4-cell mediated immunity
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Cell Mediated Immunity
Dr. Anita Devi K Ravindran
MBBS, MD, Dip Cert Med Edn
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Learning Objectives
At the end of the session, the student should be able to
Differentiate between the cells and their role inhumoral and cellular immunity.
Describe the various classes of T cells and their roles. Enumerate the antigen presenting cells and their role
in relation to MHC molecules.
Describe the structure and role of T cell receptor,
adhesion molecules and co-stimulatory molecules Explain the role of IL 2 in T cell proliferation and action.
Discuss the homeostasis mechanisms which regulate Tcell activity.
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Cell mediated immunity
Mediated primarily by T lymphocytes.
Principal defence against intracellular microbes.
Has role in both innate and acquired immunity.
Classified based on receptor- ligands and effector
mechanisms.
Role are highly diverse , but limited to site of
action.
Multi level activation is required for cell function.
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Cell
mediated
immunity
vsHumoral
immunity
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Types of T lymphocytes in CMI
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Para-cortical region
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Dendritic cells and macrophages as
APC
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B cell as APC
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MHC Class I and II
Cytotoxic T cells ( CD8) Helper T cells ( CD4)
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MHC classes and T cells
APC
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Granules contain cytokines
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T cell receptor vs B cell receptor
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T cell receptor
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TCR complex
The TCR is part of a complex signalling machinery which
includes the TCR alpha beta dimer, the accessory
molecules CD4 or CD8 and a signal transduction modulemade up of various chains (CD3).
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TCR and co-stimulation signals
TCR CD4 CD3complex binding
is the first signal.
This is followed
by more thanone CO-
STIMULATORY
SIGNALS
Binding of CD28
on T cell with B7
on APC is the
second signal
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TCR ,co-stimulator and adhesion
molecules
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Role of costimulation in T cell activation
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T helper
cells hasvaried
roles
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T helper cells and their roles
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Th1 helper
cells are the
hostimmunity
effectors
against
intracellular
bacteria andprotozoa
Trigger for
production:
IL-12, IL-2
Effector
cytokine -
IFN-.
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Th2 helper cell
are the hostimmunity
effectors against
multi-cellular
helminths.
Triggered by IL-4
Effector cytokines: IL-4, IL-5, and IL-13
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Steps in activation of
T lymphocytes
Antigen recognition
Activation
Clonal selection
Clonal expansion
Clonal differentiation
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Targeted cell lysis by CD8 cells
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IL-2 is the major cytokine which stimulate the
proliferation and activity of B cells, T cells and NK
cells
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Role of IL 2 and IL2 receptors in T cell
proliferation
T cells are activatedand thet secrete IL-2.
They express IL-2
receptors on their
surface .The same cells
produce more IL-2
which then cause the
clone to proliferateas well as activate
other cells.
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Effector molecules for T cell subsets
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Migration
ofT effector
cells to site
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Antibody mediated immunity
Act on extracellular microbes
Mediated by B lymphocytes
Transform to plasma cells whichare the active multiplying forms (high nuclear- cytoplasmic ratio)
Secrete antibodies for action
Transfer to others by serum
Do not assist other cells
Block infection & eliminateextracellular microbes
Have active cells and memory cells
Involved in Type I , II and III
hypersensitivity
B cells can act as antigenpresenting cells
Cell mediated immunity
Act on phagocytosed microbes/intracellular microbes or viruses
replicating within the cell. Mediated by T lymphocytes
Require antigen to be presented viamajor histocompatibilty antigen foractivation
Secrete cytokines for action Transfer to others by lymphocytes
T helper cells assist B cells ( Tdependant)
Activate macrophages to killphagocytosed microbes ( T h cells)OR kill infected cells to eliminatereservoirs of infection
2 functional classes : T helper cellsand T cytotoxic cells
Have active cells and memory cells
Involved in Type IV hypersensitivity
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Control of T cell response
Co stimulatory signals and adhesion molecules
are required for functional activity of T cells.
Specialised T cells for extra cellular and
intracellular pathogens.
APCs pre-process the antigen and concentrate
the T cells in specialized lymphoid organs.
Concentration of T cytotoxic cells are far less
compared to T helper cells.
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THANK YOU
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