T cells mature in which organ?

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

Answer: (A)

T cells finish their development in the thymus, a primary lymphoid organ where precursor cells migrate from the bone marrow to complete maturation. In the thymus they undergo T-cell receptor gene rearrangement and undergo selection so that they recognize self-MHC molecules but do not react strongly to self-antigens. This thymic education ensures they become functional, self-tolerant T cells before entering the bloodstream and later encountering antigens.

The bone marrow is where hematopoietic stem cells reside and where B cells mature, while the spleen and lymph nodes are secondary lymphoid organs where mature lymphocytes respond to antigens. Those sites host immune responses rather than the final stages of T cell maturation.