SHH and allergic asthma: Many studies using mouse models, human tissues and genome-wide association (GWAS) have indicated that the Sonic Hedgehog (Shh) and Hedgehog (Hh) signaling pathways are involved in allergic asthma (2–8), and Hh signaling to naïve CD4+ T-cells promotes Th2 differentiation in vitro in mouse and human (4, 9, 10).