T Lymphocyte Development Flashcards

Flashcards for reviewing T lymphocyte development, covering TCR structure, T cell development stages, selection processes, and T cell subsets.

TCR (T cell Receptor)

Receptor on T cells, similar to BCR in B cells, specific for antigens.

Valence and conformation Differences between TCR and BCR

TCR is a 2-chain structure with a single binding site; BCR is a 4-chain structure, allowing it to bind bivalently to antigens.

Antigen Recognition Differences between TCR and BCR

BCR recognizes carbohydrates, proteins, etc., in fluids; TCR interacts with small peptides in association with MHC on host cells.

Secretion differences between TCR and BCR

Unlike BCR, TCR does not exist in a secreted form.

Change in TCR during response to antigens Differences between TCR and BCR

BCR undergoes somatic hypermutation and class switching; TCR does not change during the immune response.

TCR complex

Complex formed by TCR chains expressed on T cells in noncovalent association with CD3 and zeta (ζ) chains.

Coreceptor molecules: CD4 and CD8

Transmembrane molecules on mature T cells (CD4+ or CD8+) that enhance the ability of antigen to activate T cells.

Binding specificity of CD4 and CD8

CD4 binds to MHC class II molecules, while CD8 binds to MHC class I molecules.

VDJ recombinase and RAG 1 and 2

Enzymes involved in multiple gene segments, somatic DNA random recombination, Junctional flexibility, Insertional variability, and interchain combination diversity contributing to TCR diversity.

Thymus

Site of T cell differentiation, which diminishes after puberty.

T cell differentiation

Occurs throughout life but diminishes significantly after puberty.

Pro-T cells

TCR genes of b start to rearrange here. Express no CD4 or CD8 molecules (double negative cell)

Pre- T cells

Express the TCR b chain in association with an invariant molecule Pre-Tα. The combination with CD3 makes the Pre- TCR analogous to the pre-BCR.

Immature double positive T Cells

Expression of CD4 and CD8 forming these cells. Expression of TCR αb with CD3. Undergo thymic selection

Thymic Selection

Two major stages that include positive and negative selection, determining T cell survival and self-tolerance.

Positive Selection

DP cells interact with self-MHC I & II and self- peptide molecules. This interaction results in the survival of the DP cell. The affinity determines the outcome

Negative Selection

Occurs when dp cell interact with dendritic cells in the medulla. A DP cell that reacts with too high affinity to the combination of MHC and self peptide is deleted by apoptosis.

Self-tolerance to molecules normally found outside the thymus

Including thyroglobulin (thyroid), insulin (the pancreas) and myelin basic protein (CNS) are expressed by thymic epithelial cells in the medulla

AIRE gene

Codes for a protein that controls the expression of self- molecules in the thymus which helps develop Self-tolerance to molecules normally found outside the thymus

Single Positive (SP) Cells

DP T cells that survive negative selection, down-regulate expression of either CD4 or CD8 resulting in these cells in the medulla

self-MHC restricted

T cells respond to an Ag only when associated with the MHC molecules

self-tolerant

Mature CD4 or CD8 T cells do not respond to self components.

CD28 of T

Interact with B7 on APC: necessary for IL-2 synthesis

LFA-1

Lym function Ag interact with ICAM expressed on endothelial cells and APC. Expressed on all mature T cells

Homing molecules

Entry of naïve lym to L. nodes is mediated by the expression of the same set of adhesion molecules and chemokine receptors expressed by naïve B cells.

ϒδ Cells

Minor population expresses distinct 2-chain ϒδ TCR in association with CD3. Lack the CD4 and CD8 coreceptor and not MHC restricted

NK cells

Develop in the thymus from the same bone marrow precursor that gives rise to the T cell lineage. Involved in the early phase of i.r. and considered part of innate immunity that kill viral-infected cells and tumor cells.

NKT Cells

Small subset of T cells (1% of blood mononuclear cells), express both a TCR and NK1.1 (mouse) or CD16 (human) characteristic of NK cells. Have features of both the innate and adaptive immune defenses.

Treg cells

A subset of CD4+ T cells, approximately 10% of CD4 cells that express CD25 and the transcription factor foxp3.