Question: Sperm count in human males is influenced by a variety of factors. One of the most important variables affecting sperm count is the number of Sertoli cells located in seminiferous tubules of the testes. The Sertoli cells' primary function is to nurture cells through the process of spermatogenesis by providing them with nutrients and an environment conducive to spermatogenesis. Each Sertoli cell has a set number of spermatozoa that it can support. Sertoli cells have an additional role in forming the blood-testis barrier that provides immune privilege for the seminiferous tubules. This forms a physical barricade that keeps the developing sperm from coming into contact with cells of the immune system.
While it is not clear as to all the factors involved in determining Sertoli cell number, it is apparent that their development is most critical during the first nine months of life and prior to puberty. Events that affect the development of Sertoli cells in young males can influence fertility later in life. There may also be genetic factors involved in determining the number of Sertoli cells formed in a particular male.
The following data were collected from two groups of men. The men in group 1 had a normal sperm count while the men in group 2 were seeking infertility treatment due to a low sperm count. Levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary were measured as were the testicular hormones inhibin-B and testosterone in an attempt to determine which hormones seem to be linked to reduced sperm count.
\begin{tabular}{ccccc}
\hline Sample Group & LH & FSH & Inhibin-B & Testosterone \\
\hline 1 & $5.3 \mathrm{IU} / \mathrm{L}$ & $5.0 \mathrm{IU} / \mathrm{L}$ & $190 \mathrm{pg} / \mathrm{mL}$ & $18.0 \mathrm{nmol} / \mathrm{L}$ \\
2 & $3.1 \mathrm{IU} / \mathrm{L}$ & $17.6 \mathrm{IU} / \mathrm{L}$ & $51 \mathrm{pg} / \mathrm{mL}$ & $17.8 \mathrm{nmol} / \mathrm{L}$ \\
\hline
\end{tabular}
Why would it be important for the Sertoli cells to establish a blood-testis barrier and immune privilege?

Options:
A. to prevent the immune cells from attacking the sperm cells, which display different antigens from the other cells in the body
B. to prevent the developing sperm cells from leaving the reproductive system
C. to prevent blood from flowing into the testes
D. to keep the developing sperm cells from entering into the epididymis before they are mature
Answer: The blood-testis barrier is described in the passage as a barricade to establish immune privilege for the testes. To answer this question, you need to think about how the sperm cells in the testes would compare to other cells in the body. Sperm cells are haploid, and all are genetically different from each other and from other cells in the body. Because they are genetically different, they should express unique surface antigens. If the cells of the immune system were to contact the sperm, they would be perceived as foreign and could be subject to immune system attack, which would destroy the sperm. For this reason, the blood-testis barrier is required to keep the sperm away from the immune cells. The remaining choices do not make good sense. Sperm cells will eventually leave the reproductive system during ejaculation. It also would not make sense to indicate that the blood flow to the testes needs to be cut off. This would prevent oxygen and nutrient flow to the area. Preventing the sperm from moving to the epididymis before they are ready does not provide an explanation for why the sperm cells need to be kept separate from the cells of the immune system. The correct answer is A.