Chapter 8: T Cell-Mediated Immunity Flashcards
Two Stages of T Cell Mediated Immunity
- T-cell priming
- Effector function
Who activates cells
- immature dendritic cells (Langerhans cells) take up antigen and migrate to a lymph node
- in lymph node they settle in the T cell areas and differentiate into mature dendritic cells with long fingers (dendrites)
Dendritic cells change their function during their journey to the lymph node. T or F
- T
- immature dendritic cells are good at antigen up-take at the site of infection and mature dendritic cells are good at presenting to T cells in the lymph node
Dendritic cells are adept and versatile at processing antigen from pathogens. Use several pathways to process and present antigens.
- uptake of antigens by phagocytosis which delivers antigen to endocytic vesciles for presentation by MHC class 2 molecules to CD4 T cells
- Viral infection of the dendritic cell delivers peptides processed in the cytosol to the ER for presentation by MHC class 1 molecules to CD8 T cells
- cross presentation of antigen between MHC 1 and 2 (poorly understood)
- antigens tale up on by one dendritic cell can be delivered to a second dendritic cell for presentation by MHC class 1 molecules to CD8 T cells
Naive T cells first encounter antigen presented by ___________ cells in ______________ lymphoid tissues.
- dendritic
- secondary
- naive T cells encounter antigen during their recirculation through secondary lymphoid organs
- they leave the blood at high endothelial venules and enter the lymph-nod cortex, where they mingle with professional APC
Who are the professional APC?
- dendritic cells, macrophages, and B-cells in that order
T cells that do not encounter their specific antigen….
- leave the lymph node in the efferent lymph and eventually rejoin the bloodstream
T cells that encounter antigen on APC…
- are activated to proliferated and differentiate into effector cells
Effector cells can also leave the lymph node in the…
- efferent lymph and enter the cirsulation
Naive T cells can enter lymph nodes int he afferent lymph as well as from the blood. T or F
- T
Recirculation of the T cells can occur through two different ways.
- the blood
- through the lymphatic system
Activation of naive T cells requires a co-stimulatory signal delivered by the 3 kinds of professional APC found in the secondary lymphoid tissues
- principle co-stimulatory molecules on professional APC are B7 molecules, which bind CD28 proteins on the T-cell surface
- binding of TCR and co-receptor CD4 to the peptide occurs
- this signals clonal expansion of T cells only when the co-stimulatory signal is given by the binding of CD28 to B7
- both CD28 and B7 are members of the immunoglobulin superfamily
- microbial substances induce co-stimulatory activity in macrophages
- in absence of infection, macrophages express no B7 and few MHC molecules
3 types of professional APC populate different parts of the…
- lymph node
- dendritic are situated in the T cell areas of the lymph-node cortex
- macrophages are distributed throughout the lymph node
- B cells populate mainly the follicles
Proliferation and differentiation of activated T cells are driven by the cytokine _________
- IL-2
- activation by a APC initiates a program of differentiation in the T cell that starts w/ burst of cell division and then leads to the acquisition of effector function
- IL-2 controls this and is synthesizes by the activation of T-cell itself
Antigen recognition by a naive T cell in the absence of co-stimulation leads to the T cell becoming nonresponsive. Otherwise called…
- Peripheral tolerance
- (anergic)
T-cell tolerance to antigens expressed on nonprofessional APC results from antigen recognition in the absence of co-stimulation. T or F
- T
On activation, CD4 T cells acquire distinctive helper functions. There are two types of helper cells:
- Th1: drives cellular mediated immunity
- Th2: drives humoral immunity
- third type of CD4 T cell: regulatory T cell (Treg): regulated Th1 and Th2
Naive CD8 T cells are activated to become cytotoxic effector cells in several different ways
- activation of naive CD8 T cells to become cytotoxic effector cells (CTL- cytotoxic T lymphocyte) which generally requires stronger co-stimulatory activity than is needed to activate CD4 T cells
- only dendritic cells, the most potent of the APC, provide sufficient co-stimulation
- when APC offers suboptimal stimulation, CD4 T-helper 1 cells can help out to activate naive CD8 T cells
- activity of IL-2 in the proliferation and differentiation of CD8 T cells to effector cells
Effector T-cells responses to infection do not depend on ____________________ signals
- co-stimulatory
- unlike naive T cells, effector T cells can respond without the need for co-stimulatory molecules
- most human cells don’t express the B7 co-stimulatory molecule
- means CD8 cytotoxic T cells can kill any virus-infected cell because of this relaxation in requirement
Effector T-cell functions are carried out by ____________ and _____________
- cytokines
- cytotoxins
- the effector T cell produce distinct sets of effector molecules
Cytotoxic CD8 T cells are selective and serial killers of target cells at sites of infection
- when cytotoxic T cells recognize specific antigen, the delivery of cytotoxins is aimed directly at the target cell
- effector cytotoxic T cells contain stored lytic granules, which are modified lysosomes contain a mixture of specialized protein called cytotoxins
1. Granzymes, perforins, granulysin, and serglycin
2. Producing the Fas ligand
Cytotoxic T cells (CD8 T cells) kill their target cells by inducing apoptosis by 2 methods
- lytic granules
Th1 CD4 cells induce ____________ to become activated
- macrophages
- principle function of Th1 cells is to help the resident macrophages at the sites of infections become more proficient in the phagocytosis nd killing pathogens
- Th1 cells leave the secondary lymphoid tissue to do this (activate macrophages)
Macrophages needed to signals for activation from TH1 cells
- TNF-gamma and CD40 ligand
- TH1 cells coordinate the host response to pathogens that live in macrophages
