MMP9 and allergic disease: Research in established allergic disease have revealed association between e.g. plasma chemokine ligand 5 (CCL5) and persistent asthma between 4 and 16 years of age [9] and upregulation of markers of inflammation such as myeloperoxidase (MPO), matrix metalloproteinase-9 (MMP9) and CCL22 in children with atopic dermatitis compared to healthy controls [10].