1. M1 – Immunology EFFECTOR T CELL FUNCTIONS (Part I) March 27, 2009 Ronald B. Smeltz, Ph.D. Microbiology and Immunology

2. 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

3. 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

4. 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
Chemokines
Cytotoxins
Cytokines--> Naïve T cells-->Effector T cells

5. 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
Cytotoxic T cells (CD8+) express cytokines and cytotoxins and are specialized for killing of infected cells, tumor cells, or MHC-mismatched cells
T helper cells (CD4+) are heterogeneous and distinguished by their cytokine secretion profiles

6. II. The types of effector cells

7. II. The types of effector cells
a. Th1 cells secrete IFN-TNF-
 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
Th17 cells secrete IL-17
promote NEUTROPHIL-mediated responses
Treg cells express TGF- and/or IL-10 and suppress T cell responses

8. 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?

9. 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

10. 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

11. V. CYTOTOXIC T CELLS The effector molecules of cytotoxic T cells:
1. Perforin (cytotoxin)
2. Granzymes (cytotoxin)
3. Fas-L
4. TNF-/
5. IFN-

12. V. CYTOTOXIC T CELLS
Binding of the activated, cytotoxic effector cell to an infected target cell leads to formation of an immunological synapse:
Effector T cell binds to target cell
LFA-1/ICAM-1 interactions increase binding between effector and target cell.
Movement of lytic granules toward the target cell.
Release and entry of granules into infected cell
Apoptosis of infected cell.

13. V. CYTOTOXIC T CELLS
The formation of the immunological synapse and polarized release of lytic granules

14. 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.

15. VI. Mode of action of perforin and granzymes
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