b cell immunity
DESCRIPTION
TRANSCRIPT
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IMMUNITY
• The capability to resist any organism or toxin that tend to damage the tissues and organs.
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Immunity
Innate = ability to resist damaging organisms and toxinsskin, gastric acids, tissue neutrophils and macrophages, complement, NK cells
Acquired = specifichumoral ----> circulating antibodies(B-cell) cellular ----> activated cells(T-cell mediated)
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Preprocessing of the T and B lymphocytes
• Thymus gland preprocesses the T lymphocytes
• Liver and bone marrow preprocess the B lymphocytes
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Lymphoid tissue
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• Millions of specific types of lymphocytes are stored in the lymphoid tissue.
• All the different lymphocytes that are capable of forming one specificity of antibody or T cell are called a ‘clone of lymphocyte’.
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Sequence
Dormant lymphocytes
Invasion of body by foreign antigen
Phagocytosis by macrophages
Presentation of antigen to lymphocytes
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Antigen
An antigen is a substance that can induce
an immune response when introduced into
an immunocompetent host and that can react
with the antibody produced from that response.
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Bone Marrow
Pre-BCell
Pre-TCell T-Cell
T8-supressor
T4-helper
B-Cell Plasma Cell
IgG IgA IgM IgD IgE
Interactions between T- and B-Cells
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Humoral immunity and Antibodies
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Formation of antibodies by plasma cells
• Dormant B lymphocyte• Exposure to a specific antigen• Macrophage plays role in the activation
process• Helper T cells also contribute in this activation
process
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• These B lymphocytes enlarge to form lymphoblast.
• Further diferentiate into plasmablast• The mature plasma cells(antibody factories)
then produce gamma globulin antibodies.
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Formation of Memory cells-difference between primary and
secondary response
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virgin cellsfirst exposure to antigen
second exposure to antigen
activated cellsmemory cells
Formation of Activated and Memory Cells
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self-antigens
death
Central lymphoid organ Peripheral lymphoid organ
stimulation
self-antigens
death
inactivation
Loss of Antigens to Self
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Antibodies
antigenbindingsite
hinge region
light chain
heavy chainFab fragment
Fc fragment
IgA, IgD, IgE, IgG, IgM
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IgM Antibody
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Antibodies• IgG
- 80% total, cross placenta, opsonization
• IgM- first produced, 10-15% total, activate complement
• IgD- not known, may help CD4 Th
• IgA- body fluid, tears, bronchiole secretions, saliva
• IgE- allergic reactions, histamine release
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Mechanism of action of antibodies
Direct Action Complement System
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Direct action of antibodies on invading agents
1. AGGLUTINATION2. PRECIPITATION3. NEUTRALIZATION4. LYSIS
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Complement System
Series of ~ 20 proteinsActivated by microorganismsWill coat the microorganismsPresent normally among plasma proteins
The enzyme precursors can be activated by the
so called ‘classical pathway’
s
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complement
bacteria phagocyte bacteria
2. chemotaxis1. lysis 3. opsonization
Functions of Complement Activation
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Antibody-Activated Phagocytosis
Fc receptorbacterium
opsonization
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IgE and Histamine Release
IgE receptor
histaminevesicles
binding of IgEto Fc receptor
antigenantigen
release of histamine
binding of antigen
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Thank You
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T-cells
Act over a short range
Interact with another cell in bodyCan kill or signal other cell
Only recognize antigen when presentedon surface of target cell
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T-cells
Cytotoxic Cellskill infected cells
Helper Cells (two types)activate macrophages and B-cells
Suppressor Cellsregulate activity
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TH1 TH2
TC LGL
B
Antibody Production
Virally infected cell andsome tumor cells
Antigenpresentation
Antigenpresentation
activation activation cytotoxicity
macrophage
T-Cell Function
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Mhc-molecules
MHC-I present foreign peptides to cytotoxic cells
MHC-IIpresent foreign peptides to helper cells
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CYTOTOXIC T-CELLS HELPER T-CELLS
Tc Th
Class IMHC
Class IIMHC
foreignprotein
infectedtargetcell
antigen-presentingcell
Mhc-molecules
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Helper T-cells
Helper T-Cells recognize foreign antigen bound toMHC-II proteins on surface of antigen-presenting cells
Helper T-Cells stimulate macrophages and B-cells
Two signals are required for activation of Helper T-Cells
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Activation of Helper T-cells
Th
antigen-presentingcell
signal 1
signal 2
activation
signal 2 is chemical (interleukin-1) or membrane bound molecule
CD4
antigen
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Activation of Helper T-cells
Th
antigen-presentingcell
signal 1
signal 2
Th
Il-2 receptor
Il-2
Th Th
proliferation
CD4
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Cytotoxic T-cells
Cytotoxic T-Cells recognize viral protein fragments onsurface of infected cells.
Cytotoxic T-Cells induce infected cells to kill themselvesBind to infected cellsInduce cell deathPunch holes in cell membrane
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Cytotoxic T-cells
Class IMHC
Tc
infectedtargetcell
CD8
Perforin discharge
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Natural Killer
• destroy virus-infected cells• do not express antigen specific receptors• cells with low levels of MHC I• induce cells to undergo apoptosis
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TC
TCRCD8
MHCClass I
Inhibitoryreceptor
NK
Target
No MHCClass I
NK receptor