The development of t lymphocytes
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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.
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The development of T cells in the thymus
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T lymphocytes
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Figure 7-2
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T lymphocytes cont.
T cells lineages (develop in the thymus):
α:β T cells (majority)
γ:δ T cells (minority)
CD4
CD8
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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
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The cellular organization of the thymus
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Figure 7-8
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Thymus development:
Birth – the human thymus is fully developed.
Puberty – increase in size.
Adult (30 years) – degeneration of the thymus.
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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.
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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.
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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-)
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Two lineage of T cells:α:β and γ:δ cont.
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Figure 7-24
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Figure 7-25
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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.
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Expression of CD4 and CD8
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TCR α-chain genes
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Positive and negative selection of the T-cell
repertoire
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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.
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Positive selection : MHC cont.
Positive selection
takes place in the
cortex of the thymus.
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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+
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Positive selection : CD4 and CD8 co-receptor cont.
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α-chain genes
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Negative selection
Process in the thymus whereby developing T cells that recognize self antigens are induced to
die by apoptosis.
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Negative selection cont.
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Mature T-cell
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Thymus → secondary lymphoid tissue
Mature naïve T cell↓
Thymus ↓
Blood↓
Secondary lymphoid tissues
↓Lymph
↓Blood
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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
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Additional information about T-cell
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Bone marrow transplantation
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Bone marrow transplantation cont.
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Disease
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Summary
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Summary
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Summary cont.
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Summary cont.
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Summary cont.
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Summary cont.