T cell differentiation, subsets, receptors Flashcards
if mature t cell expresses 10 million TCR molecules on its plasma membrane, how many antigen specificities would the cell express?
1
T and B cell lymphocytes begin to express antigen receptors …
as precursor cells in the primary lymphoid tissue following random recombination of genes
where are gamma-delta T cells found?
found as intraepithelial lymphocytes
What cytokines do Th1 cell produce?
Y-IFN
what cytokines do Th2 cells produce?
IL4, IL5, IL13
what cytokines do Th17 cells produce?
IL 17
IL 22
Where do Naive T cells encounter antigen?
In the paracortex of lymph nodes or the PALS of the spleen
when APCs and T cell travel to the lymph nodes this optimizes the interaction of antigen presentation
What happens upon Naive CD4 T cell activation?
after antigen presentation, there is clonal expansion and differentiation to either Th1, Th2 or Th17 cells
What type of infection do Th1 cells aid in?
intracellular
and aid in inflammtion
what type of infection doe Th2 cells aid in?
Parasitic - Helmiths
Allergic reactions
what type of infections do Th17 cells aid in?
Some bacteria and fungi
inflammatory disorders
extracellular pathogens
bring in additional neutrophils
what is the main leukocyte that Th1 cells recruit?
monocytes
what is the main leukocyte recruited by Th2 cells?
Eosinophils
what is the main leukocyte recruited by Th17 cells?
Neutrophils
monocytes
what kind of antibody isotypes are stimulated by Th1 cells?
complement
Fc receptor binding IgG subclasses
What types of antibody isotypes does Th2 stimulate?
IgE
IgG4
Naive CD4 T cells interact with antigen
presented on MHC II molecules by APCs in the secondary lymphoid tissue
List the steps of T cell activation
Antigen recognition Activation Clonal expansion Differentiation - during differentiation get effector and memory Effector functions
Effector CD4 T cells
activate macrophages and B cells
Effector CD8 T cell
Kill infected target cells
activate macrophages
where are T cells activated?
paracortex of lymph nodes
or PALS of spleen
what molecules are required for T cell activation?
APC - MHC2, CD80/86 (B7)
T cell - CD3, CD4, CD28, TCR
what are the three signals required for T cell activation? CD4 or CD8
signal 1 - interaction with MHC - adhesion molecules stabilize interaction.
signal 2 - co stimulation
signal 3 - cytokines from APC
In cell to cell interactions of activation of Cd4 cells, what molecules play a role in adhesion?
LFA-1 on CD4 T cells
ICAM-1 on the APC
What is absolutely required activation?
costimulation
CTLA4 interacts with
B7
when is IL 2 produced?
after antigen presentation but before proliferation
promotes T cell proliferation
positive feedback to the cell producing it
Naive CD4 T cell secretes IFN-y and IL-12 to induce
Th1 cells
Naive CD4 T cells release IL-4 to induce
Th2 cells
Naive CD4 T cells secrete TGF-b, IL-6 and IL-23 to induce
Th17 cells
IgE
attach to mast cells and Basophils and cross link to induce degranulation
also attracts Eosinophils
Th17 secretes IL-17 to influence
fibroblasts and endothelial cells to release cytokines to travel to Bone marrow upregulate neutrophils and chemokines to bring neutrophils to the area
During the activation of CD8 cells,what processes are happening?
The T cell is interacting with an APC presenting an ingested antigen (but remember that Dendritic cells can cross present)
this interaction induces it to proliferate. It is also being stimulated by CD4 helper cell cytokines such as IL2 and y-IFN to upregulate expression of granules and induce differentiation to mature effectors
Remember during clonal expansion that memory T cells are also being made
What is the danger of T cell activation by Superantigens?
superantigens can bind about 30% of Tcells. The induction of so many T cells can lead to a cytokine storm which can lead to septic shock
Upon activation by antigen presentation in MHC, what signal transduction activities occur?
CD3 on the cytosolic side is Phosphorylated (at ITAM?) leads to interactions with adaptor proteins which activates biochemical intermediates. Through PLC and GTP/GDP exchange, these increase Ca+2, DAG and Ras-GTP. These activate enzymes PKC, ERK, JNK which induce transcription factors - NFAT, NF-kB and AP-1 leading to transciption of cytokine genes
what is Buxton’s favorite transcription factor?
Nf-kB
how long does it take effector and memory T cells to leave the secondary lymph tissue?
days
Where does activation of effector T cells occur?
in the peripheral tissues
when a traveling T cell encounters an endothelial cell stop sign, what events then occur?
Tethering/rolling -> activation -> adhesion -> Transmigration
In general, cell mediated immunity events involve
release of cytokines
Macrophage activation - killing of those ingested microbes
inflammation
Killing of infected cells
Functions of Th1 cells
releases y-IFN to induce macrophage activation to enhance microbial killing and to induce B cells to IgG for opsonization to further enhance recognition and phagocytosis.
FcR
on professional phagocytes that recognize c3b and IgG on microbes
Activation of macrophages happens where?
in tissue
what events are occuring during the activation of macrophages by Th1 cells ?
Cd40L interacts with Cd40 on the macrophage
The T cell secretes y-IFN which influences the macrophage
What is the macrophages response to Th1 cell stimulation ?
enhanced killing of microbes by increasing expression of ROS and iNOS
increases expression of MHC molecules and costimulators (B7)
the macrophage secretes TNF, IL-1, chemokines, IL-12
what is the role of Th1 cells in inflammation?
through activating macrophages
cytokines are released from the macrophage that induce inflammation
What does IL-5 accomplish?
increases Eosinophils in the bone marrow
chemotactic for Eosinophils
what happens when IgE encounters a mast cell?
binds the mast cells, when enough are bound, they crosslink and cause degranulation and release of IL-5
What leukocyte cannot kill parasites?
Neutrophils
What cells do Th2 cells activate?
B cells
Eosinophils
Macrophages
What do Th2 cells indirectly activate?
Mast cells
The release of IL-4 from activated CD4 cells
induce the activated CD4 cells to proliferate and differentiate into Th2 cells
Th2 cells then secrete IL4, IL13, and IL5
What functions do Th2 cells carry out?
IL-4 release stimulates B cells to release neutralizing IgG antibodies and IgE, which activates Mast cell degranulation
IL-5 release causes Eosinophil activation allowing it to kill helminths
IL-4 and IL-13 together induce alternative macrophage activation leading to tissue repair and fibrosis
what molecules are important for effector CD4 T cell interactions?
CD40 ligand on the T cell
and CD40 on the Macs or B cell
What is the function of a Th17 cell?
secretes IL-17 which induces Leukocytes and tissue cells to secrete G-CSF, GM-CSF, CXCL1, CXCL8, TNF, IL-1 to induce a neutrophil response
What attracts neutrophils?
CXCL8
Th17 cells secrete IL-17 and IL-22, what happens?
Epithelial cells are induced to secrete anti-microbial peptides and increase barrier function
What do CD8 cells accomplish?
CTLs (CD8 T cell) find infected target cell and is activated
CTL granules exocytose and kill the target cells
What is the mechanism of the killing done by CTLs?
release granzymes which enter the target cells via receptor mediated endocytosis and enter via perforin dependent mechanisms
inside the target cell, these activate apoptotic pathways
What enters through the perforin holes created by CTLs?
Serine esterases
What increases the expression of MHC I on infected cells? what happens when this occurs?
y-IFN allows more expression of MHC I on infected cells, enhancing CTL detection and killing
what do regulatory T cells do?
secrete cytokines to Down regulate T cells and B cells
During activation, CD8 cells require
co-stimulation
and IL-2 from CD4 cells
what cells assists in the generation of acute inflammation by secreting cytokines to promote, recruit and activate neutrophils?
Th17
What cells activate macrophages to eradicate intracellular microbes?
Th1
What cells assist in the activation and differentiation of B cells ?
Th1 and Th2
y-IFN secretion from Th1 cells is essential for
production of IgG
IL-4 from Th2 cells is essential for
production of IgE
CD8 cells kill by using
granzymes, perforins, Fas-FasL interactions and lymphotoxins
How does mycobacteria evade the cell mediated immunity?
inhibiting the fusion of the phagosome and lysosome
How does Herpes evade the immune system?
inhibits antigen presentation by blocking TAP
How does EBV and Human CMV evade the immune system ?
inhibits proteosomal activity
CMV also removes MHC I molecules from the ER
what can EBV induce?
production of IL-10
cause inhibition of macrophages and dendritic cell activation
How does Pox virus manipulate the immune system?
inhibits effector cell activation
causes production of soluble cytokine receptors which binds of cytokines preventing them from activating effector cells