SHH and allergic asthma: Given the functional relationship between Foxa2 and Shh, the opposing roles of Shh and Foxa2 in allergic asthma, the role of Hh in driving Th2 differentiation, and the importance of CD4+ Th2 responses in amplifying asthma, we investigated the function of Foxa2 in CD4 T-cells in AAD.