To cite this article: Alkhouri H, Hollins F, Moir LM, Brightling CE, Armour CL, Hughes JM. Human lung mast cells modulate the functions of airway smooth muscle cells in asthma. Allergy 2011; 66: 1231–1241. Background:  Activated mast cell densities are increased on the airway smooth muscle in asthma where they may modulate muscle functions and thus contribute to airway inflammation, remodelling and airflow obstruction. Objectives:  To determine the effects of human lung mast cells on the secretory and proliferative functions of airway smooth muscle cells from donors with and without asthma. Methods:  Freshly isolated human lung mast cells were stimulated with IgE/anti‐IgE. Culture supernatants were collected after 2 and 24 h and the mast cells lysed. The supernatants/lysates were added to serum‐deprived, subconfluent airway smooth muscle cells for up to 48 h. Released chemokines and extracellular matrix were measured by ELISA, proliferation was quantified by 3H‐thymidine incorporation and cell counting, and intracellular signalling by phospho‐arrays. Results:  Mast cell 2‐h supernatants reduced CCL11 and increased CXCL8 and fibronectin production from both asthmatic and nonasthmatic muscle cells. Leupeptin reversed these effects. Mast cell 24‐h supernatants and lysates reduced CCL11 release from both muscle cell types but increased CXCL8 release by nonasthmatic cells. The 24‐h supernatants also reduced asthmatic, but not nonasthmatic, muscle cell DNA synthesis and asthmatic cell numbers over 5 days through inhibiting extracellular signal‐regulated kinase (ERK) and phosphatidylinositol (PI3)‐kinase pathways. However, prostaglandins, thromboxanes, IL‐4 and IL‐13 were not involved in reducing the proliferation. Conclusions:  Mast cell proteases and newly synthesized products differentially modulated the secretory and proliferative functions of airway smooth muscle cells from donors with and without asthma. Thus, mast cells may modulate their own recruitment and airway smooth muscle functions locally in asthma.