Further, we assessed miRNA expression and their functions only in pBECs with or without infection, whereas co-culturing epithelial cells with relevant cells, e.g. neutrophils or macrophages which are also a source of MMP-9 in asthmatics [48], may affect miRNA expression and/or their targets in epithelial cells due to cell to cell crosstalk. The gene discussed is MMP9; the disease is infection.