4-Cell Mediated Immunity

7/23/2019 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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4-Cell Mediated Immunity