T lymphocytes develop from a common lymphoid progenitor in the bone marrow that also gives rise to B lymphocytes, but those progeny destined to give rise to T cells leave the bone marrow and migrate to the thymus (see Fig. 7.2). This is the reason they are called thymus-dependent (T) lymphocytes or T cells.
Lymphoid progenitors which have developed from hematopoietic stem cells in the bone marrow migrate to the thymus to complete their antigen-independent maturation into functional T cells . In the thymus, T cells develop their specific T cell markers, including TCR, CD3, CD4 or CD8, and CD2.
T-cells mature in the thymus gland or in the lymph nodes. Since the thymus is only 10-15% functional in the adult, the lymph nodes take on greater importance in the maturation process.
The developing progenitors within the thymus, also known as thymocytes, undergo a series of maturation steps that can be identified based on the expression of different cell surface markers. The majority of cells in the thymus give rise to αβ T cells, however approximately 5% bear the γδ T cell receptor (TCR).
Thymocytes normally mature and exit from the medulla or cortico-medullary junction but medullary migration is not necessarily a prerequisite for emigration.
1) Made productive TCR β chain re-arrangement.2) Signals for proliferation (similar β chain) and maturation.3) Suppresses further β chain re-arrangement (allelic.exclusion)4) Signals for TCR α chain to undergo re-arrangement.4) Induces development to CD4+8+ (double positive) stage.
B cells mature into B lymphocytes in the bone marrow, while T cells migrate to, and mature in, a distinct organ called the thymus. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen and lymph nodes) where they survey for invading pathogens and/or tumor cells.Jan 3, 2021
The requirement for pre-TCR expression results in the arrest of thymocytes at the DN3 stage (β checkpoint), which is uniquely permissive for V-DJβ recombination; only cells expressing pre-TCR survive and develop beyond the DN3 stage.
ProT cells are immature T-cell precursors, which undergo positive and negative selection in the host thymus. Thus, they become restricted to the recipient's major histocompatibility complex (MHC) yielding host tolerant T lymphocytes that bypass the clinical challenges associated with GVHD.
It is thought that, when TCRs bind too strongly to the MHC complexes in the thymus, the intracellular signaling is so strong that it actually leads to cell death, thereby eradicating immature T cell that have a high likelihood of being self-reactive and attacking our own cells.Aug 20, 2018
Why do newly developed T cells decline in number after puberty? T cells mature in the thymus and after puberty the thymus slowly wastes away, leading to the decline of new T cells development.