32 T cells Flashcards
This form of T cell activation generates a diverse repertoire of mature T cells
Antigen independent activation
This form of T cell activation results in:
1) Activation (two signals: MHC complex + B7 binding or IL-2R activation)
2) Survival
3) Proliferation (clonal selection)
4) Differentiation into effector T cell or Memory T cell (always ready to switch to an effector T cell)
Antigen dependent activation
This type of T cell activation leads to apoptosis or anergy
TCR-MHC2 binding only
This type of T cell activation leads to proliferation, differentiation, and effector function
MHC2-TCR and CD28-B7 (CD80/86)
This type of T cell activation leads to cell-cycle arrest
MHC-TCR and (CTLA-4)-B7(CD80/86)
: IL-2 release from the CD4+ cell is a(n) ___ signal that binds to the IL-2 receptor and signals proliferation and activation.
Autocrine signal. Note: This is why experienced T cells have a lower threshold for activation (they already have many IL-2 receptors in the membrane)
binds to B7 by displacing CD28, blocking IL-2 synthesis. As a result, the antigen presenting cell becomes less effective at presenting antigens to T cells, and T cell activation is inhibited (anergy is the major outcome of this)
Cytotoxic lymphocyte antigen-4 (CTLA-4)
Naïve T cells circulate through the lymph nodes and find antigens
Activation of naïve T cells in the lymph nodes leads to development of effector cells, and clonal expansion
These experienced T cells now have no business in the lymph nodes, and migrate to the site of infection (or other lymph nodes to meet B cells)
Antigen presentation to experienced T cells: At the site of infection, macrophages and B cells present the antigen to experienced T cells, telling the T cells that their presence is indeed necessary there to help eliminate the infection. If the innate immune system has cleared the infection, no such signal will be received and the T cell will die
Activation and migration of T cells
T cells that have not divided into a specific subtype
Naive helper T cells (Th0)
subtype of T cell that is responsible for helping B cells produce antibodies (as well as assisting w/ class switching). Located in the follicles (w/ the B cells)
Follicular helper T cells
Subtype of T cell that activates macrophages to deal w/ intracellular infections
Effector helper T cells (Th1)
Subtype of T cell that activates neutrophils and induces inflammation
Effector helper T cells (Th17)
Subtype of T cell that induces production of IgE to deal w/ parasitic infections
Effector helper T cells (Th2)
Cytokines that cause Th0 cells to differentiate into Tfh cells
IL-6 and IL-21
This cell gives the 2nd signal to the B cell to differentiate and produce antibodies (remember that the 1st signal is antigen phagocytosis)
Follicular helper T cells
This cell type mainly deals w/ intracellular infections. I.e. microorganisms that evade the immune response and establish infections (ex: bacteria that prevent fusion of the phagosome w/ the lysosome)
Th1 cells
T/F
• A macrophage gets infected w/ a bacteria, and is unable to clear the bacteria from its cytosol.
• A dendritic cell now migrates to the lymph nodes and presents the antigen of this intracellular pathogen to a Th0 cell, which differentiates into a Th1 cell.
• The Th1 cell now secretes IFN-gamma (main secretion of these cells), which enhances the ability of macrophages to destroy the intracellular pathogen
True
This cell type secretes IFN-gamma and helps the B cell to produce a particular type of IgE molecule (which is good at fixing complement, neutralizing the antigen, and activating macrophages). Only effective against extracellular pathogens
Th1 cell (secondary function)
IL-2, TNF-alpha, and IFN-gamma are the major secretions of which cell type?
Th1 cells
Th0 cells differentiate into Th1 cells in response to which cytokine? What cell type releases this cytokine?
IL-12. Released by activated macrophages
This cell type makes macrophages better at killing microbes and better at presenting antigens (in case it cannot clear the infection, it can recruit help from CD8+ cells)
Th1 cells
Signaling from which cytokine released from which cell type(s) results in differentiation into Th2 cells?
IL-4. Released by APCs
The major function of this cell type is stimulating production of IgE
Th2 cells
T/F. IL-4 secretion from Th2 cells induces B cells to produce IgM, which binds to a parasite and induces degranulation of mast cells –killing the parasite
False. . IL-4 secretion from Th2 cells induces B cells to produce IgE, which binds to a parasite and induces degranulation of mast cells –killing the parasite
IL-4, IL-13, and IL5 are cytokines secreted by which cell type and what is their function?
They are secretions of the Th2 cell type. Their function is to attract cells that can bind IgE (granulocytes and mast cells) and increase intestinal motility. These are anti-parasite defenses
The major cytokine of this cell type is IL-4. Promotes differentiation of Th0 into Th2 cells. Promotes switch to IgE (and IgG) production to deal w/ parasites. Responsible for allergic reactions. Inhibits Th1 production from Th0
Th2 cell type
T/F. Th2 cells mediate the response against intracellular infections
False. Th2 cells mediate the response against parasites
Which cell type secretes IL-17 and IL-22?
Th17 cells
This cytokineattracts neutrophils to the site of inflammation by inducing the cells of the infected tissue to secrete the inflammatory cytokines (promoting inflammation). Also increases the production of anti-microbial peptides from epithelial cells
IL-17
This cytokine activates cytotoxic T lymphocytes, inducing cell death by apoptosis
IL-2
T/F. A dendritic cell must migrate from the site of infection to the lymph node to present the antigen to the T cell.
1) In this case, the first thing that the dendritic cell must do is present the antigen to a naïve T helper cell.
2) The T helper cell then activates the CD8+ cell
3) Two signals for activation: 1st signal from antigen, 2nd signal from T helper cell. Both are necessary for activation (which stimulates survival, proliferation, and differentiation)
4) The CD8+ cell then differentiates into memory T cells and Cytotoxic T lymphocytes (CTLs)
True
T/F. Naïve CD8+ cells emerge from the thymus. Activation requires recognition of the cognate antigen-MHC by TCR and proper co-stimulatory signals (directly by APC or Th cell)
True
o Perforin/granzyme-mediated cell killing: Perforin pokes hole in the membrane. Granzyme is then injected into the cell. Granzyme activates caspases, activating apoptosis
o Fas/Fas ligand mediated cell killing: The FasL on CTL surface interacts w/ the Fas receptor on the target cell, initiating the intrinsic pathway of apoptosis.
Mechanisms of cell death induced by cytotoxic T cells
Defects in this cell type result in increased susceptibility to viral and intracellular bacterial infections and reactivation of latent virus infections (such as infection by the epstein-barr virus), which are normally kept in check by these cells
Cytotoxic T lymphocytes
___ reactions are mediated by Th1 cells
Delayed type hypersensitivity reactions
The classic inflammatory cytokines that function to recruit phagocytic cells to the site of infection
TNF-alpha & IL-1
Certain B cells release this Ig isotype. The function is neutralization of the effect of the pathogen
IgG4
Review diagrams
Do it
Cytokines secreted by macrophages
TNF, IL-1, and IL-12
This cell type enhances the killing capability of macrophages by increasing the rate of production of ROSs (ex: NO) and lysosomal enzymes
Th1 cells
This cell type causes the macrophage to increase secretion of cytokines (TNF, IL-1, and IL12) and chemokines
Th1 cells
This cell type causes the macrophage to increase expression of B7 and MHC in their membranes
Th1 cells
