IL1RL1 and airway hyperresponsiveness: [23], [34]–[36]. IL1RL1 is located on chromosome 2q12. IL1RL1 translation results in 3 isoforms, of which IL1RL1-a is soluble [37]. The IL1RL1 gene encodes the receptor for interleukine (IL) 33, and is located on mast cells, T helper type 2 (Th2) cells, regulatory T cells, and macrophages [38]–[40]. IL33 stimulates Th2 cytokine responses, such as IL4, IL5 and IL13, that induce eosinophilic influx, airway inflammation, airway hyperresponsiveness, and mucus production [23]. IL1RL1-a may act as a decoy receptor for IL33 thus affecting the inflammatory response to epithelial damage [17].