Which organ is essential for maturation of T lymphocytes?

• A. Bone marrow
• B. Thymus
• C. Spleen
• D. Lymph node

Answer: (B)

T lymphocyte maturation requires the thymus because it provides the specialized environment where developing T cells undergo essential education and selection. Progenitors arrive from the bone marrow and migrate to the thymus, where cortical thymic epithelial cells mediate positive selection to ensure T cells can recognize self-MMC-presented antigens, and medullary thymic epithelial cells drive negative selection to eliminate T cells with strong self-reactivity. This thymic schooling yields mature, naïve T cells that exit to peripheral lymphoid tissues. The spleen and lymph nodes are secondary sites for immune responses, not sites of T cell maturation, while the bone marrow supplies the progenitors but does not complete T cell maturation.