Final answer:
Sustentacular cells, also known as Sertoli cells, create a blood-testis barrier that protects developing sperm cells from substances in the blood and prevents their antigens from causing an immune response.
Step-by-step explanation:
Developing sperm cells are protected by a blood-testis barrier formed by A) Sustentacular cells. These sustentacular cells, also known as Sertoli cells, provide structural and nutritional support to the germ cells during the process of spermatogenesis. Sertoli cells extend from the peripheral basement membrane to the lumen of the seminiferous tubules, enveloping the germ cells. They exhibit tight junctions among themselves, creating a barrier that prevents bloodborne substances from reaching the developing sperm and also stops surface antigens of the sperm from entering the bloodstream and causing an autoimmune response.
Sertoli cells are critical to testicular function as they not only support developing germ cells but also regulate the process of spermatogenesis by secreting signaling molecules. The presence of Leydig cells is crucial as well since they produce testosterone, an essential hormone for male sexual development and reproductive function. However, Leydig cells are not responsible for forming the blood-testis barrier; their main role is related to the production of hormones rather than the protection of germ cells.