Which primary lymphoid organ is responsible for the maturation of T cells?

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

Answer: (B)

T cells undergo their maturation in the thymus, a primary lymphoid organ where they develop from precursors that migrate there from the bone marrow. In the thymus, these cells undergo T cell receptor gene rearrangement and undergo critical education: positive selection in the cortex ensures they can recognize self-MHC, and negative selection in the medulla eliminates cells that react too strongly to self-antigens. This process produces a self-tolerant, functional T cell repertoire. The bone marrow is where the earliest lymphoid precursors arise and where B cells mature, while the spleen and lymph nodes are secondary lymphoid tissues where mature lymphocytes encounter antigens. Therefore, the thymus is the site responsible for T cell maturation.