Which of the following is the primary site for T-lymphocyte differentiation?

Correct option is D

The thymus is a lymphoid organ located in the mediastinum and is the central site for T-lymphocyte (T-cell) maturation and differentiation. Immature T-cells from the bone marrow migrate to the thymus where they undergo selection processes to ensure immunocompetency. The thymus is most active during childhood and regresses in adulthood.
Explanation of options: (a) ✘ Thalamus – A brain structure involved in relaying sensory information, not related to immune cell development. (b) ✘ Epithalamus – A part of the brain containing the pineal gland, which regulates circadian rhythms. (c) ✘ Hypothalamus – Regulates autonomic functions and hormones but not T-cell differentiation. (d) ✔ Thymus – Essential for the differentiation and maturation of T-lymphocytes.