Toll-Like Receptor Modulation in Allergic Airway Inflammation

Toll-like receptors (TLRs) are pivotal innate immune sensors that detect conserved microbial and endogenous molecular patterns, initiating signalling cascades that shape both innate and adaptive responses in the respiratory tract. In allergic airway inflammation, TLRs expressed on epithelial cells, dendritic cells, macrophages and recruited monocytes can exert dichotomous effects. Engagement of certain TLRs during allergen sensitisation may skew the immune environment away from a T-helper 2 (Th2)-dominated response toward Th1 or Th17 profiles, thereby attenuating eosinophilic inflammation and airway hyperresponsiveness (AHR). Conversely, activation of distinct TLRs during established allergic inflammation or viral co-infection can amplify airway obstruction through enhanced cytokine release, neutrophil recruitment and remodelling of the airway wall. Modulation of TLR pathways therefore offers a dual therapeutic opportunity: to prevent allergic sensitisation by promoting regulatory circuits and to ameliorate exacerbations by counteracting pathogen-driven amplification of type 2 inflammation. Recent work has illuminated the cell-specific roles of TLR3, TLR4, TLR7 and TLR9 in shaping cytokine networks, influencing dendritic cell maturation, regulating T-regulatory cell expansion and controlling stromal cell activation within the lung. As a result, tailored TLR agonists or antagonists are under investigation as adjuvants in allergen immunotherapy, as inhaled innate immune stimulants for broad-spectrum protection and as novel agents to restore immune balance in severe or steroid-resistant asthma phenotypes.

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Toll-Like Receptor Modulation in Allergic Airway Inflammation publication trend

The graph below shows the total number of articles in toll-like receptor modulation in allergic airway inflammation across all publications each year (not limited to Nature Index journals).

Technical terms

Toll-like receptor (TLR): A class of pattern-recognition receptors that detect pathogen-associated or damage-associated molecular patterns and initiate innate immune signalling.

Agonist: A substance that binds to a receptor and triggers its biological activity, mimicking the effect of a natural ligand.

Airway hyperresponsiveness (AHR): An exaggerated constrictive response of the airways to stimuli, characteristic of asthma and allergy-related lung disease.

Bronchoalveolar lavage fluid (BALF): Fluid obtained from rinsing the lung’s airspaces, used to analyse immune cells and soluble mediators in airway inflammation.

T-helper (Th) cells: Subsets of CD4+ T lymphocytes (e.g. Th1, Th2, Th17) that orchestrate distinct types of adaptive immune responses, with Th2 cells driving allergic inflammation.

References

1. Toll-like receptor activation induces airway obstruction and hyperresponsiveness in guinea pigs. Respiratory Research (2024).
2. Imiquimod powder for inhalation to stimulate innate immunity. Journal of Drug Delivery Science and Technology (2024).
3. Activation of TLR Signaling in Sensitization-Recruited Inflammatory Monocytes Attenuates OVA-Induced Allergic Asthma. Frontiers in Immunology (2018).
4. Dual Role of Toll-like Receptors in Human and Experimental Asthma Models. Frontiers in Immunology (2018).