T-cell receptor (TCR) The cell-surface receptor for antigen on T lymphocytes. It consists of a disulfide-linked heterodimer of the highly variable α and β chains in a complex with the invariant CD3 and ζ proteins, which have a signaling function. T cells carrying this type of receptor are often called α:βT cells. An alternative receptor made up of variable γ and δ chains is expressed with CD3 and ζ on a subset of T cells.
T-cell receptor α (TCRα) and β (TCRβ) The two chains of the α:β T-cell receptor.
T-cell receptor excision circles (TRECs) Circular DNA fragments excised from the chromosome during V(D)J recombination in developing thymoctytes that are transiently retained in T cells that have recently left the thymus.
T-cell zones See T-cell areas.
T-DM1 An antibody-drug conjugate combining trastuzumab (Herceptin) with mertansine used to treat recurrent metastatic breast cancer previously treated with a different trastuzumab drug conjugate.
TdT See terminal deoxynucleotidyl transferase.
TEPs See thioester-containing proteins.
terminal deoxynucleotidyl transferase (TdT) Enzyme that inserts nontemplated N-nucleotides into the junctions between gene segments in T-cell receptor and immunoglobulin V-region genes during their assembly.
tertiary immune responses Adaptive immune response provoked by a third injection of the same antigen. It is more rapid in onset and stronger than the primary response.
T follicular helper (TFH) cell An effector T cell found in lymphoid follicles that provides help to B cells for antibody production and class switching.
TH1 A subset of effector CD4 T cells characterized by the cytokines they produce. They are mainly involved in activating macrophages but can also help stimulate B cells to produce antibody.
TH2 A subset of effector CD4 T cells that are characterized by the cytokines they produce. They are involved in stimulating B cells to produce antibody, and are often called helper CD4 T cells.
TH17 A subset of CD4 T cells that are characterized by production of the cytokine IL-17. They help recruit neutrophils to sites of infection.
thioester-containing proteins Homologs of complement component C3 that are found in insects and are thought to have some function in insect innate immunity.
thioredoxin (TRX) A set of sensor proteins normally bound to thioredoxininteracting protein (TXNIP). Oxidative stress causes thioredoxin to release TXNIP, which can mediate downstream actions.
thioredoxin-interacting protein (TXNIP) See thioredoxin.
thymectomy Surgical removal of the thymus.
thymic anlage The tissue from which the thymic stroma develops during embryogenesis.
thymic cortex The outer region of each thymic lobule in which thymic progenitor cells (thymocytes) proliferate, rearrange their T-cell receptor genes, and undergo thymic selection, especially positive selection on thymic cortical epithelial cells.
thymic stroma The epithelial cells and connective tissue of the thymus that form the essential microenvironment for T-cell development.
thymic stromal lymphopoietin (TSLP) Thymic stroma-derived lymphopoietin. A cytokine thought to be involved in promoting B-cell development in the embryonic liver. It is also produced by mucosal epithelial cells in response to helminthic infections, and promotes type 2 immune responses through its actions on macrophages, ILC2s, and TH2 cells.
thymocytes   Developing T cells when they are in the thymus. The majority are not functionally mature and are unable to mount protective T-cell responses.