TLR9 and asthma: Bacterial products also exert immunoregulatory effects on asthma development, and it was postulated that the possible mechanism underlying the immunoregulatory effects of bacterial compounds is via recruitment of regulatory T (Treg) cells to the airways and the activation of mucosal dendritic cells (DCs) by TLRs-dependent signaling, especially through TLR2/6 and TLR9 (17, 21).