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T lymphocyte antigen receptor (TCR) 707 TNF receptors
afferent limb of the immune response to exogenous antigen
delivered to them by antigen-presenting cells. This stimulates
the synthesis of interleukin-2 (IL2), which activates CD8 + T
cells, natural killer (NK) cells, and B cells, thereby orchestrating
an immune response to the antigen. Thus, they are
termed helper T lymphocytes. They also mediate delayedtype
hypersensitivity reactions. CD8 + T lymphocytes include
cytotoxic and suppressor cell populations. They react to
endogenous antigen and often express their effector function
via a cytotoxic mechanism (e.g., against a virus-infected cell).
Other molecules on mature T cells in humans include the E
rosette receptor CD2 molecule, T cell receptor, pan-T cell
marker termed CD3, and transferrin receptors.
T lymphocyte antigen receptor (TCR)
The two types of T cell antigen receptors are TCR1 (appears
first in ontogeny) and TCR2. TCR2 is a heterodimer of α and
β polypeptides. TCR1 consists of γ and δ polypeptides. Each of
the two polypeptides comprising each receptor has a constant
and a variable region (similar to immunoglobulin). Reminiscent
of the diversity of antibody molecules, T cell antigen receptors
can likewise identify a tremendous number of antigenic
specificities (estimated at 10 15 epitopes). The TCR is composed
of a minimum of seven receptor subunits whose production
is encoded by six separate genes. Following transcription,
these subunits are assembled precisely. Assimilation of the
complete receptor complex is requisite for surface expression
of TCR subunits. Numerous biochemical events are associated
with activation of a cell through the TCR. These events
ultimately lead to receptor subunit phosphorylation. T cells may
be activated by the interaction of antigen in the context of the
major histocompatibility complex (MHC) with T cell receptors,
involving transmission of a signal to the interior through the
CD3 protein to activate cells.
T lymphocyte–B lymphocyte cooperation
The association of T and B cells through a number of
receptor–ligand interactions at the surfaces of both cell
types, culminating in the synthesis by B cells of antibody
specific for thymus-dependent antigens.
T lymphocyte clone
Daughter cells of one T lymphocyte derived from the blood
or spleen that are added to culture medium and activated by
antigen. T cells stimulated by the antigen form blasts that
can be separated from the remaining T cells by density gradient
centrifugation. T cells that have responded to antigen
are diluted, and aliquots are dispensed into tissue culture
plates to which antigen and interleukin-2 (IL2) are added.
Each well contains a single lymphocyte. This method provides
individual T cell clones.
T lymphocyte-conditioned medium
A cell culture medium containing multiple lymphokines
released from T cells stimulated by antigens or lectins.
T lymphocyte hybridoma
Produced by fusing a murine splenic T cell and an AKR
strain BW5147 thymoma cell using polyethylene glycol
(PEG). The hybrid cell clone is immortal and releases
interleukin-2 (IL2) when activated by antigen provided by
an antigen-presenting cell.
T lymphocyte receptor
Refer to T lymphocyte antigen receptor.
T lymphocyte subpopulation
A subset of T cells that have a specific function and express
a specific cluster of differentiation (CD) markers or other
antigens on their surfaces. Examples include the CD4 +
helper T lymphocyte subset and the CD8 + suppressor/cytotoxic
T lymphocyte subset.
T lymphocytes
Synonym for T cells. T lymphocyte precursors are detectable
in a human fetus at 7 weeks of gestation. Between
weeks 7 and 14 of gestation, thymic changes begin to
imprint thymic lymphocytes as T cells. The maturation
(mediated by hormones such as thymosin, thymulin, and
thymopoietin II) may be followed by identification of
surface (cluster of differentiation [CD]) markers detectable
by immunophenotyping. CD3, a widespread T cell marker,
serves as a signal transducer from the antigen receptor to
the cell interior. Thus, CD3 is intermittently associated
with the T cell receptor for antigen. T lymphocytes in the
medulla initially express both CD4 and CD8 class markers
but these cells later differentiate into CD4 + helper cells or
CD8 + suppressor cells. The CD4 + cells characterized by
55-kDa surface markers communicate with macrophages
and B cells bearing major histocompatibility complex
(MHC) class II molecules during antigen presentation.
The CD8 + suppressor/cytotoxic cells interact with antigenpresenting
cells bearing MHC class I molecules.
T lymphocyte–T lymphocyte cooperation
Signals from one T lymphocyte subpopulation to another,
e.g., isotype class switching in the regulation of immunologic
responsiveness.
Tm
Membrane immunoglobulin heavy chain tail (C terminal)
polypeptide.
T6 marker
A chromosome of CBA/H-T6 inbred mice discovered in an
irradiated male. It has been used as a cell marker to trace
cells transferred to other mice. Its length is abbreviated and
it has a secondary constriction adjacent to the centromere.
TNF
Abbreviation for tumor necrosis factor.
TNF-
Abbreviation for tumor necrosis factor α.
TNF-
Abbreviation for tumor necrosis factor β.
TNF receptor-associated factors (TRAFs)
Adaptor molecules that interact with cytoplasmic domains
in TNF receptor molecules. This family includes tumor
necrosis factor (TNF)-RII, lymphotoxin (LT) β receptor,
and CD40. Cytoplasmic motifs in these receptors bind
separate TRAFs that interact with other signaling molecules,
resulting in transcription factor AP-1 and NF-κB
transcription factors.
TNF receptor-associated periodic syndrome (TRAPS)
A primary autoinflammatory immunodeficiency defined
by repeated episodes of severe localized inflammation and
extended bouts of fever. Attributable to TNGR1 mutations
that lead to uncontrolled activation of the TNRF1 pathway.
TNF receptors
Tumor necrosis factor (TNF) receptors interact with three
structurally related ligands: TNF-α, lymphotoxin α (LTα)
or TNF-β, and LTβ. Two of the three have the designations
CD120a (type I, p55 or p60 receptor) and CD120b (type II,
p75 or p80 receptor). The third is designated LTβ receptor
(LTβ-R), type III TNF receptor, or TNFR-RP. TNF receptors
may be cell-bound or soluble. CD120a and CD120b
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