PTPN1 and chronic obstructive pulmonary disease: Under normal conditions, PTP1B suppresses S100A9 expression during an RSV infection, while an enhanced secretion of S100A9 with resulting inflammation was seen in wild-type mice exposed to cigarette smoke as a result of a desensitized PTP1B activity, as well as in differentiated human bronchial epithelial cells from COPD donors after an RSV infection [39].