MMP9 and inflammatory response: Pinheiro et al. (2015) demonstrated that VAChT deficiency-induced airway inflammation with increased levels of TNF-α and IL-4. Mice with decreased levels of VAChT showed increased deposition of collagen fibers and elastic fibers in their airway walls, consistent with an increase in MMP-9 and TIMP-1 positive inflammatory cells. The evaluation of lung function in vivo showed hyperactivity of the airways to methacholine in VAChT-deficient mice; the authors concluded that an intact cholinergic pathway is necessary for maintaining the homeostasis of the lung (Pinheiro et al., 2015).