T cell activation and differentiation Flashcards
1
Q
Activation of Naïve T cells occurs where?
A
• occurs exclusively in secondary lymphoid tissues
2
Q
For Activation of Naïve T cells, what signals are required?
A
TCR recognition of cognate peptide:MHC complex
co-stimulation signal (B7 binding to CD28)
3
Q
For Activation of Naïve T cells, naïve T cells can only be activated by what? why is this important?
A
professional antigen-presenting cells (APCs)
•• APC are the only cells that express B7 molecules
4
Q
Describe the steps of trafficking of naive T cells
A
- T cells enter a lymph node across high endothelial venules in cortex
- T cells monitor anitgen presented by macrophages and dendritic cells
- T cells that do not encounter specific antigen leave the node in the efferent lymph
- T cells that encounter specific antigen proliferate and differentiate to effector cells
5
Q
What directs lymphocyte trafficking?
A
adhesion molecules
6
Q
• there are 4 classes of cell-surface adhesion molecules. Name them
A
- selectins
- mucin-like vascular addressins
- integrins
- Ig superfamily members
7
Q
Describe the adhesion molecule: selectin. give examples
A
lectins that bind to carbohydrates
• L-selectin, P-selectin
8
Q
Describe the adhesion molecule: Mucin-like vascular addressins. give examples
A
have carbohydrate moities (targets for selectin binding)
• CD34, GlyCAM-1, MAdCAM-1
9
Q
Describe the adhesion molecule: Integrins. give examples
A
bind to various cell adhesion molecules
• lymphocyte function-associated antigen (LFA-1)
10
Q
Describe the adhesion molecule: Immunoglobulin superfamily members. give examples
A
targets for integrin binding
• intracellular adhesion molecules (ICAMs), CD2, LFA-3
11
Q
Describe the process adhesion molecules direct lymphocyte trafficking
A
- Circulating T cell enters the high endothelial venule in lymph node
- Binding of L-selectin to GlyCAM-1 and CD34 allows rolling interaction
- LFA-1 is activated by chemokines bound to ECM
- activated LFA-1 binds tightly to ICAM-1
- diapedesis => lymphocyte leaves blood and enters lymph node
12
Q
What are the professional APCs?
A
dendritic cells, macrophages, B cell
13
Q
Name what it attacks, the location in the lymph node, how antigen is uptaken, MHC expression, co-stimulator delivery, how antigen is presented, and location within body of dendritic cells
A
- cell attacked => viral antigen
- location in lymph node => T cell areas
- antigen uptake => major macropinocytosis and phagocytosis by tissue dendritic cells, and viral infection
- MHC expression => low on tissue DCs, High on DCs in lymphoid tissues
- co-stimulator delivery => constitutive by mature, nonphagocytic lymphoid DCs
- antigen presented => peptides, viral antigens, allergens
- location => ubiquitous throughout body
14
Q
Name what it attacks, the location in the lymph node, how antigen is uptaken, MHC expression, co-stimulator delivery, how antigen is presented, and location within body of macrophages
A
- cell attacked => bacterium
- location in lymph node => throughout lymph node
- antigen uptake => phagocytosis
- MHC expression => inducible by bacteria and cytokines from neg to very strong
- co-stimulator delivery => inducible from neg to very strong
- antigen presented => Particulate antigens, Intracellular and extracellular pathogens
- location => lymphoid tissue, connective tissue, body cavities
15
Q
Name what it attacks, the location in the lymph node, how antigen is uptaken, MHC expression, co-stimulator delivery, how antigen is presented, and location within body of B cells
A
- cell attacked => microbial toxin
- location in lymph node => follicle
- antigen uptake => antigen-specific receptor (Ig)
- MHC expression => constitutive and increases on activation
- co-stimulator delivery => inducible from negative to very strong
- antigen presented => soluble antigens, toxins, viruses
- location => lymphoid tissue, peripheral blood
16
Q
Describe how DCs stimulate naive T cells
A
- antigen uptake by Langerhans cells in skin
- Langerhans cells leave skin and enter lymphatic system
- mature DCs enter lymph node from infected tissued and transfer some antigens to resident DCs
- B7-positive DCs stimulate naive T cells
17
Q
What are the 5 mechanism of which antigen processing/presentation for DCs can be utilized?
A
- receptor mediated endocytosis
- macropinocytosis
- viral infection
- cross-presentation after phagocytic or macropinocytic uptake
- transfer from incoming DCs to resident DCs
18
Q
Name the type of pathogen presented, MHC molecules loaded, type of naive T cell activated wrt DCs using the route of receptor-mediated endocytosis
A
type of pathogen presented: extracellular bacteria
MHC molecules: MHC II
Type of naive T cell activated: CD4 T cells
19
Q
Name the type of pathogen presented, MHC molecules loaded, type of naive T cell activated wrt DCs using the route of macro-pinocytosis
A
type of pathogen presented: extracellular bacteria, soluble antigens, virus particles
MHC molecules: MHC II
Type of naive T cell activated: CD4 T cells
20
Q
Name the type of pathogen presented, MHC molecules loaded, type of naive T cell activated wrt DCs using the route of viral infection
A
type of pathogen presented: viruses
MHC molecules: MHC I
Type of naive T cell activated: CD8 T cells
21
Q
Name the type of pathogen presented, MHC molecules loaded, type of naive T cell activated wrt DCs using the route of cross-presentation after phagocytic or macropinocytic uptake
A
type of pathogen presented: viruses
MHC molecules: MHC I
Type of naive T cell activated: CD8 T cells
22
Q
Name the type of pathogen presented, MHC molecules loaded, type of naive T cell activated wrt DCs using the route of transfer from incoming DCs to resident DCs
A
type of pathogen presented: viruses
MHC molecules: MHC I
Type of naive T cell activated: CD8 T cells
23
Q
Describe the process of how Dendritic Cells (and Macrophages) Take Antigen to 2˚ Lymphoid Tissues
A
- DCs take up bacterial antigens in skin and move to enter a draining lymphatic vessel
- DCs bearing antigen enter draining lymph node where they settle in T cell areas
24
Q
Describe antigen presentation by B cells
A
- antigen specific B cell binds antigen
- specific antigen efficiently internalized by receptor-mediated endocytosis
- high density of specific antigen fragments presented
25
T/F Adhesion Molecules Initiate Cell-Cell Interactions
true
26
Of the Ig superfamily, what is an intercellular adhesion molecule?
ICAMs
27
Describe the 3 steps of how adhesion molecules initiate contact for DCs
1. T cell initially binds DCs through low-affinity LFA-1 : ICAM-1 interactions
2. subsequent binding of TCRs sends signal to LFA-1
3. conformational change in LFA-1 increases affinity and prolongs cell-cell contact
28
Describe the co-stimulatory molecule binding to naive T cell
co-stimulatory molecule B7 on the DC binds CD28 on naive T cell
29
What are the 1st and 2nd signals of activation for naive T cells?
1. Recognition of cognate peptide:MHC complex on surface of APC thru the TCR
2. Interaction between CD28 on T cell with B7 (co- stimulator) on APC
30
What is an autocrine T cell growth factor? What is the result? When does this occur?
Interleukin-2
(IL-2)
Proliferation/Differentiation
occurs after stimulation of naive T cell
31
Describe how IL-2 is a growth signal for T cells (4 steps)
1. naive T cells express low affinity IL-2 receptor
2. Activated T cells express the high affinity IL-2 receptor and secrete IL-2
3. binding of IL-2 to high-affinity receptor sends a signal to T cell
4. signal sent from IL-2 receptor induces T cell proliferation
32
What is the difference of the structure of the IL-2 receptor between a naive T cell and activated T cell?
* it gets higher affinity due to the addition of the IL-2 receptor of the alpha chain being added to the activated T cell
33
T/F some self-reactive T cells escape the negative selection process (thymus)
true
34
What is required for T cell activation? describe its expression. When is it upregulated?
B7 co-stimulation signaling is required for T cell activation
## Footnote
•• B7 expression is inducible
upregulated when potential pathogen is recognized via pattern-recognition receptors
(signaling thru Toll-like receptors)
35
Activation signals for naive T cells can occur via co-stimulatory signal and specific signal. Give the signals for this to occur.
**1st signal of activation:**
TCR binding to cognate peptide:MHC complex
## Footnote
**2nd signal of activation:**
Interaction between CD28 on T cell with B7 (co- stimulator) on APC
36
For the activation of naive T cells, what must be present for this to occur wrt signaling (3 different possibilites)
1. To **activate a T cell**, BOTH a co-stimulatory signal and specific signal must be present
2. If there is only a specific signal alone, **T cell becomes anergic**
3. if co-stimulatory signal alone then there is **no effect on the T cell**
37
Describe how the Co-Stimulator Molecule (B7) Expression is Inducible
1. phagocytosis and breakdown of bacteria by macrophage induces expression of MHC II and B7
2. Macrophage delivers a co-stimulatory signal to T cells recognizing bacterial peptide antigen
3. proliferation and differentiation of T cells specific for bacterial protein
38
Describe non-bacterial protein antigen presentation by macrophages
unstimulated macrophages do NOT deliver a co-stimulatory signal to T cells recognizing a nonbacterial antigen
results =\> anergic T cells
39
Describe bacterial antigen presentation by macrophages
bacteria stimulate macrophages to deliver a co-stimulatory signal to T cells recognizing a bacterial antigen
results=\> **proliferation and differentiation of T cells specific for a bacterial protein**
40
Describe antigen presentation of macrophages when they encounter both bacteria and nonbacterial proteins
bacteria stimulate macrophages to deliver a co-stimulatory signal to T cells recognizing a nonbacterial antigen
results =\> **proliferation and differentiation of T cells specific for a non bacterial protein**
41
Why is there more signaling required to activate naive CD8 T cells?
* important because of the cytotoxic capacity of CTLs
* built-in regulatory fail safe of the immune system
42
Describe the 3 ways for CD8 T cells to be activated
1. DCs expess high levels of B7 and can activate naive CD8 T cells =\> activated CD8 T cell makes IL-2, driving its own proliferation and differentiation
2. APC stimulates effector CD4 T cell, which in turn activates the APC =\> activated APC expresss B7, which co-stimulates naive CD8 T cell
3. APC activates CD4 T cell to make IL-2 and naive CD8 T cell to express IL-2 receptors =\> IL-2 secreted by activated CD4 T cell is bound by CD8 T cell
43
What is an “Armed” Effector T cell? Name 2 important characteristics involved
a fully differentiated T cell that is ready to perform its effector function
* • does not require co-stimulation to perform function
* • express different array of adhesion molecules that direct them to appropriate tissues
44
What are the 3 main types of armed effector T cells?
1. CD8 T cells
2. CD4 Th1 cells
3. CD4 Th2 cells
45
Describe the CD8 effector T cell wrt binding and secretions
Binds to virus infected cell via Fas ligand on it and Fas on the virus
releases cytotoxins and cytokines
46
T cell secretes effector molecules onto surface of target cell. Name the cytotoxins and cytokines secreted from CD8
**Cytotoxins **
* perforin
* granzymes
* granulysin
**Cytokines**
* IFN-y
* LT
47
Describe the CD4 Th1 effector T cell wrt binding and secretions
Th1 bind to macrophage containing bacteria via CD40 ligand on it and CD40 on the macrophage
secretes cytokines in response
48
What are the cytokines secreted by Th1 cells?
* IFN-y
* GM-CSF
* TNF-a
* LT
* IL-3
49
Describe the CD4 Th2 effector T cell wrt binding and secretions
Th2 uses CD40 ligand to bind to CD40 on the B cell presenting specific antigen
Secretes cytokines
50
What are the cytokines secreted by Th2 cells?
* IL-4
* IL-5
* IL-10
* IL-13
* TGF-B
51
Describe the differentiation of helper T cells and function of Th1
1. Naive CD4 T cell
2. proliferating T cell
3. immature effector T cell
4. Th1 cell
* IL-2, IFN-y
* Macrophage activation, B cell activation, and production of opsonizing antibodies such as IgG1
52
Describe the differentiation of helper T cells and function of Th2
1. Naive CD4 T cell
2. proliferating T cell
3. immature effector T cell
4. Th2 cell
* IL-4, IL-5
* General activation of B cells to make Abs
53
What Drives Differentiation of TH0 to TH1/TH2? When does it occur?
**“Decision” made during T cell activation; influenced by pathogen**
1. cytokine environment during activation
2. antigen presented to TH0 cell influences differentiation pathway
54
Describe the cytokine environment during activation wrt Th1 and Th2 cells. What stimulates them to become each?
• CD4 cells activated in presence of IL-12 and IFN-γ will become TH1 cells
## Footnote
• CD4 cells activated in presence of IL-4 and IL-6 will become TH2 cells
55
Antigen presented to TH0 cell influences differentiation pathway. Describe how it influences Th1 and Th2 differentiation
• presentation of low affinity or low concentration of Ag \>\>\>\> TH2
## Footnote
• presentation of high affinity or high concentration of Ag \>\>\>\> TH1
56
Give an example with steps of how Differentiation of TH0 to TH1
1. Viruses and some bacteria induce IL-12 secretion by DCs that can activate NK cells to produce IFN-y
2. Naive CD4 T cells, activated in the presence of IL-12 and IFN-y, are committed to differentiate into Th1 cells
57
Give an example with steps of how Differentiation of TH0 to Th2
1. Other pathogens may cause synthesis and secretion of IL-4 by NK T cells
2. Naive CD4 T cells activated in the presence of IL-4 are committed to differentiate into Th2 cells
58
What is a dedicated population of T cells whose function is to suppress T cell activation?
T regulatory Cells
59
T cells differentiate into T regs when?
during thymic development
60
Describe T regs wrt repertoire, expression and production of cytokines
• have large receptor repertoire that is biased towards self-peptides
## Footnote
* express the transcription factor Foxp3
* produce TGF-β and IL-10
61
What suppresses the activation and development of naive T cells?
T reg cells
62
What is a pro-inflammatory cell type that has important role in anti-microbial immunity at epithelial/mucosal barriers?
Th17 cells
63
Describe the differentiation into Th17 and the cytokine production done by Th17
* differentiation of TH0 into TH17 cells is driven by several cytokines (TGF-β, IL-6, IL-21, and IL-23)
* TH17 cells produce **IL-17 (**neutrophil recruitment/activation) and **IL-22 ** (which stimulates epithelial cells to produce anti-microbial proteins)
64
What role does IL-17 have?
neutrophil recruitment/activation
65
What is the role of IL-22?
stimulates epithelial cells to produce anti-microbial proteins
66
T/F initiation of adaptive immune responses occurs at the sites of infection
false, initiation of adaptive immune responses does not occur at the sites of infection
pathogen- derived antigens are taken by the lymph to secondary lymphoid organs were the antigen is processed and presented (peptides bound to MHC) by professional APCs
67
What type of T cells leave the thymus by entering the bloodstream from which they migrate through the various secondary lymphoid tissues?
mature
68
Describe the process of how naive T cells enter the lymphoid organs?
by crossing the walls of high epithelial venules (HEV);
this process is **mediated by adhesion molecules selectively expressed by naïve T cells**
69
\_\_\_\_\_ is expressed by naïve T cells and binds to carbohydrate moieties of vascular addressins which are \_\_\_\_\_? Where are the vascular addressins expressed?
L-selectin
CD34 and GlyCAM-1 which are expressed on surface of HEVs
70
What allows naive T cells to interact via diapedesis?
L-selectin expressed by naïve T cells and binds to carbohydrate moieties of vascular addressins (CD34 and GlyCAM-1) that are expressed on the surface of HEVs allows for diapedesis
71
What is role of chemokines bound to the surface of HEVs?
activate lymphocyte-function-associated antigen-1 (LFA-1, on the T cell)
72
Describe the step by step process of diapedesis (3)
1) chemokines bound to the surface of HEVs activate lymphocyte-function-associated antigen-1 (LFA-1, on the T cell)
2) LFA-1 then binds tightly to intracellular adhesion molecule-1 (ICAM-1) on the HEV
3) the tight interaction allows the T cell to squeeze between two endothelial cells and enter the
2 ̊ lymphoid tissue (diapedesis)
73
Similar to positive selection of T cells in the thymus, what else is a survival signal for T cells?
contact between naïve T cells and dendritic cells (MHC:self peptides) also appears to act as a
survival signal for the T cell
74
initial interactions between T cells and APC are mediated by what? What is important about these interactions?
cell adhesion molecules
these interactions facilitate interaction of the TCR of the T cell with the MHC complexes on APCs
75
adhesion molecules on the surface of the T cell are \_\_\_(3)\_\_\_ bind to adhesion molecules on the surface of the antigen-presenting cell \_\_\_(3)\_\_\_?
LFA-1, CD2, and ICAM-3
ICAM-1 or 2, LFA-3, and LFA-1)
76
What happens if the T cell encounters its cognate peptide:MHC complex during this interaction (specific antigen recognition)?
LFA-1 on the surface of the T cell undergoes a conformational change that increases its affinity for ICAMs, which prolongs the cell-to-cell contact
77
What happens to naïve T cells that do not encounter specific antigen?
* enter the efferent lymphatic vessel,
* return to the bloodstream,
* recirculate back to other secondary lymphoid tissues
78
each of the different antigen-presenting cells (APCs) are specialized to deal with a particular type of pathogen: name them
1) **dendritic cells** are most efficient at presentation of viral peptide antigens; also able to present antigens derived from the extracellular milieu
2) **macrophages** are best suited for capturing extracellular, independently replicating organisms such as bacteria and yeast; can also present antigens derived from intracellular pathogens
3) **B cells** most efficiently present peptide from soluble antigens; can present antigens derived
from intracellular and extracellular sources
79
What is one feature that distinguishes APCs from all other cells in the body? What is its role?
their ability to express a surface molecule known as co-stimulator molecule, or B7
B7 molecule binds to a T cell surface molecule known as CD28
80
What is the only way for activation of T cells to occur?
only APCs can activate naïve T cells
81
there are two signals that are required for T cell activation: Name them
1) binding of the TCR to its cognate peptide in the context of MHC
2) co-stimulation signaling that results from interaction between B7 (on the APC) and
CD28 (on the T cell)
82
What is the best APC? what is its main role as a cell?
mature dendritic cells are the most potent antigen-presenting cells
their sole function is to present antigen to T cells
83
Describe the path from beginning to end of a dendritic cell (DC) and where specifically they reside
1) common myeloid progenitor =\> immature DC,
2) leave the bone marrow and migrate to their peripheral sites
generally found under most surface epithelia and in solid organs
84
What is the role of immature DC?
immature dendritic cells do not present antigen;
**they are very active in taking up antigen**
85
How do immature DCs generally take up antigen?
macropinocytosis
86
What signals immature DCs to mature? Where does this occur?
immature dendritic cells are **signaled by infection** to migrate (via lymphatics) to the **T cell
zones of secondary lymphoid tissues**where they become mature
87
mature DCs, or interdigitating reticular cells, cannot do what? what is their role?
can no longer take up antigen
now are able to productively present antigen to T cells
88
What 3 things do mature DCs express? Name them specifically
* express co stimulatory molecules (B7) and high levels of MHC I and II
* adhesion molecules (ICAM-1, ICAM-2, LFA-1, and LFA-3)
89
mature DCs produce what and what is the purpose?
produce a chemotactic cytokine (or chemokine) that
attracts naïve T cells;
this chemokines is known as “DC-CK”
90
What is an immature DC of the skin? What is its main role?
Langerhans' cells
uptake of antigen
91
What are scavenger cells that can be induced by pathogens to present antigens to naïve T cells?
macrophages
92
Why are macrophages considered in the front line of defense against microorganisms?
they phagocytose and destroy many microbes without the aid of acquired immune responses
93
T/F resting macrophages do not express MHC class II and do not express B7
false, resting macrophages **express very low levels of MHC class II** and do not express B7
94
What is peripheral tolerance wrt macrophages?
macrophages that encounter antigen in the absence of bacterial products will present antigen
(low level) but will not supply co-stimulation signals to T cells which induces anergy
95
When will a macrophage act as an APC?
macrophages in which microbes persist participate in the development of acquired immunity by
acting as professional antigen presenting cells
96
Once a macrophage uses its numerous receptors for microbes, it uptakes and phagocytosis them. What occurs next?
once phagocytosed, the microbe is processed and the resulting peptides are loaded onto and presented by MHC molecules
97
Once a macrophage phagocytosizes a microbe, what occurs wrt MHC and other molecules??
upregulate their expression of MHC molecules
upregulate expression of B7 molecules
present peptides from the pathogen on MHC molecules
98
What is a unique characteristic that makes B cells a professional APC?
bind to soluble antigenic molecules through their B cell receptors (surface Ig)
99
After binding to soluble antigenic molecules, B cell do what?
B cell internalizes antigen, processes antigen, and presents peptides on MHC class II molecules
100
What T cell does the B cell present to? Why?
since B cells constitutively express high levels of MHC class II molecules, and peptide:MHC complexes are displayed on the cell surface, **B cells readily present antigen to antigen- specific CD4+ T cells**
101
If the B cell presents to a T cell that is an effector cell, what will occur?
expression of B7 is upregulated by microbial products
a B cell that has upregulated B7 expression can productively present peptide antigens to naïve CD4+ T cells (**2nd signal of B cell activation**)
102
What are the 2 signals required for the activation of T cells?
1) encounter with specific peptide antigen bound to an MHC molecule on an APC
2) interaction of CD28 (on the T cell) with B7 expressed on the surface of the APC to lead to upregulation of IL-2
103
What is important about the interaction of CD28 on the T cell with B7 expressed on the APC?
•• this signaling thru CD28 is thought to stabilize IL-2 mRNA (20-30 fold increase in IL-2 expression results);
## Footnote
CD28 signaling also appears to activate the transcriptional activators AP-1 and NF- B (increases IL-2 expression by 3 fold);
**total upregulation of IL-2 is around 90-fold**
104
a T cell that recognizes its specific antigen bound to MHC, but does not receive the co- stimulation signal, will become anergic. What term is this?
peripheral tolerance
105
What affect will costimulation in the absence of specific antigen will have on the T cell? Why is this important?
costimulation in the absence of specific antigen will have ***_no effect_*** on the T cell
helps to prevent autoimmune responsiveness
106
Why CD8+ T cells need more co-stimulation than do CD4+ T cells?
since the effector function of CD8+ T cells is so destructive, the mechanism for activation of these cells is somewhat more stringent
107
What is a require to activate a CD8 T cell?
activated by dendritic cells (DCs they have intrinsically high costimulation activity)
108
If a DC does not present to a CD8, how can other APCs activate it? How specifically?
often requires that both the CD8+ T cell, and a CD4+ T cell must recognize antigen on the same APC simultaneously
## Footnote
CD4=\> 1) induce macrophages to upregulate B7 expression (upregulate costimulation potential) on the macrophage
CD4=\> 2) produce IL-2 which could bind to IL-2 receptors on the CD8 cell
109
the proliferation and differentiation of activated T cells is driven by what molecule?
autocrine growth factor, interleukin-2 (IL-2)
110
What is the role of IL-2 production and responsiveness in T cell activation? (3)
1. IL-2 is produced by activated T cells upon activation
2. T cells normally express a moderate affinity form of IL-2 receptor, allowing T cells to respond only to high [IL-2]; activation of T cell induces expression of a high affinity form of the IL-2 receptor which allows T cells to respond to lower [IL-2]
3. after proper activation signals and binding to IL-2 thru its high affinity IL-2 receptor, cell can divide 2-3x/day for several days
4. IL-2 also stimulates differentiation of these new cells into armed effector cells
111
What is the structure of the IL-2 receptor?
* the high affinity IL-2 receptor is a heterotrimer and consists of an alpha, beta, and gamma chain =\> **all 3 traverse membrane of T cell**
* the moderate affinity IL-2 receptor is composed of only the Beta and gamma chains
112
What is a T cell that can produce all of the proteins that are required for its specialized function?
an armed T cell effector cell
113
What are the 3 most important characteristics of armed effector T cells?
1. **armed effector T cells can become activated to perform their function by stimulation with specific antigen alone**; **no costimulation signal is needed (B7:CD28 signaling is not required)**
2. they express higher levels of the adhesion molecules LFA-1 and CD2, but lose cell-surface L- selectin (no longer recirculate through lymph nodes)
3. they express VLA-4 (adhesion molecule) which allows them to bind to vascular epithelium at sites of inflammation (promotes movement into infection site)
114
When do activated T cells differentiate into effector T cells?
1. once a naïve T cell receives the two signals required for activation, it secretes and responds to IL-2 which drives rapid proliferation of the particular T cell clonal line
2. **after 4-5 days of rapid proliferation, the newly generated cells then differentiate into effector cells that are able to respond to antigen without co-stimulation**
115
What are the 3 primary classes of effector T cells?
1. Effector CD8 T cells
2. Th1 CD4 cells
3. Th2 CD4 cells
116
Each class of effector T cells are specialized to deal with different types of pathogens. Describe effector CD8 T cells
cytotoxic T cells
* recognize peptide antigens bound to MHC class I molecules presented on the surface of infected cells;
* could be any nucleated cell in the body that is infected with a virus or intracellular bacteria or parasite;
* CTLs kill these cells
117
Each class of effector T cells are specialized to deal with different types of pathogens. Describe Th1 CD4
* primarily involved in development of cell-mediated immune responses
* recognize peptide antigens bound to MHC class II molecules presented on the surface of macs or B cells
118
Each class of effector T cells are specialized to deal with different types of pathogens. Describe Th2 CD4
* primarily involved in development of humoral immune responses
* recognize peptide antigens bound to MHC class II molecules presented on the surface of B cells (primarily)
119
in general, TH1 CD4 T cells produce cytokines that modulate the function of the APC that is
presenting the antigen to the CD4 T cell. Describe this in detail wrt to macs and B cells
* TH1 cells supply helper signals (cytokines) that stimulate macrophages, making them more phagocytic and more bacteriocidal
* supply help (in the form of cytokines) to B cells (2nd signal of activation)
* influences class switching and initiates somatic hypermutation
* **TH1 CD4 cells induce B cells to produce Ab (class switching) that are efficient for opsonization (IgG1 and IgG3)**
120
T/F Th2 CD4 cells supply help to B cells that can influence class switching and initiate somatic hypermutation
true
121
T/F TH2 CD4 cells induce B cells to produce all other isotypes of Ab
true
122
T/F Naïve CD8 cells emerging from the thymus are destined to become CTL
true
123
How is it decided whether a T helper Cell will be a TH1 or TH2 cell?
all CD4 cells that leave the thymus
are considered TH0 cells
the decision to become a TH1 or a TH2 cell is made upon 1st encounter with antigen
124
Why is the decision between Th1 and Th2 development vital?
it determines whether the acquired immune response will be primarily cell-mediated or Ab-mediated
125
What are the factors that contribute to the decision bw Th1 and Th2 development?
1. cytokine environment upon initial activation of a naïve T cell
2. the “nature” and amount of antigen presented to a naïve TH0 cell also influences differentiation into either a TH1 or TH2 cell
126
WRT the “nature” and amount of antigen presented to a naïve TH0 cell also influences differentiation into either a TH1 or TH2 cell. Describe this in wrt concentration of the antigen
* TH0 cells that are presented with **low concentrations** of antigen that bind **weakly to the TCR** tend to differentiate into **TH2 cells**
* TH0 cells that are presented with **high concentrations** of antigen that **bind tightly to the TCR** tend to differentiate into **TH1 cells**
127
WRT cytokine environment upon initial activation of a naïve T cell. Describe the environment that will lead to Th1 cells. Give details of the cytokines as well
presence of IL-12 and IFN-y =\> Th1
IL-12 is produced by macrophages and dendritic cells in response to viral and some intracellular bacterial infections
NK cells and T cells produce IFN-y which inhibits development of Th2 cells
Th1 cells produce IFN-y which down-regulates proliferation of Th2
128
WRT cytokine environment upon initial activation of a naïve T cell. Describe the environment that will lead to Th2 cells. Give details of the cytokines as well
presence of IL-4 and IL-6 tend to differentiate into Th2 cells
•• IL-4 and IL-10(produced by Th2) inhibit the generation of TH1 cells
a possible source of IL-4 is a subset of CD4 T cells known as NK1.1+ CD4 T cells or NK T cells
129
What is a T reg cell?
CD4+ T cells that have these characteristics:
1) self antigen-specific T cell receptors,
2) express a surface protein known as CD25
3) express a transcriptional repressor known as FoxP3.
130
TH0 cells differentiate into Treg cells when they are activated in the presence of what?
TGF-B
131
How are T regs used in the active peripheral tolerance mechanism?
upon recognition of their cognate self antigen, Tregs produce mediators (cytokines) that suppress proliferation of naïve T cells that are responding to self-antigens presented on the same APC
132
Why does the deficiency of FoxP3 (an X-linked gene) produce a fatal autoimmune disease directed at a variety of host tissues? What is the only treatement for this disease known as IPEX?
Since FoxP3 is a transcriptional repressor, the Treg will not be able to cause apoptosis to the self-antigen specific TCR thus causing these cells to remain alive and attack the body
Tx=\> bone marrow transplant from healthy HLA-identical sibling
133
What is a newly discovered subset of T helper cells that produce interleukin-17 (IL-17), IL- 21, and IL-22?
Th17 cells
134
deficiency of TH17 cells can leave the patient susceptible what?
susceptible to opportunistic pathogens
135
What is a newly discovered subset of helper T cells that produce TGF-B and IL-10?
Th3 cells
