In fact, transforming growth factor-β must be present along with transforming growth factor-α to stimulate proliferation of fibroblasts.13 Homma et al. 22 found that exposure or colonisation by Staphylococcus aureus in the airway may enhance the remodelling of tissue through a transforming growth factor-α-dependent induction of matrix metalloproteinase-1 expression and may, thereby, promote remodelling in airway diseases in which Staphylococcus aureus is implicated, such as asthma and chronic rhinosinusitis with nasal polyps. The gene discussed is MMP1; the disease is asthma.