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three-signal model of lymphocyte activation 695 Thy-1+ dendritic cells
It induced hepatic angiosarcoma, cholangiocarcinoma, and
hepatocellular carcinoma in some patients who received
it and it is known to produce other neoplasms. It has been
used in experimental animal studies involving the blockade
of the reticuloendothelial system. It is removed by the
reticuloendothelial (mononuclear phagocyte) system.
three-signal model of lymphocyte activation
A prototype accounting for the requirement by most lymphocytes
of three coordinated signals for total activation. The
signals are antigen recognition, costimulation, and cytokine
signaling. Usually, T cells require engagement by pMHC
for the first signal; costimulation by interaction of CD28
with B7-1/B7-2 for the second signal; and cytokine signaling,
often by IL2, as the third. B cells require interaction of
their receptors with antigen as the first signal; costimulation
by interaction of CD40 or CD40L expressed by an activated
antigen-specific Th cell as the second signal; and cytokine
signaling via cytokines released from Th cells as the third.
Threonyl transfer RNA synthetase antibodies.
threonyl transfer RNA synthetase antibodies
Antibodies against threonyl tRNA synthetase (threonyl
RS) protein that show high specificity for myositis. They
were demonstrated in 4% of polymyositis/dermatomyositis
patients. Antithreonyl RS antibodies have also been linked
to the antisynthetase syndrome characterized by fever,
Raynaud’s phenomenon, symmetrical arthritis, interstitial
lung disease, myositis, and mechanic’s hands.
threonyl transfer RNA synthetase autoantibodies
Autoantibodies (PL-7) to the 80-kDa threonyl tRNA synthetase
protein that are highly specific for myositis. PL-7
autoantibodies have been found with autoantibodies against
aminoacyl tRNA synthetases including histidyl, alanyl,
isoleucyl, and glycyl tRNA synthetases, and are associated
with the antisynthetase syndrome characterized by acute
onset steroid-responsive myositis with interstitial lung disease,
fever, symmetrical arthritis, Raynaud’s phenomenon,
and mechanic’s hands.
thrombocyte
Blood platelet.
thrombocytopenia
Diminished blood platelet numbers with values below
100,000/cm 3 of blood compared to a normal value of
150,000 to 300,000/cm 3 . This decrease in blood platelets
can lead to bleeding.
thrombocytopenic purpura, idiopathic
An autoimmune disease in which antiplatelet autoantibodies
destroy platelets. Splenic macrophages remove circulating
platelets coated with immunoglobulin G (IgG) autoantibodies
at an accelerated rate. Thrombocytopenia occurs
although the bone marrow increases platelet production,
which can lead to purpura and bleeding. The platelet count
may fall below 20,000 to 30,000/μL. Antiplatelet antibodies
are detectable in sera and on platelets. Platelet survival
is decreased. Splenectomy is recommended in adults.
Corticosteroids facilitate a temporary elevation in platelet
count. This disease is characterized by decreased blood
platelets, hemorrhage, and extensive thrombotic lesions.
thrombocytosis
Elevated blood platelet numbers with values exceeding
600,000/cm 3 of blood compared to a normal value of
150,000 to 300,000.
thromboxanes
A group of biologically active compounds that play a physiological
role in homeostasis and a pathophysiological role in
thromboembolic disease and anaphylactic reactions. They are
cyclopentane derivatives of polyunsaturated fatty acids derived
by isomerization from prostaglandin endoperoxide PGH 2,
the immediate precursor. The isomerizing enzyme is called
thromboxane synthetase. The active compound, thromboxane
A 2, is unstable, degraded to thromboxane B 2, which is stable
but inactive on blood vessels, but has polymorphonuclear cell
chemotactic activity. The short notations are TXA 2 and TXB 2.
Both compounds represent the major pathway of conversion
of prostaglandin endoperoxide precursors. The level of TXA 2,
derived from prostaglandin G 2 generated from arachidonic
acid by cyclooxygenase, increases following injury to vessels.
TXA 2 stimulates a primary hemostatic response and
is a potent inducer of platelet aggregation, smooth-muscle
contraction, and vasoconstriction. TXA 2 was previously called
rabbit aorta contacting substance (RACS). It is isolated from
lung perfusates during anaphylaxis. It appears to be a peptide
containing fewer than ten amino acid residues. Thromboxane
formation in platelets is associated with the dense tubular
system. Polymorphonuclear neutrophils (PMNs) and spleen,
brain, and inflammatory granulomas have been demonstrated
to produce thromboxanes.
thy ()
Epitope found on murine thymocytes and most murine T
lymphocytes.
antigen
Refer to Thy-1 antigen.
Thy-1
A murine and rat thymocyte surface glycoprotein found also
in neuron membranes of several species. Thy-1 was originally
called θ alloantigen. Thy.1 and Thy.2 are the allelic forms. A
substitution of one amino acid, arginine or glutamine, at position
89 represents the difference between Thy1.1 and Thy1.2.
Mature T cells and thymocytes in mice express Thy-1. The
genes encoding Thy-1 are present on chromosome 9 in mice.
Although few human lymphocytes express Thy-1, it is present
on the surfaces of neurons and fibroblasts.
Thy-1 antigen
A murine isoantigen present on the surfaces of thymic
lymphocytes and on thymus-derived lymphocytes found in
peripheral lymphoid tissues. Central nervous system tissues
may also express Thy-1 antigen.
Thy-1+ dendritic cells
Cells derived from the T lymphocyte lineage and found
within the epithelium of murine epidermis.
T