Allergic airway recall responses require IL-9 from resident memory CD4⁺ T cells

Area of Science:

• Immunology
• Respiratory Medicine
• Allergy Research

Background:

• Asthma is a chronic inflammatory lung condition characterized by T cell-mediated flares.
• The precise identity of long-lived memory T cells driving allergic recall responses remains unclear.

Purpose of the Study:

• To characterize the specific CD4+ T cell population responsible for allergic recall responses in asthma.
• To investigate the role of Interleukin-9 (IL-9) as an effector cytokine in allergic airway inflammation.

Main Methods:

• Utilized a mouse model of chronic allergen exposure followed by a resting period.
• Employed single-cell RNA sequencing (scRNA-seq) and single-cell ATAC sequencing (scATAC-seq).
• Investigated the effects of IL-9 blockade and genetic deletion on airway inflammation and hyperreactivity.

Main Results:

• Identified a CD4+ T cell subpopulation secreting IL-9 with a resident memory T cell phenotype.
• Demonstrated that blocking or deleting IL-9 significantly reduced airway inflammation and hyperreactivity during allergen recall challenges.
• Showcased IL-9 secretion as allergen recall-specific and amplified by IL-33.
• Defined the cellular identity of a distinct proallergic cytokine-producing T cell population using multi-omics approaches.

Conclusions:

• IL-9 secretion by a multicytokine-producing CD4+ T cell population is essential for allergen recall responses in a mouse model of allergic airway inflammation.
• This study defines a key cellular mechanism underlying allergic memory in asthma.
• Targeting IL-9 or these specific T cells may offer novel therapeutic strategies for managing allergic asthma flares.