- Sputum levels of metalloproteinase-9 and tissue inhibitor of metalloproteinase-1, and their ratio correlate with airway obstruction in lung transplant recipients: relation to tumor necrosis factor-alpha and interleukin-10. Beeh, K.M., Beier, J., Kornmann, O., Micke, P., Buhl, R. J. Heart Lung Transplant. (2001)