AITRL protein , also known as TNFSF18 or Osteostat, is detectable in human microvascular EC and is highly up-regulated by IFN-alpha and IFN-beta.
AITRL inhibits differentiation of osteoclasts from monocytic precursor cells. It also suppresses the early stage of osteoclastogenesis via inhibition of macrophage colony-stimulating factorinduced receptor activator of NF-kappaB (RANK) expression in the osteoclast precursor cells. It does not inhibit lipopolysaccharide-induced RANK expression in monocytes and dendritic cells, or activation-induced RANK expression in T cells. AITRL is a novel regulator of osteoclast generation and substantiate the major role played by the endothelium in bone physiology.