Effector T lympocytes Flashcards
Define Naive T cell?
Mature recirculating T cells that have not yet encountered antigen
Define Effector T Cells?
Encountered antigen, Proliferated and differentiated into cells that participate in host defence
Define Memory T cells?
Encountered Antigen, contracted, ready to respond to future infections
Define Target cells?
Cells on which effector T cells act.
When is T cell mediated immunity required?
When pathogens are intracellular- hidden in the cell (TB,Malaria,HIV ect) When organisms evolve to escape antibody recognition- either by changing shape (influenza) or by coating antigen in carbohydrate (HIV) or producing decoy antigens (RSV) Sometimes antibody is insufficient
Why are APC’s important in the induction of T lymphocyte responses?
T cells are only activated by fragments of antigens (peptides) presented in the context of MHC molecules
Where do dendritic cells mature and present antigen on mhc?
lymph node
Lympocytes recirculate from……. and ……. to ……….. ………
Lymphocytes recirculate from blood and lymph to lymphoid organs.
Summarise the effector functions of CD8 + effector T cells?
CD8+ effector T cells destroy target cells such as virus infected cells or tumours Recognise MHCI: Peptide Complexes Effector CTLs secrete granules
Summarise the effector function of Cytotoxic T cells?
CTLs kill their targets by apoptosis
What do CTLS store in their granules?
Perforin and granzymes
What is the function of perforin?
Perforin molecules polymerise and form poers in the target cell membrane
What is the function of granzymes?
They induce programmed cell death in the target cell, thus eliminating cells that have become cancerous or are infected with viruses or bacteria.
What happens after CTLs recognise infected targets?
granules are released
Summarise the effector function of T lymphocytes including cell-mediated cytotoxicity
• Cytotoxic T cells (CTL) kill their targets by programmed cell death = apoptosis • Apoptosis is characterized by fragmentation of nuclear DNA • CTL store perforin, granzymes, granulysin in cytotoxic granules • granules are released after target recognition • perforin molecules polymerise, form pores • FasL (on CD8) can induce cell death by interacting with Fas on target cells
What does Fas-FasL interaction induce?
apoptosis
What type of cell activates Macrophages to promote killing of intracellular pathogens?
CD4+ Th1 effector cells
What does Th1 stand for?
T helper 1 cells
T helpers are defined by the cytokines they produce and the transcription factors they use True or false
True
What does Th1 cells boost?
Boost intracellular immune response
What does TH1 produce?
Produce interferon gamma
What do activated macrophages express and release?
They express increased levels of CD40 and TNF-alpha receptors Secrete TNF-alpha
Activated macrophages express increased levels of CD40 and TNF-a receptors, and secrete ……. which synergises with …….. in the induction of antimicrobial effector mechanisms.
TNF-alpha and IFN-gamma
What is the primary role of delayed type hypersensitivity?
primary role in defence against intracellular pathogens
What induces DTH?
Intracellular parasites Intracellular bacteria Intracellular fungi Intracellular Viruses (herpes)
What does the DTH produce if the antigen is not a microbe, like in contact hypersensitivity?
the DTH produces tissue injury without protection = “hypersensitivity”
How long, after antigen exposure, does local swelling with cellular infiltrates occur?
24-72 hours
What happens if the source of antigen is not eradicated in DTH?
Chronic stimulation, granuloma formation
What type of cells are involved in DHC?
Th2 and Th1 cells
What do Th1 cells release in DHC?
Chemokines Cytokines (IFN-gamma) Cytotoxins Release inflammatory cytokines that affect blood vessels (TNF-beta)
Name 2 pathological reactions caused by T cells?
Autoimmunity - antigenic peptide derived from self protein Rejection (transplants) - antigenic peptide derived from self protein of transplant donor
What is the function of CD4+ Th1 effector cells?
Activate infected macrophages which present peptides in context with MHC class II molecules on their cell surface. Activate CD8 T cells
What is the function of CD4+ Th2 effector cells?
They are also MHC class II restricted and help B cells differentiate into antibody secreting plasma cells.
Boost anti-multicellular organism response
What is the function of Th17 cells?
produce a particular set of inflammatory cytokines They are also protective against some bacterial infections and also mediate pathogenic responses in autoimmune diseases
What is the function of Regulatory T-cells (Treg) cells?
Inhibit the activation of of naive and effector T cells by contact dependant mechanism or by secreted cytokines
T cells that regulate the activation or effector functions of other T cells
natural and induced regulatory T cells
necessary to maintain tolerance to self antigens
The regulatory T cells (Tregs /ˈtiːrɛɡ/), formerly known as suppressor T cells, are a subpopulation of T cells that modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. Tregs are immunosuppressive and generally suppress or downregulate induction and proliferation of effector T cells.[1]
When are effector T cells activated?
Helper T cells become activated when they are presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presenting cells (APCs). Once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response.
