Leydig cells

Examples of Leydig cells in the following topics:

• Hormonal Regulation of the Male Reproductive System

  • However, it is known that initiation of spermatogenesis occurs at puberty due to the interaction of the hypothalamus, pituitary gland, and Leydig cells.
  • The Leydig cells are also capable of producing estradiol in addition to their main product, testosterone.
  • In the testes, LH binds to receptors on Leydig cells, which stimulates the synthesis and secretion of testosterone.
  • Testosterone is made in the interstitial cells of the testes.
  • Inhibin is secreted by the Sertoli cells and acts to decrease the levels of FSH.

• Testicular Cancer

  • Although testicular cancer can be derived from any cell type found in the testicles, more than 95% of testicular cancers are germ cell tumors .
  • Most of the remaining 5% are sex cord-gonadal stromal tumors derived from Leydig cells or Sertoli cells.
  • Most testicular germ cell tumors have too many chromosomes, and most often they are triploid to tetraploid.
  • About half of germ cell tumors of the testis are seminomas.

• Testes

  • These are lined with a layer of germ cells that develop into sperm cells (also known as spermatozoa or male gametes) from puberty into old age.
  • The developing sperm travels through the seminiferous tubules to the rete testis located in the mediastinum testis, to the efferent ducts, and then to the epididymis where newly-created sperm cells mature.
  • Leydig cells located between seminiferous tubules produce and secrete testosterone and other androgens important for sexual development and puberty, including secondary sexual characteristics such as facial hair and sexual behavior.
  • The sertoli cells are the testes’ somatic cells, necessary for testis development and spermatogenesis.

• Male and Female Gonads

  • Progesterone and estrogen are secreted by granulosal cells, whereas testosterone is produced by thecal cells.
  • Prior to ovulation, follicle-stimulating hormone is secreted by the granulosal cells that convert testosterone into estradiol.
  • Testosterone is secreted by Leydig cells, which are located between the seminiferous tubules.

• Aging and the Endocrine System

  • This decrease in responsiveness can be attributed to a decrease in IGF-I signaling pathways with advanced cell age.
  • Testosterone is a steroid hormone secreted by the Leydig cells.
  • Estradiol is the female equivalent of testosterone and is secreted from granulosa cells.
  • In vitro, cells treated with testosterone demonstrated a decrease in Ab release.
  • Estrogen acts on the nucleus of the cell by binding with the nuclear endoplasmic reticulum (ER).

• Puberty

  • LH stimulates the Leydig cells of the testes to make testosterone and blood levels begin to rise.
  • For females, as the amplitude of LH pulses increases, the theca cells of the ovaries begin to produce testosterone and smaller amounts of progesterone.
  • Much of the testosterone moves into nearby cells called granulosa cells.
  • Smaller increases of FSH induce an increase in the aromatase activity of these granulosa cells, which converts most of the testosterone to estradiol for secretion into the circulation.

• Specific T-Cell Roles

  • T helper cells assist the maturation of B cells and memory B cells while activating cytotoxic T cells and macrophages.
  • Differentiation into helper T cell subtypes occurs during clonal selection following T cell activation of naive T cells.
  • Cytotoxic T cells (TC cells, or CTLs) destroy virus-infected cells and tumor cells, and cause much of the damage in in transplant rejection and autoimmune diseases.
  • Memory T cells comprise two subtypes: central memory T cells (TCM cells) and effector memory T cells (TEM cells), which have different properties and release different cytokines.
  • Regulatory T cells (Treg cells), also known as suppressor T cells, are crucial for the maintenance of immunological tolerance.

• Natural Killer Cells

  • The role of NK cells is similar to that of cytotoxic T cells in the adaptive immune response.
  • NK cells provide rapid responses to virus-infected cells and respond to tumor formation by destroying abnormal and infected cells.
  • NK cells use wo cytolytic granule-mediated apoptosis to destroy abnormal and infected cells.
  • Virus-infected cells destroyed by cell lysis release their replicated virus particles into the body, which infects other cells.
  • Cells that are osponized with antibodies are easier for NK cells to detect and destroy.

• Lymphoid Cells

  • The three major types of lymphocyte are T cells, B cells, and natural killer cells.
  • If cancer cells evade NK cell detection for long enough, however, they can grow into tumors that are more resistant to NK cell activity.
  • T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humoral immunity.
  • There are two types of T cells involved in adaptive, cell-mediated immunity.
  • Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered in the form of memory cells.

• Maturation of T Cells

  • T cells belong to a group of white blood cells known as lymphocytes and play a central role in the cell-mediated branch of the adaptive immune system.
  • They are distinguished from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T cell receptor (TCR) on the cell surface.
  • T cells can be either helper T cells or cytoxic T cells based on whether they express CD4 (helper) or CD8 (cytotoxic) glycoprotein.
  • A T cell is then signaled by the thymus to become a CD4+ cell by reducing expression of its CD8 cell surface receptors.
  • The remaining cells exit the thymus as mature naive T cells.