TROY (also known as TAJ and TNFRSF19) is a 45‑55 kDa member of the TNF receptor superfamily of molecules (1‑4). It is widely expressed in the embryo, but shows limited expression in adult. In particular, embryonic TROY is found in embryonic epithelium, neural tube, and mesenchyme, and developing neurons of the hippocampus and thalamus (5, 6). In the adult, TROY is found in the nervous system associated with dorsal root and retinal ganglia neurons, astrocytes, and microglia, and in hair follicles where it is expressed by dermal papilla matrix cells (4, 7, 8, 9). In human, TROY has also been found on melanoma cells, not normal melanocytes (10).  TROY is reportedly a component of the Nogo-A receptor, taking the place of p75 in a membrane-bound LINGO-1:NgR1: TROY complex (6, 8, 9). This complex purportedly mediates axon repulsion initiated by one of five myelin-associated inhibitory factors (OMpg; CD100; Ephrin B3; Nogo-A; MAG) (6, 11). In the hair follicle, TROY binds LTa and acts with Eda to drive secondary hair follicle development (4, 12). Mature human TROY is a 394 amino acid (aa) type I transmembrane protein (1-3). It possesses a 141 aa extracellular region (aa 30-170) that contains three 40 aa TNFR cysteine motifs, and an extended 232 aa cytoplasmic domain (aa 192-423). There is one potential isoform that shows a two aa substitution for aa 416-423. The extracellular domains of human and mouse TROY share 90% aa identity.