The OX40/OX40L axis is a central player in promoting TH2 polarization of naïve T-cells in the lymph node, with knockout mouse models of either molecule showing a marked reduction in airway hyperresponsiveness, eosinophilia, and pulmonary inflammation when challenged with ovalbumin [34, 35]. The gene discussed is TNFSF4; the disease is airway hyperresponsiveness.