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The development of T lymphocytes
Dr. Glorivee Rosario Pérez
BIOL 4056
Parham P. (2009). The Immune System. Third Edition. Garland Publishing, New York.
The development of T cells in the thymus
T lymphocytes
Figure 7-2
T lymphocytes cont.
T cells lineages (develop in the thymus):
α:β T cells (majority)
γ:δ T cells (minority)
CD4
CD8
Thymus:
Is a lymphoid organ in the upper anterior thorax just above the heart.
It contains immature T cells (thymocytes), which are embedded in a network of epithelial cells (thymic stroma). These elements form:
Cortex
Medulla
The cellular organization of the thymus
Figure 7-8
Thymus development:
Birth – the human thymus is fully developed.
Puberty – increase in size.
Adult (30 years) – degeneration of the thymus.
B vs T cells
The bone marrow is continually turning over the B cell repertoire during the whole of person’s lifetime.
The thymus works principally during youth, when it serves to accumulate a repertoire of T cells that can then be used throughout life.
Two lineage of T cells:α:β and γ:δ
Maturation of thymocytes into mature T cell occurs in distinct stages. These are marked by changes in the status of the:
T-cell receptor gene.
expression of the T-cell receptor protein.
production of other T-cell surface glycoprotein: CD4, CD8 and CD3 complex.
Two lineage of T cells:α:β and γ:δ cont.
Progenitor Cells(no cell-surface glycoproteins)
Thymic stromal cells(epithelial cells)
Subcapsular region of the outer cortex
Progenitor Cells(Proliferate)
A week
T-cell express specific adhesion molecule : CD2No expression of : TCR complex, CD4, CD8, CD3
(double negative thymocytes: CD4-CD8-)
Two lineage of T cells:α:β and γ:δ cont.
Figure 7-24
Figure 7-25
Cells that fail to make productive
rearrangement die by apoptosis and are
phagocytosed by macrophages in the thymic cortex.
Two lineage of T cells:α:β and γ:δ cont.
Expression of CD4 and CD8
TCR α-chain genes
Positive and negative selection of the T-cell
repertoire
Positive selection : MHC
Is a process in the thymus that selects immature T cells with receptors that
recognize peptide antigens presented by self-MHC molecules.
Only cells that are positively selected are allowed to continue their maturation.
Positive selection : MHC cont.
Positive selection
takes place in the
cortex of the thymus.
Positive selection : CD4 and CD8 co-receptor
Single-positive thymocytes – double positive thymocytes mature into cells that express just one or other of the two co-receptors.
CD4+CD8+
CD4+CD8-
CD4-CD8+
Positive selection : CD4 and CD8 co-receptor cont.
α-chain genes
Negative selection
Process in the thymus whereby developing T cells that recognize self antigens are induced to
die by apoptosis.
Negative selection cont.
Mature T-cell
Thymus → secondary lymphoid tissue
Mature naïve T cell↓
Thymus ↓
Blood↓
Secondary lymphoid tissues
↓Lymph
↓Blood
Thymus → secondary lymphoid tissue cont.
Naïve T cells are activated by their specific antigens in T cell rich areas of secondary lymphoid tissues
↓Final phases of T cell development and
differentiation↓
The mature T cell divide and differentiate into effector T cells
CD8 T cells CD4 T cells (TH1/TH2)
↓Some stay in the lymphoid tissues while others
migrate to sites of infection
Additional information about T-cell
Bone marrow transplantation
Bone marrow transplantation cont.
Disease
Summary
Summary
Summary cont.
Summary cont.
Summary cont.
Summary cont.