IL-9 is required for multi-cytokine producing tissue-resident memory CD4+ T cell-dependent allergic airway recall responses

Asthma is a chronic inflammatory lung disease with intermittent flares predominately mediated through memory T cells. Yet, the identity of long-term memory cells that mediate allergic recall responses are not well defined. In this report, using a mouse model of chronic allergen exposure followed by an allergen-free rest period, we have characterized a sub-population of Th2 cells that secretes IL-9 as an obligate effector cytokine. IL-9-secreting cells have a resident memory T cell phenotype and blocking IL-9 during a recall challenge significantly diminishes airway inflammation and airway hyperreactivity. T cells secrete IL-9 in response to allergen recall and secretion is amplified by IL-33. Using scRNA-seq and scATAC-seq, we define the cellular identity of a distinct populations of T cells with pro-allergic cytokine patterns. Thus, in a recall model of allergic airway inflammation, IL-9 secretion from a multi-cytokine producing cell population is required for an allergen recall response. Overall design: 1. To compare transcriptional profile of ST2+CD4 T cells and ST2- CD4 T cells in the lung, ST2+ and ST2- CD4 T cells were isolated from the lung in a recall model and pooled together to generate replicates of ST2+ CD4 T cells and ST2- CD4 T cells, with a total of 4 samples for scRNA-seq and snATAC-seq analysis. 2. To examine to the function of IL-9 in allergic recall response, single suspension of total viable cells from the lung were generated from the mice that were treated with anti-IL-9 or isotype (100 µg/ml) during the recall challenge. For this experiment three replicates of total lung cells after anti-IL-9 or isotype treatment were used for scRNA-seq analysis.