Effector Functions of T cells

Question 1

T cells, which don’t recognize that antigen
T cells, which do recognise the specific antigen

Answer 1

Naive T cells tend to circulate through secondary lymphoid organs-lymph nodes where they might be presented their antigen by antigen presenting cells.
T cells, which don’t recognize that antigen being presented to them by APCs, will then just exit again the lymph node and go back into the circulation.
The T cells, which do recognise the specific antigen presented to them by antigen presenting cells and lose the ability to exit the lymph node so they remain there and start to proliferate and clone and expand and gain their immune effector functions.

Question 2

Naïve T cells activated by antigen presentation in secondary lymphoid organs proliferate and differentiate before exiting

Answer 2

LO Homing molecules enable T cells to enter LO through High endothelial venule (HEV)
CD62L and CCR7 interact with molecules expressed in HEV which enables them to traffic into the LN,
they first interact with these molecules on endothelium and then transmigrate through endothelium into LN via process similar to diapedesis

Question 3

Activation of naïve T cells requires a number of different signals

Answer 3

1st signal- interaction of TCR and CD4 with MHCII and peptide being presented, enabling Ag specific T cell response and activation.

Second signal- costimulatory signal- T cell receives through CD28- provided by CD80 or CD86 on surface of APC- trigger signaling pathways within the T cell that promote their survival and promote their metabolic activity

3rd signal- cytokine signal; APC secrete cytokines that bind to receptors on T cell and influence how T cell differentiates and what type of T cell it differentiates into

Question 4

Types of T cells
1.What Pathogens they target
2.What are the Triggers, What are the polarising cytokines that are causing the production of these T cells
3.What are the specific hallmark transcription factors that each one of them express
4.What are the typical cytokines released by each one of them which will ultimately help in clearing these pathogens

Answer 4

CD8 Cytotoxic cell
Target intracellular pathogens (virus, intracellular bacteria.
Compared to NK cells, CD8 T cells are antigen specific because they are required to recognise peptide antigen presented by MHC class one on the surface of either infected or cancerous cell.
Two major killing mechanisms:
1. Release of granules containing Perforin and Granzymes
-Granzyme B can activate Caspases
-Trigger the intrinsic apoptotic pathway through the mitochondria.
2. Interaction of Fas ligand (FasL) with Fas on the target cell

CD4+ Th1 cells
Extracellular Bacteria, and microbes in vesicles
IL12
T-bet
IFN-g
IFN-g stimulates infected macrophages to help control infection, by increasing:
MHC expression
Co-stimulatory molecule expression
Nitric Oxide (NO) production
Phagolysosome maturation
TNF-a production
Stimulating B-cells to produce antibodies

CD4+ Th2 cells
Parasites
IL2 and IL4
GATA3
IL4
IL-4 from Th2 cells promotes B cell class switching to IgE (allergic response)
IgE binds to the mast cell and causes the release of histamine.
The Th2 cells also release other cytokines that act on the other innate immune cells.

CD4+ Th17 cells
Fungi (and bacteria)
IL-1B
RORa
IL17
Increases neutrophil recruitment and controls epithelial barrier function

CD4+ T follicular helper (TFH) cells
Target all types
IL21
Bcl-6
Help the B cell
They convert them into plasma blasts and they also help them select the specific kind of antibody.

CD4+ T regulatory (TReg) cells
Suppress T-cell responses
Some thymic derived Treg binding self antigen
Peripheral derived Treg (pTReg)
pTReg differentiate in the presence of TGFb and retinoic acid
Express the transcription factor FoxP3
TReg suppress immune responses through
Cytokine consumption
Suppressive cytokine release
Suppression of antigen presenting cell function – inhibitory signalling, removal of co-stimulatory molecules, cytotoxicity

Question 5

Memory T Cells and Immune Response

Answer 5

Formation:
Memory T cells form after the resolution of an immune response, persisting long-term and providing rapid recall responses upon re-exposure to the same antigen.

Characteristics:
Effector Memory T Cells: Circulate in the periphery and respond quickly to infection.
Central Memory T Cells: Reside in lymphoid tissues and maintain long-term immunity.
Tissue-Resident Memory T Cells: Stay in specific tissues to provide immediate localized defense.