Background: Interleukin (IL) 13 is a key cytokine in asthma, regulating fibrosis, airway remodeling, induction of immunoglobulin E synthesisby B cells, bronchial hyperresponsiveness, and mucus production. IL-13 signals through the type II IL-4 receptor (IL-4R), which is composed of the IL-4Rα and the IL-13Rα1 chains. Another IL-13 binding chain, IL-13Rα2, binds IL-13 with high affinity but has no known signaling
capability and is thought to serve as a decoy receptor providing tight regulation of IL-13 responses.

Methods: In this study, we investigated the cellular localization of IL-13Rα2 in human primary bronchial epithelial cells and fibroblasts using flow cytometry and confocal microscopy, as well as the in vivo expression of IL-13Rα2 in the human bronchial mucosa by means of immunohistochemistry.

Results: IL-13Rα2 is predominantly an intracellular rather than a membrane-bound molecule in both human primary bronchial epithelial cells and fibroblasts and displays a diffuse granular cytoplasmic distribution in both cell types. IL-13Rα2 protein is expressed in vivo in the human bronchial mucosa with its expression being higher in bronchial epithelial cells than bronchial fibroblasts both in vivo and in vitro.

Conclusions: IL-13Rα2 is expressed by both human primary bronchial epithelial cells and fibroblasts as an intracellular protein with a diffuse cytoplasmic distribution. In vivo, IL-13Rα2 is expressed in the human airway mucosa mainly by bronchial epithelial cells.

Key words: IL-13 receptor α2. Intracellular protein. Cellular localization. Cytoplasmic compartment. Bronchial epithelial cells. Bronchial fibroblasts.