In addition, NGF-mediated TLR9 upregulation might be in line with the observation that synthetic immunostimulatory sequence (CpG motif ligands) activates TLR9, resulting in a more effective response than steroids in attenuating both asthma, allergic conjunctivitis and allergic rhinitis via specific Th2 downregulation [5,39,40]. Here, NGF is linked to atopic conjunctivitis.