Biology of T lymphocytes

Question 1

the thymus is where

Answer 1

T cells are educated

Question 2

T cell eduation

Answer 2

• T cell acquires TCR (antigen specificity)
• learns tolerance of self
• learns HLA-restriction

Question 3

DiGeorge’s syndrome

Answer 3

small thymus, no thymus so low T cells
this is immunodeficiency syndrome

Question 4

thymic involution occurs

Answer 4

post-puberty

Question 5

Positive selection of T lymphocyte ontogeny

Answer 5

CD4 and CD8 immature thymocytes must bind HLA class I and HLA class II on thymic epithelial cells with “just the right” affinity. if not they undergo apoptosis and die
- learns self HLA restriction

Question 6

Negative selection of T lymphocyte ontogeny

Answer 6

Cells that remain from positive selection and respond to self HLA presenting self peptide on interdigitating dendritic cells undergo apoptosis and die or become anergic (tolerance)

Question 7

central T lymphocyte tolerance

Answer 7

• tolerance learned during ontogeny is called central tolerance
• involves immature double-positive T cells
• strong recognition to antigens results in apoptosis
• remember antigens present in the thymus are almost always self antigens

Question 8

Circulation of mature naive T cells

Answer 8

• specific receptor-ligand interactions between lymphocytes and endothelial cells occur that mediate recirculation and homing of lymphocytes
• if, while filtering through a lymph node, a T cell encounters an APC expressing HLA + foreign peptide - it may respond or not
• responses = activation
• tolerance = no activation

Question 9

Activation of T lymphocytes
B cells tend to deal with

Answer 9

extracellular antigens

Question 10

Activation of T lymphocytes
T cells respond to

Answer 10

intracellular or cell-associated antigens

Question 11

Activation of T lymphocytes

Answer 11

upon encountering antigen, T cells become activated
- CD4 T helper cells produce cytokines
- CD8 cytotoxic cells kill cells expressing a foreign antigen

Question 12

T cell antigen receptor complex (TCR)

Answer 12

• member of the Ig supergene family
• composed of alpha and beta chains
• has conserved and variable domains
• recognizes Ag + HLA on APC

Question 13

TCR complex is comprised of

Answer 13

TCR (movie star)
CD3 (entourage)
zeta chains (CD247)

Question 14

T cell antigen receptor complex (TCR)
CD3:

Answer 14

• composed of gamma, epsilon, delta chains
• complex is found on all mature T lymphocytes
• chaperone for TCR
• critical signaling molecule

Question 15

TCR complex
Zeta chains

Answer 15

signaling molecules

Question 16

Co-receptors for T cell activation
CD4 facilitates binding of

Answer 16

HLA class II molecules to the TCR

Question 17

Co-receptors for T cell activation
CD8 facilitates binding of

Answer 17

HLA class I molecules to the TCR

Question 18

Positive co-stimulatory interactions

Answer 18

B7(CD80):CD28
CD40:CD40L (CD154)

Question 19

Negative co-stimulatory interactions

Answer 19

PD-L1:PD-1
B7(CD80): CTLA-4

Question 20

Peripheral T cell tolerance:
Anergy

Answer 20

functional inactivation of T cells
occurs when primary signal (MHC/peptide-TCR binding) happens without secondary signal
secondary signal is needed to stabilize IL-2 mRNA

Question 21

Peripheral T cell tolerance:
activation-induced cell death

Answer 21

activated T lymphocytes will die by apoptosis if repeatedly stimulated with antigen
- induces expression of Fas and Fas ligand resulting in apoptosis
- expression of pro-apoptotic proteins resulting in apoptosis

Question 22

Peripheral T cell tolerance:
Regulatory T cells

Answer 22

• CD4+, CD25+, and FoxP3+
• suppress or inhibit the activation of other T cells
• most likely due to the production of inhibitory cytokines