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thymopentin (TP-5) 698 thymus
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Thymopoietin
Thymopentin
Arg Lys Asp Val Tyr
thymopentin (TP-5)
A synthetic pentapeptide, Arg–Lys–Asp–Val–Tyr, that corresponds
to amino acid residues 32 through 36 of the thymopoietin
thymic hormone. Thymopentin is the minimal
fragment that can produce the biological activities of thymopoietin,
i.e., thymopentin is the active site of thymopoietin.
The cell-mediated immune response is a host defense
mediated by antigen-specific T lymphocytes with nonspecific
cells of the immune system. It offers protection against
intracellular bacteria, viruses, and neoplasms and mediates
graft rejection. It may be transferred passively with primed
T lymphocytes.
thymopoietin
A 49-amino acid polypeptide thymic hormone secreted
by epithelial cells in the thymus. It affects neuromuscular
transmission and immune regulation and also induces
early T lymphocyte differentiation. Thymopentin functions
biologically to normalize immune imbalances related
to hypo- or hyper-responsiveness that may be related to
thymic involution arising from age, thymectomy, or other
factors. It is a 7-kDa protein that facilitates the expression
of Thy-1 antigen on T lymphocytes that may interfere with
neuromuscular transmission, an effect noted in patients
with myasthenia gravis who often develop thymoma.
thymosin
A 12-kDa protein hormone produced by the thymus gland
that may provide T lymphocyte immune function in
thymectomized animals.
36
Structure of thymopoietin and thymopentin.
CH 3 C
H
O
N
1
SER
2
ASP
3
ALA
14
LYS
15
ASP
16
LEU
49
4
ALA
13
THR
17
LYS
5
VAL
12
THR
18
GLU
thymosin -1 (thymopoietin)
A hormone produced by the thymus that stimulates T lymphocyte
helper activity. It induces production of lymphokines
such as interferon and macrophage-inhibiting factor
and enhances Thy-1.2 and Lyt-1, -2, -3 antigens of T lymphocytes.
It may also alter thymocyte terminal deoxynucleotidyl-transferase
(TdT) concentrations.
thymotaxin
Refer to β 2 microglobulin.
thymulin
A nonapeptide (Glu–Ala–Lys–Ser–Gln–Gly–Ser–Asn)
extracted from sera of humans and pigs and from calf
thymus. Thymulin shows a strong binding affinity for T cell
receptors on lymphocyte membranes. Its zinc-binding
property is associated with biological activity. Its enhancing
action is reserved exclusively for T lymphocytes. It facilitates
the functions of several T lymphocyte subpopulations
but mainly enhances T suppressor lymphocyte activity.
Formerly called FTS.
thymus
A triangular bilobed structure enclosed in a thin fibrous
capsule and located retrosternally. Each lobe is subdivided
by prominent trabeculae into interconnecting lobules and
comprises two histologically and functionally distinct
areas, cortex and medulla. The cortex consists of a mesh
of epithelial–reticular cells enclosing densely packed large
lymphocytes. It has no germinal centers. The epithelial cell
component is of endodermal origin; the lymphoid cells are
of mesenchymal origin. Prothymocytes that migrate from
the bone marrow to the subcapsular regions of the cortex
are influenced by this microenvironment that directs their
further development. The education process is exerted by
hormonal substances produced by thymic epithelial cells.
The cortical cells proliferate extensively. Some are shortlived
and die. The surviving cells acquire characteristics of
thymocytes. The cortical cells migrate to the medulla, then
to the peripheral lymphoid organs, sites of their main residence.
The medullary areas of the thymus are even richer
in epithelial cells, and the lymphocytes in the medulla are
loosely packed. The lymphocytes are small cells ready to
exit the thymus. Some remnants of epithelial islands, called
Hassall’s corpuscles, are histologically identifiable and are
6
ASP
11
ILE
19
LYS
O
C
HO
Structure of thymosin α-1.
7
THR
8
SER
10
GLU
20
LYS
28
ASP
9
SER
21
GLU
27
GLU
22
VAL
26
ALA
23
VAL
25
GLU
24
GLU