Leydig Cells (LC) are located in the interstitium of the testis near the seminiferous tubules. One of the main functions of LC is to produce testosterone after stimulation by pituitary luteinizing hormone. LC, through synthesis of testosterone, play a key role in mammalian sex determination by inducing differentiation of the Wolffian ducts into male reproductive organs. Additionally, LC produce insulin-like growth factor 3 which is required for scrotal descent of the testis. Recent studies have indicated that molecules such as cyclic nucleotide phosphodiesterases can modulate testosterone production in LC, suggesting that testosterone synthesis may be manipulated using pharmacological targeting. Cultured Human LC are a useful in vitro model to better understand testicular development and to develop treatments for male reproductive disorders. HLC from ScienCell Research Laboratories are isolated from human testis. HLC are cryopreserved at passage one and delivered frozen. Each vial contains >5 x 105 cells in 1 ml volume. HLC are characterized by immunofluorescence with antibody specific to GATA-4 and CK-18. HLC are negative for HIV-1, HBV, HCV, mycoplasma, bacteria, yeast and fungi. HLC are guaranteed to further culture under the conditions provided by ScienCell Research Laboratories; however, HLC are not recommended for expanding or long-term cultures due to limited expansion capacity. Recommended Medium It is recommended to use Leydig Cell Medium (LCM, Cat. #4511) for the culturing of HLC in vitro.