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thymus cell differentiation 701 thymus-dependent (TD) antigen
subjects with immunodeficiencies involving T cell function.
Differentiation is associated with surface markers, the presence
or disappearance of which characterizes the different
stages of cell differentiation. Proliferation of the subcapsular
thymocytes is extensive. Most of these cells die, but the
remaining cells continue to differentiate, become smaller,
and move through interstices in the thymic medulla. Fully
developed thymocytes pass through the walls of the postcapillary
venules to reach the systemic circulation and seed
in the peripheral lymphoid organs. Some recirculate, but do
not return to the thymus.
thymus cell differentiation
Stem cell maturation and differentiation into mature T lymphocytes
in the thymus are accompanied by the appearance
and disappearance of specific surface CD antigens. In
humans, the differentiation of CD38 + stem cells into early
thymocytes is signaled by the appearance of CD2 and CD7,
followed by the transferrin receptor marker; expression of
IL-2
IL-4
Pluripotent
stem cell
Cortical
epithelial cell
UEA-1+ medullary
epithelial cell
Cortex
Positive selection—restriction
Medulla
Negative selection—tolerance
Dendritic
cell
Dendritic
cell
A model for thymic compartment specialization.
T LYMPHOCYTE LINEAGE
IL-1
IL-6
Prothymocyte
Antigen driven
?
Periphery
Activation—effector function
CD1 identifying thymocytes in the mid-stage of differentiation
when T cell receptor genes γ and δ and later α and β
rearrange; and expression of CD3, CD4, and CD8 surface
antigens by thymocytes. CD1 usually disappears at this
time. Ultimately, the CD4 +/ CD8 + and CD4 –/ CD8 + subpopulations
that both express the CD3 pan-T cell marker appear.
An analogous maturation of T cells takes place in mice.
thymus cell education
Thymus cell differentiation.
thymus-dependent (TD) antigen
An immunogen that requires antigen-specific T lymphocyte
cooperation for B cells to synthesize specific antibodies.
The immunogen binds to the receptors of B cells to
induce activation but is unable to induce B cell differentiation
or immunoglobulin production without direct
intercellular contact with a primed helper T cell. T cell
cooperation is required for B cells to synthesize specific
antibodies. Presentation of thymus-dependent antigen to
Lymphoid
stem cell
T Lymphoblast T Cell
Differentiation of a stem cell into a mature T cell.
IL-1
IL-2
IL-6
IL-7
(ymus)
T