Discovered in 1859 by Franz Leydig, an anatomist from Germany, Leydig cells are found in the testicles next to the seminiferous tubules, where sperm is produced within the testes. Also known as interstitial cells of Leydig, these cells lie between other structures of the testicles and help support these other structures and cells. They play a vital role in maintaining proper levels of male hormones, including testosterone.
When Leydig cells are exposed to Luteneizing Hormone (LH), which is secreted by the pituitary gland, they produce androgens, or male hormones, including testosterone, the hormone that determines male characteristics in mammals and regulates male reproductive function. Malfunctions in these cells are believed to be the cause of some forms of infertility. The sensitivity of these cells to LH is increased by exposure to follicle stimulating hormone (FSH), which causes them to produce more LH receptors.
Inside the Leydig cells of human males can be found Reinke's crystals, small rod-shaped crystals made of protein. The purpose of these crystals is uncertain, but they occur only in humans and seem to occur in larger quantities in older men, leading some to believe that they are a byproduct of a degenerative process related to aging. They appear to have no contribution to androgen or testosterone production, and they can be used to identify Leydig cells easily when viewing testicular tissue under a microscope.
Occasionally, a Leydig cell tumour develops within the testicles. These types of tumours are very rare and usually are benign, though they can result in excessive testosterone production. They occur most often in young men, and a common symptom is the occurrence of exaggerated masculine characteristics. On rare occasions when this type of tumour presents in females, symptoms include masculinization, or the occurrence of secondary male sex characteristics in a female patient.
A Sertoli-Leydig cell tumour involves Leydig cells as well as Sertoli cells, supportive cells that play a vital role in the growth of sperm cells within the testicles. Symptoms are similar to those of regular Leydig tumours, but about one-quarter of Sertoli-Leydig cell tumours are malignant. Treatment usually involves surgery to remove the tumour, with care taken to preserve the patient's fertility when possible, though malignant tumours are treated more aggressively and might involve removing the testicle and subsequent radiation treatment. Prognosis is good in most cases, because the tumours tend to grow more slowly than many other malignant growths.