength of binding. Uptake of bacteria or microbial components by DCs is important for subsequent antigen processing and presentation. Figure 1B shows confocal microscopic images of extracellularly and

Discussion

The adaptive immune system, found exclusively in vertebrates, evolved from an ancient innate defense mechanism common to all metazoans. It is therefore not surprising that innate immune sensing and signaling is the starting point of specific immunity. Central to this process are the DCs that integrate innate information and convey it to lymphocytes.¹¹ We show here that DC activation by H pylori is mediated largely by TLRs. H pylori–stimulated Myd88^−/− DCs, but not wild-type, IL-18^−/−, or IL-1R

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: Current address for R.R.: The Wellcome Trust Sanger Institute, Genome Campus, CB10 1SA Hinxton/Cambridge, United Kingdom. email: [email protected]

¹: R.R. is a recipient of a fellowship from the German Research Society and obtained financial support from Bund der Freunde der Technischen Universität München. The Microarray and Bioinformatics Core Unit at the Institute of Medical Microbiology, Immunology and Hygiene is supported by the Bundesministerium für Bildung und Forschung (Nationales Genomforschungsnetz Network Infection and Inflammation FKZ 01G0113, TP 37 to R.L., H.W., and R. Hoffmann).

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Basic–alimentary tractToll-Like Receptor–Dependent Activation of Antigen-Presenting Cells Affects Adaptive Immunity to Helicobacter pylori

Section snippets

Bacteria

Interaction of H pylori With Mouse BMDCs

Discussion

Lancet

Gastroenterology

J Immunol Methods

Biochem Biophys Res Commun

Cell

J Biol Chem

J Biol Chem

Microbes Infect

Mol Immunol

Am J Pathol

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Basic–alimentary tract
Toll-Like Receptor–Dependent Activation of Antigen-Presenting Cells Affects Adaptive Immunity to Helicobacter pylori