The Th2 cytokine Interleukin-13 (IL-13) plays a critical role in allergen-induced airway hyper-responsiveness (AHR). Two different receptors exist for IL-13, designated IL-13Ra1 and 2. IL-13Ra1 exists as a heterodimer of IL-13Ra1 and IL-4Ra as a signaling subunit, whereas IL-13Ra2 acts as a decoy receptor for IL-13. Furthermore, TNFa or IL-4 stimulation induces IL-13Ra2 upregulation, while IL-13Ra1 is constitutively expressed. Cell surface localization of IL-13Ra2 abrogates IL-13 signaling, thus IL-13 induced translocation of the receptor from the cytoplasm provides a mechanism for negative-feedback of IL-13 signaling. IL-13Ra1 expression is predominant in B cells, monocytes and
T cells, whereas IL-13Ra2 expression is highest in glioma cells.
