The Thymic Niche and Thymopoiesis


The thymus, a bilobate gland located in the upper anterior thorax in higher vertebrates, is the major site of T‐lymphocyte production. This primary lymphoid organ composed of various nonlymphoid elements, referred to as the thymic stroma, governs the maturation and tolerance induction of haematopoietic precursors into immune‐competent nonautoreactive T cells. Whilst naturally involuting with age, the thymic stromal compartment remains dynamic in nature throughout life and retains the potential to regenerate.

Keywords: thymocyte; T lymphocyte; T‐cell receptor; differentiation; thymus

Figure 1.

Ultrastructure of the thymus. The thymic lobes are surrounded by the capsule (CAP) and are separated into a thymocyte‐rich cortex (C) and an epithelial cell‐rich medulla (M), separated by the corticomedullary junction (CMJ). The vasculature is mainly found in the medulla with its characteristic perivascular space (PVS).

Figure 2.

Overview of thymopoiesis. The precursors enter the thymus and then differentiate into distinct competent T‐cell populations. This process involves the sequential transition through various stages of maturation and intimate interaction with particular stromal elements composing the thymus. C, cortex; CAP, capsule; CLP, common lymphoid precursor, CMJ, corticomedullary junction; EDP, early double‐positive; ISP, immature single‐positive; L, lobule; LDP, late double‐positive; M, medulla; MHC, major histocompatibility complex; S, septae (trabeculae); SC, subcapsule; SMSP, semi‐mature single‐positive; T, T cell; TCR, T‐cell receptor. T‐cell differentiation pathway adapted from Boyd R and Hugo P (1991). Towards an integrated view of thymopoiesis. Immunology Today12: 71–79, with permission from Elsevier Science; the thymus ultrastructure was inspired from Van Ewijk W (1988) Cell surface topography of thymic microenvironments. Laboratory Investigation59: 579–590.



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Further Reading

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Hollander G, Gill J, Zuklys S et al. (2006) Cellular and molecular events during early thymus development. Immunological Reviews 209: 28–46.

Janeway CA, Travers P, Walport M and Capra JD (eds) (1999) The thymus and the development of T lymphocytes. In: Immunobiology. The Immune System in Health and Disease, 4th edn, pp. 227–260. New York: Elsevier.

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Chidgey, Ann, Boyd, Richard, and Hugo, Patrice(Sep 2007) The Thymic Niche and Thymopoiesis. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000526.pub2]