Where do T cells develop and mature?

• A. Thymus
• B. Red bone marrow
• C. Spleen
• D. Lymph nodes

Answer: (A)

The thymus is the specialized environment where T cells complete their maturation. Although their precursors originate in the red bone marrow, they migrate to the thymus to finish development. Inside, thymocytes rearrange their T-cell receptor genes, then undergo selection—positive selection in the cortex ensures they can recognize self-MHC, and negative selection in the medulla eliminates those that strongly react to self-antigens. Successfully matured T cells then exit to the periphery to populate secondary lymphoid tissues and respond to antigens. Red bone marrow mainly provides the initial lymphoid progenitors, while the spleen and lymph nodes are sites of immune activation, not maturation, for T cells.