Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 124

the CD8 lineage [ 229 ]. Moreover, THPOK controls a positive feedback loop for

further THPOK expression by binding to and antagonizing the activity of THPOK
and CD4 silencer [ 227 ].

+

3.10.4.2 Unconventional ı Effector T Lymphocytes

γδ T cells represent a small subset of T lymphocytes that possess a plasmalemmal

T-cell receptor distinct from those of the majority of conventional T cells that are
composed of 2 glycoproteic

TCR chains. This group of uncommon T cells
lodges at its highest level in the gut mucosa, where it coexist with intra-epithelial
lymphocytes (IEL). A

α and β

γδ T-cell subpopulation resides in the epidermis, the so-called

dendritic epidermal T cells (DETC).

T lymphocytes expressing

γδ

T-cell receptors possess several features that make
them more similar to innate than adaptive immune effectors.

γδ

T cells use only
a tiny fraction of their potentially highly diverse TCR repertoire to recognize a
restricted set of antigens. In addition to recognition of a limited set of monomorphic
ligands,

γδ

T cells share with innate effectors the capacity to rapidly exert their
effector functions upon antigen encounter, even naive individuals [ 230 ]. They
indeed strongly and early on produce pro- or anti-inflammatory cytokines, such as
Ifn

γδ

, IL4, or IL17, that can control the early recruitment of innate effectors as well
as participate in the functional polarization of conventional

γ

αβ T cells and clearance

of eliciting pathogens.
γδ Effector T cells develop their function under the influence of innate pro-

gramming acquired during thymocyte maturation (that can be remodeled) and
environmental signals. They interact with immune and non-immune cells. They
bridge innate and adaptive immunity. They rapidly produce cytokines to regulate
pathogen clearance and inflammation [ 206 ]. They promote tissue repair and wound
healing. They recognize conserved non-peptide antigens. They have a tropism for
epithelia and mucosae such as those of the respiratory tract.
γδ

T cells yield distinct cytokine responses in different lymphoid organs. In mice,
experienced splenic

T cells that are predominantly CD122 high

γδ (interleukin-2 re-

ceptor β ) manufacture Ifn- γ [ 231 ]. On the other hand, naive lymph node γδ T cells

that are mainly CD122 low T cells acquire pro-

inflammatory functions without antigen encounter upon sensing of danger signals.
In addition, thymic selection determines the effector fate of

make interleukin-17. Therefore, γδ

γδ T cells rather than

constrains their antigen specificities.
γδ Effector T cells detect target molecules by T-cell (TCR), Toll-like (TLR),

and natural killer (NKR) receptors that act separately, synergistically, or addi-
tively [ 206 ]. Their

TCRs differ from one tissue to another for tissue-specific
antigen-recognition repertoires. 115

γδ

T cells carry out diverse functions, but cells
of subpopulations have more restricted effector properties, according to expressed
TCRs, cell location, and activation status.

γδ

115 Similarly to B- and

TCRs undergo somatic rearrangement of V
(variable), D (diversity), and J (joining) gene segments.

αβ T-cell receptors, γδ