TLR9 and graft versus host disease: Thus, they hypothesize that the lower incidence of GVHD which occurs when UCB is used instead of adult blood is due to the up-regulated expression of immune-regulatory miRNAs (miR-146a and miR-155), resulting in the down regulation of proteins (toll-like receptor 9, myeloid differentiation primary response 88, IL-1 receptor-associated kinase 1, interferon regulatory factor 7) in the toll-like receptor 9 signaling pathway (104).