Regulation of the testis.

The testicular cells are regulated by factors produced locally in the testis. These factors include peptide growth factors, pro-opiomelanocortin derivatives, neuropeptides and steroids. Several agents able to affect steroido- and spermatogenesis can also affect leukocytes and many of the testis-regulating factors are produced by immune cells, suggesting that testicular cells and leukocytes may interact. In the present article, the effects of various testicular cell and leukocyte produced factors on steroido- and spermatogenesis are reviewed. The possibility that leukocytes may produce substances able to affect the testicular functions suggests that inhibition of immune system activation in the testis may be important also for reasons other than protection of autoantigenic germ cells from an autoimmune attack.