Role of toll-like receptor 4 in protection by bacterial lipopolysaccharide in the nasal mucosa of atopic children but not adults

doi:10.1016/S0140-6736(04)16253-3

The Lancet

Volume 363, Issue 9422, 22 May 2004, Pages 1689-1697

https://doi.org/10.1016/S0140-6736(04)16253-3 Get rights and content

Summary

Background

Exposure to bacterial products in early life could protect against development of atopy. We examined the effect of bacterial lipopolysaccharide on allergic inflammation and expression of cytokines and lipopolysaccharide receptor (toll-like receptor 4; TLR4) in nasal mucosa of 15 atopic children and ten atopic adults.

Methods

Explanted mucosa was cultured with allergen with or without lipopolysaccharide (0·1 mg/L) for 24 h. Immunocytochemistry and in-situ hybridisation were used to phenotype the cells and cytokines.

Findings

In explants from atopic children, lipopolysaccharide prevented allergen-induced T-helper type 2 (Th2) inflammation and upregulated Th1 cytokine reactivity and expression. These effects were blocked by antibody to interleukin 10. In children but not in adults, lipopolysaccharide caused increases of three times in T-cell reactivity, five times in T-cell proliferation, and four times in expression of interleukin 10 compared with mucosa stimulated with allergen alone. This difference in response was mirrored by lipopolysaccharide-induced increases in TLR4 reactivity in children but not adults. TLR4 receptor was expressed by CD3-positive T cells, and TLR4-positive cells contained interleukin 10. Lipopolysaccharide increased expression of cells positive for both CD3 and TLR4; both TLR4 and interleukin 10; and both CD4 and CD25.

Interpretation

Lipopolysaccharide inhibits allergic inflammation in nasal mucosa of atopic children by skewing local immune responses from Th2 to Th1 and upregulating production of interleukin 10. These effects are mediated by TLR4. Our results emphasise an important difference between adults and children in their ability to respond to bacterial products. These differences could have a role in normal maturation of the immune system.

Introduction

The hygiene hypothesis suggests that decreasing exposure to infections or bacterial products is the cause of the increasing incidence of atopy and asthma.1, 2, 3 Epidemiological studies have consistently shown that the farming environment is protective in young children against development of hayfever, atopy, and wheeze. Bacterial lipopolysaccharide has been suggested as a potential mediator of these protective effects.4, 5, 6, 7 Although epidemiological evidence supports the role of bacterial lipopolysaccharide in the hygiene hypothesis, the mechanisms of any lipopolysaccharide-induced immunomod-ulation or modification of an allergic immune response during early life are poorly understood.

We have shown previously that although exposure of rats to lipopolysaccharide during early sensitisation protects against their development of ovalbumin-specific IgE,⁸ coexposure of lipopolysaccharide with allergen results in dose-dependent inhibition of acute and late-phase allergic inflammation and bronchial hyper-responsiveness;⁹ exposure to lipopolysaccharide after allergen challenge further exacerbates the allergic response.⁸ The effect of lipopolysaccharide depended on the timing of exposure and the dose given. We have shown lately that administration of lipopolysaccharide to explanted nasal mucosa of young non-atopic children shifts the immune response towards a T-helper 1 (Th1) phenotype by causing inflammatory cell activation and promoting strong proliferation of T cells.¹⁰ This model shows many of the features of in-vivo lipopolysaccharide-induced inflammation previously described in both animals and human beings, including cellular activation, production of cytokines, and mast-cell degranulation. Importantly, these effects of lipopolysaccharide were mediated locally without recruitment of inflammatory cells from the systemic circulation.

To investigate further the effect of lipopolysaccharide on allergic inflammation in the nasal mucosa of young atopic children, we used the above explant model to compare the responses with those in atopic adults. We decided to stimulate the allergic mucosa simultaneously with allergen and lipopolysaccharide to mimic the normal environmental exposure more closely, because both of these antigens are ubiquitous contaminants in the environment. We hypothesised that lipopolysaccharide can downregulate the allergen-induced local inflammation in the nasal mucosa of atopic children by causing a shift from a Th2 towards a Th1 immune response and inducing production of the immunoregulatory cytokine interleukin 10.

Section snippets

Participants

22 children and 17 adults were recruited for this study. 15 atopic children (mean age 3·2 years [SD 0·4]) and seven non-atopic children (mean age 3·8 years [0·7]) of both sexes were recruited from the ear, nose, and throat clinic at the Montreal Children's Hospital. Atopy was confirmed by skin-prick testing to a panel of common allergens including housedust mite, grass pollen, ragweed extract, and cat and dog antigens. Non-atopic children had no history of asthma or other allergic diseases and

Results

In non-stimulated atopic mucosa of children, we detected constitutively expressed CD68, major basic protein, elastase, tryptase, CD3, interleukin 2, and CD25. Similarly, constitutive expression of mRNA for both Th2 (interleukins 4, 5, 13, and 10) and Th1 (interferon γ, interleukin 12) cytokines was detected in this tissue.

Exposure of atopic mucosa to lipopolysaccharide without allergen significantly increased the number of cells immunoreactive for CD68 (p=0·0009), elastase (p=0·01), tryptase

Discussion

We have extended our previous studies with an ex-vivo human model of lipopolysaccharide-induced inflammation in explanted nasal mucosa from non-atopic children to show that administration of lipopolysaccharide can skew the local allergic response in young atopic children away from a Th2 towards a Thl immune response. The shift in cytokine profile is associated with increased production of immunoregulatory interleukin 10, proliferation of CD3-positive T lymphocytes and increased numbers of

GLOSSARY

cytokines: A family of small, low-molecular-weight proteins involved in intercellular signalling, growth, proliferation, and cell death.
hygiene hypothesis: The idea that low exposure to bacterial products, especially during early life, might be the reason for the increasing incidence of asthma.
lipopolysaccharide: A major component of the cell wall of gram-negative bacteria.
toll-like receptor 4: A receptor involved in lipopolysaccharide-induced signal transduction.

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Mechanisms of DiseaseRole of toll-like receptor 4 in protection by bacterial lipopolysaccharide in the nasal mucosa of atopic children but not adults

Summary

Background

Methods

Findings

Interpretation

Introduction

Section snippets

Participants

Results

Discussion

GLOSSARY

Lancet

J Allergy Clin Immunol

J Allergy Clin Immunol

J Allergy Clin Immunol

J Allergy Clin Immunol

J Allergy Clin Immunol

J Biol Chem

Asthma: an epidemic in the absence of infection?

Science

Environmental factors and primary T-cell sensitisation to inhalant allergens in infancy: reappraisal of the role of infections and air pollution

Pediatr Allergy Immunol

Reduced risk of hay fever and asthma among children of farmers

Clin Exp Allergy

Austrian children living on a farm have less hay fever, asthma and allergic sensitization

Clin Exp Allergy

Farm environment in childhood prevents the development of allergies

Clin Exp Allergy

Lower risk of allergic sensitisation and hay fever in farmers' children in Switzerland

Epidemiology

Modification of the inflammatory response to allergen challenge following exposure to bacterial lipopolysaccharide

Am J Respir Cell Mol Biol

Modification of acute and late-phase allergic responses to ovalbumin with lipopolysaccharide

Int Arch Allergy Immunol

Expression of endothelin-1 in lungs of patients with cryptogenic fibrosing alveolitis

Lancet

Mechanisms of Disease
Role of toll-like receptor 4 in protection by bacterial lipopolysaccharide in the nasal mucosa of atopic children but not adults