In both asthmatic and normal airway mucosa, the main cells are T lymphocytes; these are activated in response to antigen stimulation or during acute asthma exacerbations and produce large amounts of cytokines, such as Interleukin (IL-)3, IL-4, IL-5 or granulocyte-macrophage colony-stimulating factor (GM-CSF), which are significantly upregulated after antigen provocation, and their receptors have been identified locally on the surface of inflammatory cells [14]. The gene discussed is CSF2; the disease is asthma.