cell mediated acquired immunity
TRANSCRIPT
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Cell-Mediated immuneresponse
Recognition and the binding of a maturelymphocyte to an antigen induces thelymphocyte to divide rapidly.
This proliferation of lymphocytes is calledclonal selection. Two types of clones areproduced: short-lived activated effector cellsand long-lived memory cells
These effector cells activate B cells orMacrophages, or destroys infected, tumor, ortransplanted cells directly or through release of
soluble mediators i.e. cytokines and Controls
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Why it is known as cellmediated
It is based on type of microbial invaders those are facedby immune system.
Microbial invaders fall into two broad categories-In one category-organisms that originate outside the
body including most bacteria, fungi as well as manyprotoza and invading helminths.The second category consists of the organisms that
originate or live inside the bodys own cells includingviruses and intracellular bacteria or protozoa.
Cell mediated immune system is directed againstintracellular or endogenous invaders that invade cells.
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How the antigen ispresented to lymphocytes
All nucleated cells of body trap endogenos antigenswith the help of MHC 1 receptors on their surface and
then present to cytotoxic T- lymphocytes also having
receptors for trapping.
Its the main way of cell mediated immunity.
Professional antigen presenting cells also help in
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Types of antigenpresenting cells (APC)
1. Dendritic cellsPhagocytic dendritic cells (DC) of tissues
(Most potent stimulators of T cell responses)
Germinal Center Dendritic Cells (GCDCs)Thymic Interdigitating Dendritic Cells (IDCs)
Interstitial Dendritic Cells
2. B cells as APCPresent Ag to T cells (TH2)
3. Macrophages
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The Role of the MHCIn infected cells, MHC molecules bind and transport
antigen fragments to the cell surface, a process
called antigen presentation.
T cell can then detect the antigen fragmentdisplayed on the cells surface.
Depending on their source, peptide antigens are
handled by different classes of MHC molecules,
mainly 2 are involved in the cell mediated immunity
which are as follows-
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The Two Classes Of MHCMolecules
MHC Class I
Class I MHC molecules are found on almost all
nucleated cells of the body and Presents Agderived from intracellular source/cytosol.
They display peptide antigens to cytotoxic T
cells
cytotoxic T cells kill target
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MHC Class II
Class II MHC molecules are located mainly on
dendritic cells, macrophages, and B cells and
Present Ag derived from extracellular or cell-bound
source.
These antigen-presenting cells then displayantigens to inflammatory T cells and helper T cells.
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T Cells
Originate in stem cells in bone marrow
Change to T cells in thymus
Become sensitized to specific antigenProduce cell-mediated immunity following T cell
activation (in peripheral lymphoid organ) -
Cytotoxic T cells (Tcyt) Kill infected targetcells Inflammatory (TH1) and Helper (TH2) T
cells Activation of other cells (macrophages
and B cells, respectively)
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Way of functioning of T-cells
Inflammatory T cells = TH1
Activate macrophages
MHC class II-restricted
Helper T cells (TH2)
Help to eradicate extracellular pathogens
Activated helper T cells secrete cytokines that
stimulate other lymphocytes and Provide
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Cytotoxic T cells = Tcytv Recognize virus-infected cellsv Kill infected cells directly by inducing
apoptosis (programmed cell death cellsuicide)
v MHC class I-restricted
Natural Killer Cells
Recognize virus-infected cells and cancer cells
They directly release lethal chemicals, leading to
apoptosis
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Helper T cellsParticipate in both the Humoral and Cell-Mediated Immune Responses
The HIV virus attacks Helper T cells
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T- cell receptorEach T cell receptor consists of two different
polypeptide chains.
The tips of the chain form a variable (V) region; the
rest is a constant (C) region.
T cells can bind to an antigen that is free or on the
surface of a pathogen
A single T cell has about 100,000 identical antigen
receptors.
Fig 43 9
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Fig. 43-9
Anti gen-
binding
site
Antigen-
bindingsite
Antigen-
binding
site
Disulf ide
bridge
Variabl
eregions
Constant
regions
Transmembrane
region
Plasma
membra
ne
Light
chain
Heavychains T c
ell
ch
ain
ch
ain
DisulfidebridgeCytoplasm of T cell
(b) T cellreceptor
Cytoplasm of B cell(a) B cell
receptor
B cell
V V
C C
V V
C C C C
VV
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Steps of the Cell MediatedResponse
1. Infected cell presents antigen on ClassI MHC
2. Cytotoxic T Cell recognizes antigenand binds to it
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Steps of the Cell MediatedResponse
3 . Cytotoxic T Cell reproduces (clonesitself)
4. Cytotoxic T Cells bind to antigen boundto infected cells and release perforin
to lyse infected cells
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Response to InfectedCells
Cytotoxic T cells are the effector cells in cell-mediatedimmune response.
Cytotoxic T cells make CD8 , a surface protein that
greatly enhances interaction between a target cell and
a cytotoxic T cell.
Binding to a class I MHC complex on an infected cell
activates a cytotoxic T cell and makes it an active killer.
The activated cytotoxic T cell secretes proteins that
destroy the infected target cell.
Fig 43-17
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Fig. 43 17
Antigen-
presenting
cell
Peptideantigen
Cell-mediated
immunity(attack
oninfected
cells)
Class II MHC
moleculeC D4
TCR (T cellreceptor)Helper T
cellHumoral
immunity(secretio
n of antibodies by
plasmacells
)
Cytotoxic Tcell
Cytokines
Bcell
Bacterium
+
+ +
+
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Memory T-cells
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Overall diagramatic presentation of cell mediated immunity
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Primary versus SecondaryResponse
Primary Response = initial immune
response to antigen -
The first exposure to a specific antigen represents theprimary immune response
During this time, effector B cells called plasma cells
are generated, and T cells are activated to theireffector forms
Secondary Response = immune response when-
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Primary vs. SecondaryResponse
The secondary response is much faster than theprimary response
More antibody & T cell production in a shorteramount of time
Primary
response
Secondary Response
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