Furthermore, several studies regarding Fms-like tyrosine kinase 3 ligand (Flt3-L), which can reverse allergen-induced mouse models of asthma, demonstrated that Flt3-L not only increases the number of CD4+CD25+FOXP3+IL-10+ICOS+ Tregs but also recruits more CD11chighCD11blow DCs to the lung of OVA-sensitized mice, both of which worked synergistically to attenuate AHR through the reinforced interaction between ICOS and ICOSL (124, 125). Here, ICOS is linked to asthma.