Immune System - Lecture 3 Part B Flashcards
What are Naive T cells stimulated by?
Antigen presenting cells in lymphoid organs
What happens once antigen T cells are stimulated by antigen presenting cells in lymphoid organs?
The T cells will differentiate into effector cells
What are the Effector T cells?
T Helper cells and T Cytotoxic cells
What are the two places that T cells are presented with antigens?
First in the lymphoid tissue then at the site of infection
How do T cells respond to their first encounter with an antigen?
By activating and proliferating and differentiating into effector cells
What are the different methods that CD4 and CD8 cells use to kill pathogens?
- CD4+ secrete cytokines that recruit and activate WBCs to kill the pathogen
- CD8+ lymphocytes kill the infected cells directly
Why is it expected to have many different types of T helper cells?
Because pathogens are very diverse it would be expected that we have many different T helper cells to respond to them
What do the different helper T cells secrete?
Different Cytokines
What are T helper I cells induced by?
Pathogens that are ingested by antigen presenting cells
How do T Helper I cells kill pathogens?
They release cytokines the stimulate phagocyte mediated killing of the ingested pathogen by macrophages
What cytokine is released by Helper T I cells?
Interferon gamma, the most potent macrophage activating cytokine
When are T helper II cells induced?
During parasitic worm infections
What do T helper II cells promote?
IgE production (an antibody)
What does the promotion of IgE production T helper II cells do?
Cause degranulation of mast cells and eosinophils to mediate the destruction of the parasite
Why do T Helper II cells cause degranulation through IgE production as opposed to stimulating phagocytosis?
Because parasites like worms are too large to ingest using macrophages
How do T helper II cells eliminate a worms?
They release cytokines that stimulate B cells to differentiate into plasma cells and produce IgE antibodies that coat the worms and serve as a binding source for mast cells and eosinophils
What do T helper II cells do in addition causing degranulation of mast cells and eosinophils?
They stimulate the production of mucus and intestinal peristalsis to eliminate killed worms from the body
When are T Helper 17 cells active?
During bacterial and fungal infections
How do Helper T 17 cells destroy extracellular pathogens?
They induce inflammatory reactions by secreting cytokines
What do the Cytokine released by T helper 17 cells do?
Stimulate the production of chemokines from other cells which recruit WBCs
What do T Helper cells do in addition to stimulating the production of chemokines?
They maintain the integrity of our epithelial barriers promoting repair of damaged epithelial cells and stimulating the production of endogenous microbial substances
What is the difference between inflammation stimulated by the innate response than by the adaptive response?
The response generated by the Helper T 17 cells is stronger and more prolonged than the innate response
What do T Reg cells do?
They inhibit the proliferation other T cells populations inhibiting the overactive immune responses
What two goals does the Cytokine Interleukin II do for T cells?
- Stimulates T cell proliferation
* Inhibits the immune response by maintaining the survival or regulatory T cells
What are the four main mechanisms that allow T Reg to work?
- Consuming interleukin II
- Produce inhibitory cytokines
- Block co-stimulation
- Causing cytotoxicity
How does the consumption Interleukin II by T Reg cells inhibit the activity of other T cells?
Interleukin II is an essential cytokine for activation of T cell, when T Reg cells consume them they prevent other T cells from becoming activated
How do the inhibitory cytokines produced by T Reg cells affect other T cells?
The inhibitory cytokines prevent other T cells effector mechanisms, preventing them from working
How does the blocking of costimulation by T Reg cells affect other cells?
Costimulation is necessary for activation of T cells, if they do not undergo costimulation then they are unable to activate
How does T Reg cells inducing cytotoxicity affect other cells?
By inducing T cell death they can prevent a T cell from becoming activated
What are Intracellular Pathogens?
Pathogens that directly enter the cytoplasm such as a virus
Why do Intracellular pathogens need to be eliminated by C cytotoxic cells (CD8+ lymphocytes)?
Because they are usually resistant to the antimicrobial mechanisms of T helper cells
What do Intracellular pathogens need to be eliminated by?
T Cytotoxic cells (CD8+ lymphocytes)
What class of MHC do CD8+ lymphocytes recognize?
MHC class I molecules
What does the antigen recognition of MHC I molecules by T cytotoxic cells do?
Cause the activation of signal transduction that will lead to exocytosis of their granules killing by apoptosis
How do T cytotoxic cells kill infected cells?
By inducing Apoptosis
What are the two mechanisms used by T cytotoxic cells to induce apoptosis in cells infested by intracellular pathogens?
- Granule release
* Fas/FasL
What do both Granule release and Fas/FasL by T cytotoxic cells induce?
Apoptosis
How does Degranulation by T Cytotoxic cells work?
The T cytotoxic cell will recognize the MHC antigen and once activated will form a cell and target cell conjugate (kiss of death). They cytoplasm of the cells rearrange causing the golgi and granules to the point of contact, facilitating the granule release directly into the target cells. The granules cause apoptosis and the infected cell dies and the T cytotoxic cell disassociate from the cell that is dying
What do the granules released by T Cytotoxic cells contain?
Perforin and Granzyme B
What does the Perforin released by the Granules of T Cytotoxic cells do?
Form pores that allow the entrance of granzyme
How does Granzyme enter the a cell after Perforin has caused pores?
By the pores via endocytosis
What do Granzymes do once they enter the cell?
They will activate apoptotic pathways by activating cas[ases that induce apoptosis which will lead to DNA fragmentation killing the pathogen and the infected cell
What is FAS?
A transmembrane protein that is expressed by tumors or infected cells
What occurs once FAS links with the FAS ligand on the T Cytotoxic cells?
It will send a signal for apoptosis to occur
What is the difference between Natural Killer cells and CD8+ lymphocytes?
Natural killer cells do not have specific receptors and are part of the innate response
Which cell is the mechanism of natural killer cells similar to?
CD8+ cells
What is the Cytotoxic activity of NK cells stimulated by?
Cytokines during the early infection phase
Which cells are important for controlling an infection during the first seven days and why?
NK cells because T and B lymphocytes need time to develop into effector cells
When does the peak of Natural Killer cells occur?
Before the specific antigen response
What do NK cells release in addition to cytotoxic mediators?
Proinflammatory cytokines, and interferons which activate macrophages
Why are NK cells considered to be part of the Innate system?
Because they lack specific receptors and do not generate memory
How do NK cells kill?
By inducing apoptosis
What is the Cytotoxic mechanism of NK cells?
Using Granzymes and Perforin or by FAS
