- T cells develop from these cells and migrate in waves to the thymus where they mature

Bone Marrow Stem Cells

- these cytokines influence proliferation and differentiation of T cells

IL-3, IL-7

- the specific thymic hormone involved in T cell development

thymosin

- rate of thymus involution

3%/yr

- this occurs when the thymus fails to develop and a T-cell immunodeficiency is present

- B lymphocyte production is normal

DiGeorge's syndrome

- this marker is observed on undifferentiated pluripotential hematopoietic stem cells

- allows for identification of hematopoietic stem cells

- NOT committed to T-cell lineage yet

CD34

- interaction with these cells causes progenitor cells to divide and subsequently lose their CD34 marker in the outer cortical region

Thymic Stromal Cells

- the journey from cortex to medulla in the thymus is facilitated initially by these cells

nurse cells (specialized epithelial cells)

 - all T lymphocytes and Natural Killer cells express this marker

CD2

- appears shortly after CD2 receptor

- adhesion molecule involved in cell-cell interaction, migration and peripheral lymph node homing

- expressed 10-fold on activated T and B cells

- many cancer cell types express high levels of this

CD44

- binds to CD34

- excreted by thymic stromal cells and critical for T & B-cell development

- stimulates the differentiation of pluripotential hematopoietic stem cells into lymphoid progenitors

IL-7

- cytokine that directs myeloid progenitor cell differentiation

IL-3

- thymocyte cell-surface receptor that binds ligands on thymic epithelial cells

- major regulator required for T-cell development

Notch1

- the major regulator required for B-cell development that keeps the cell on the B-cell differentiation pathway

Pax-5

- early transient marker for T-cell development

- is utilized in creating the recombinatorial diversity in the variable regions of the TcR chains

- disappears following rearrangement

TdT

- T-cell receptors are found on both T helper and T cytotoxic cells and consist of these components

a & B chain with variable and constant region

- after 1 week of dividing in this region of the thymus T cells begin to bear TcR2 (aB) and TcR1 (yd)

Subcapsular region

- earliest T-cell populations do not express CD4 or CD8 and are described as this

- small number of these actually express genes for (yd T-cel receptors)

"Double Negative"

(CD4- & CD8-)

- order by which the TcR, CD4 and CD8 appear on cell surface

TcR ==> CD4/CD8

- these type of T-cell receptors do not require MHC-epitopes to function

- can usually be found in the epithelial boundaries (gut)

- secrete CYTOKINES

yd T-cell receptors

- the V and J gene segments (analogous to antibody light chains) code for these two components of TcR

- found on chromosome # 14

a & y

(alpha and gamma)

- the V, D and J gene segments (analogous to antibody heavy chains) code for these two components of TcR

- found on chromosome # 7

B & d

(beta and delta)

- similar to Iga and IgB in that this protein complex is invariant and does not bind antigens

CDR

- the CD3 complex is only found on T lymphocytes and originates as a "chaperone" for TcR from this region of the cell to the surface

Cytoplasm

- this TcR component's rearrangement is an early marker for early thymocytes

TcR-beta chain

- docking sites for intracellular protein kinases that are found in the CD3 chains

immunoreceptor tyrosine-based motif (ITAM)

- these double negative T cells express NK1.1 receptor that is also found on NK cells

- reside in large numbers in the liver, bone marrow, and thymus

NK1.1+ T Lymphocytes

NK1.1+ T Lymphocytes produce high levels of these cytokines in the liver, bone marrow, and thymus

IL-4, IFNy and TNFa

- NKT cells recognize this type of antigen that is presented by this type of molecule

- this process allows for NKT cells to perform innate and acquired immunity function

- NKT cells perform the function of both T helper and T cytotoxic lymphocytes

glycolipid antigen presented by CD1d

- double positive lymphocytes express all of these surface markers/receptors

CD4, CD8, TcR

- as lymphocytes progress towards the medulla they progress from this state to differentiated as either CD4+ or CD8+

"Double Positive"

-the ratio of CD4 to CD8 lymphocytes is this

- this contributes to being a marker in recognizing HIV/AIDS or other immunodeficiencies

2:1

- HIV binds to this of the 4 CD4 Ig-like domains

D1 region

- CD4 is essential for this MHC Class docking and epitope recognition

Class II

- CD8 consists of these two chain connected by a disulfide bond (heterodimer)

alpha and beta

- CD4 and CD8 function as this component of the receptor complex

- activate signal transduction when proper fit is established

docking by way of adhesion molecules

- over activation of T-cells is instigated by these proteins that bind outside the MHC cleft and then overproduce cytokines

- Example: staphyloccal toxin

Superantigens

- these T lymphocytes help to "suppress" T-cells and their immune response

Tregs (CD4+)

- the receptor for IL-2 that in conjunction with CD4 helps to suppress the immune response of T cells

CD25 (CD4+CD25+)

- Tregs regulate other CD4 T cells when they bind this molecule

the same antigen (APC) as the CD4 T cell

- the process of "self" and "nonself" selection is described by this process

Tolerization

- TcRs must recognize (or not recognize) these two things to be effective at reacting to specific antigen and not reacting to "self"

epitopes in the MHC cleft

MHC polymorphic sites ("self")

- this takes place in the cortex and tests the TcR for their binding capabilities

- with a strong binding the T lymphocyte lives

- a weak binding, it does

Positive Selection

- process where if TcR binds too strongly to the self-MHC complex it dies

- presented primarily by dendritic cells and macrophages

Negative Selection