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M1 – Immunology
EFFECTOR T CELL FUNCTIONS
(Part I)
March 27, 2009
Ronald B. Smeltz, Ph.D.
Microbiology and Immunology
[email protected]
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Summary: Cytokines and chemokines
1. Cells make cytokines, which are proteins that cause a biological effect when they bind to target cells that
express the appropriate cytokine receptor
2. Cytokine receptors consist of homo- and heterodimers, as well as homotrimers
3. The common gamma chain receptor is critical for normal development and maintenance of lymphocytes
4. Cytokine receptors utilize the Jak-Stat pathway, which involves dimerization of the cytokine receptor and a
series of phosphorylation events that lead to gene transcription in the target cell
5. The common gamma chain cytokines IL-2, IL-7, and IL-15 promote T cell growth/ survival
6. IL-12, IFN-a/b, IFN-g, and TNF-a constitute pro-inflammatory cytokines
IL-12 induces IFN-g
IFN-g has macrophage-activating properties critical for eliminating intracellular infections
IFN-g is the major cytokine produced by Th1 cells
7. TGF-b and IL-10 constitute anti-inflammatory cytokines
Lack of TGF-b or IL-10 leads to severe inflammation/autoimmune disease
Regulatory T cells can express TGF-b and suppress T cell responses
8. Chemokines are a special group of chemoattractant cytokines that recruit cells into tissues
9. Chemokine receptors consist of a 7-transmembrane-spanning region, and are G-protein-coupled receptors
Learning objectives
1. Identify the two main categories of effector T cells
2. Recognize the different subsets of effector CD4+ T cells
3. Distinguish the functions of effector CD4+ T cells
4. Determine the effector functions appropriate for T cell responses
to an intracellular bacteria, extracellular bacteria, helminth, and
a virus
5. List the effector molecules of CD8+ cytotoxic T cells
6. Describe the mode of action for granzymes
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I. Definition of an effector function
• Effector functions are the physiological and cellular process
used by the immune system to eliminate pathogens from the
body.
• Effector functions are in the form of cytokines, chemokines
and cytotoxins (cytotoxic cytokines).
Cytokines
Cytokines--> Naïve T cells-->Effector T cells Chemokines
Cytotoxins
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II. The types of effector cells
•
The two types of effector T cells in the immune system are
helper T cells and cytotoxic T cells
1. Cytotoxic T cells (CD8+) express cytokines and
cytotoxins and are specialized for killing of infected
cells, tumor cells, or MHC-mismatched cells
2. T helper cells (CD4+) are heterogeneous and
distinguished by their cytokine secretion profiles
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II. The types of effector cells
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II. The types of effector cells
a. Th1 cells secrete IFN-gTNF-a
 promote MACROPHAGE-mediated immunity
 Th1 cells can help B cells make antibody
b. Th2 cells secrete IL-4, IL-10, IL-13
 promote EOSINOPHIL-mediated responses
 Th2 cells can help B cells make antibody, especially IgE
c. Th17 cells secrete IL-17
• promote NEUTROPHIL-mediated responses
d. Treg cells express TGF-b and/or IL-10 and suppress T cell
responses
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III. The effector functions of cytotoxic and
helper T cells
What effector T cells are specialized for intracellular infections?
How do their effector mechanisms differ?
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IV. General properties of effector T cells
1. Increased migration to non-lymphoid tissues
2. Highly specialized to produce effector molecules
3. Shorter time required for activation
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V. CYTOTOXIC T CELLS
• Differentiation of naïve CD8+ T cells into effector cytotoxic T
cells requires the synthesis of proteins that become part of the
lytic granule, a specialized intracellular compartment:
1.Perforin
2.Granulysin
3.Granzymes
4.Calreticulin
5.Serglycin
6.Cathepsins
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V. CYTOTOXIC T CELLS
• The effector molecules of cytotoxic T cells:
1.Perforin (cytotoxin)
2.Granzymes (cytotoxin)
3.Fas-L
4.TNF-a/b
5.IFN-g
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V. CYTOTOXIC T CELLS
•
Binding of the activated, cytotoxic effector cell to an infected
target cell leads to formation of an immunological synapse:
1. Effector T cell binds to target cell
•
LFA-1/ICAM-1 interactions increase binding between
effector and target cell.
2. Movement of lytic granules toward the target cell.
3. Release and entry of granules into infected cell
4. Apoptosis of infected cell.
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V. CYTOTOXIC T CELLS
The formation of the
immunological synapse
and polarized release of
lytic granules
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V. CYTOTOXIC T CELLS
Apoptosis, also called programmed cell death, is the
process by which a cell self-destructs because of the
activation of enzymes that degrade its own DNA.
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VI. Mode of action of perforin and
granzymes
Perforin:
• Forms polymers and creates “holes” in the cell membrane.
Disrupts the cell membrane of the infected cell, increasing
permeability to water and calcium (pore-forming)
• Granzyme B:
 Activates caspases
 Caspases then activate DNases
 DNases degrade DNA
• Apoptosis of target cell
• Not all granzymes use caspases, however
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