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Which lymphatic organs are the main sites of B-cell and T-cell maturation in humans?

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Diagram of the human lymphatic system highlighting lymphatic vessels and major lymphoid organs, including lymph nodes, adenoids, tonsils, thymus gland, spleen, appendix, bone marrow, and ducts. — lymphatic system The human lymphatic system, showing the lymphatic vessels and lymphoid organs.

In humans, the primary lymphoid organs responsible for the maturation of lymphocytes are the bone marrow and the thymus.1

While all lymphocytes originate from stem cells in the bone marrow, the maturation process differs by cell type:

B cells: These lymphocytes remain in the bone marrow to undergo maturation. Although the fetal liver serves as a site for B-cell differentiation during prenatal development, the bone marrow is the primary organ for this process in humans.12
T cells: Prospective T cells migrate from the bone marrow to the thymus, where they undergo further growth and differentiation.13

Once mature, these cells exit the primary lymphoid organs and travel through the bloodstream to secondary lymphoid organs, where they are activated by antigens.1