L9-T Cell Effector Responses Flashcards
(58 cards)
What is the role of T cells?
Plays a major role in cell mediated immunity in that it is important in eliminating and providing defense against intracellular microbes e.g. bacteria and viruses.
What is the main role for CD4+ T cells?
CD4+ T cells “help” activate macrophage to induce the production of ROS, NO, lysosomal enzymes to kill ingested microbes.
They also help to induce inflammation responses of other leukocytes to kill extracellular microbes e.g. fungi and helminths.
What is the main role for CD8+ T cells?
CD8+ T cells can recognise and kill the infected cells, thus eliminating the reservoir of infection.
How can you tell T cells apart?
- Categorised based on maturation state
2. Categorised based on function
Describe the maturation state of T cells.
Naive T cells (CD4+ or CD8+)
Meets antigen:
- Effector T cell or
- Memory T Cell
Memory cell:
- Effector memory T cell or
- Central Memory T cell
What are central memory T cells?
Central memory T cells (TCM cells) express CD45RO, C-C chemokine receptor type 7 (CCR7), and L-selectin (CD62L). … These memory T cells lack lymph node-homing receptors and are thus found in the peripheral circulation and tissues.
How are memory T cells different from naive T cells?
Memory T cells are a subset of infection- and cancer-fighting T cells (also known as a T lymphocyte) that have previously encountered and responded to their cognate antigen; thus, the term antigen-experienced T cell is often applied. In comparison to naive T cells, which are T cells that have not been exposed to antigens yet, memory T cells can reproduce to mount a faster and stronger immune response.
What happens to memory T cells once the infection has been cleared?
These cells would reverse from the active effector role to a state more similar to naive T cells and would be “turned on” again upon the next antigen exposure.
Why don’t memory T cells die after infection has been cleared, like effector T cells?
Memory T cells are instead produced by naive T cells that are activated, but never entered with full-strength into the effector stage.
The progeny of memory T cells are not fully activated because they are not as specific to the antigen as the expanding effector T cells.
Where can you find naïve T cells that have not yet encountered antigen?
Naïve T cells have not encountered an antigen and preferentially circulate through the secondary lymphoid organs (e.g. lymph nodes) via the lymphatics system.
Where does initial activation of naïve T cells occur?
Initial activation of naïve T cells usually occurs in secondary lymphoid organs (e.g. lymph nodes)
- When naïve T cells recognise their cognate antigens presented by antigen presenting cells
Why do memory T cells live longer than effector T cells?
Studies on T cell turnover indicate that most peripheral T cells can remain in a resting state for long periods (months in rodents and years in humans). Due to;
- Increased levels of anti-apoptotic proteins (e.g. Bcl-2)
- Undergo slow proliferation and able to self-renew
- Maintenance is dependent on cytokines only (e.g. IL-7)
What happens when naïve T cells are presented with antigen by a APC?
Naïve T cell that recognize the antigen undergo clonal expansion and differentiate into effector or memory T cells
What happens once effector T cells are activated?
- Enter blood circulation and preferentially migrate to peripheral tissue sites of infection
- Cells that recognize antigens in the tissues are retained and further activated to elicit their function.
NOTE: Migration of cells are mediated by chemokine and adhesion molecules.
After antigen recognition, 3 major processes must occur. What are they?
1) Produce cytokines and cytokine receptors (e.g. IL-2)
2) Proliferate and undergo clonal (TCR with same specificity) expansion
3) Differentiation into effector “short-lived” or memory “long-lived” cells
List some characteristics of memory T cells
1) Enhanced and more rapid responses to antigens than naïve T cell
2) Generate “new” effector T cells when re-encounter with the same antigen- e.g. Vaccination with inactivated or live attenuated virus or peptides
3) “Long-lived” T cells (compared to effector T cell)
4) Have different receptor expression patterns to naïve T cells.
What receptor patterns do naïve T cells have?
CD45RA+
CD25lo
CD127hi
What receptor patterns do effector T cells have?
CD45RO+
CD25hi
CD127lo
What receptor patterns do memory T cells have?
CD45RO+
CD25lo
CD127hi
What signals are required for T cell activation?
1) Antigens presentation (MHC ➡️ TCR)
- CD8 ➡️ MHC class I
- CD4 ➡️ MHC class II
2) Co-stimulatory molecules
- CD28 ➡️ B7 (CD80/86) = activation
- CTLA-4 ➡️ CD80/86 = inhibition
2) Cytokines
- Proliferation (IL-2)
- Differentiation (IFNγ + IL-12 ➡️ Th1)
What signal causes T cell inhibition?
CTLA-4 ligating with B7. It has higher affinity biding compared to CD28 to CD28 cannot bind.
Antigen presented by MHC class I on antigen-presenting cells is recognized by TCR on which type of T cells?
CD8+
Antigen presented by MHC class II on antigen-presenting cells is recognized by TCR on which type of T cells?
CD4+
Name an adhesion molecule on T cells
Leukocyte function-associated antigen-1; LFA-1
