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The immune system and
the oral cavity
2nd part
Adaptive or acquired immunity
Done by Dr. Zubaida Najat
Adaptive Immune System –
Introduction
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Adaptive: responds to specific foreign substances
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Innate & adaptive mechanisms work together
Types of Acquired Immunity
Figure 21.11
Types of Acquired Immunity
1- Passive acquired immunity
includes
a- Naturally passive acquired immunity
antibodies are pass through placenta of fetus
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b- Artificially passive acquired immunity:The
injection of alredy prepared antibodies such as
gamma globulin
2- Active
immunity
a- Natural active acquired immunity
Following clinical or subclinical infections
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b-Artificial active acquired immunity:-
Following vaccination with live or killed
infectious agents or their products
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Adaptive Immune System: Cells
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Lymphocytes
 T-cells
 B-cells
Antigen Presenting Cells (APCs)
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Acquired immunity is triggered in vertebrates when a
pathogen evades the innate immune system and
(1) generates a threshold level of antigen and
(2) generates "stranger" or "danger" signals activating
dendritic cells
The major functions of the acquired immune system
include:
Recognition of specific "non-self" antigens in the presence of
"self", during the process of antigen presentation.
Generation of responses that are tailored to maximally
eliminate specific pathogens or pathogen-infected cells
systemic action .
Development of immunological memory, in which pathogens
are "remembered" through memory B cells and memory T
cells.
Antibody Targets & Functions
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Immune complex formation = antigen-antibody binding.
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All the following events are initiated by antigen-antibody
binding.
Complement fixation:
Neutralization:
Agglutination:
Precipitation:
Inflammation & phagocytosis prompted by debris
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Adaptive, Humoral Immunity
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Antigen – “any substance when introduced
into the body stimulates the production of an
antibody”
– Bacteria, fungus, parasite
– Viral particles
– Other foreign material
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Pathogen – an Antigen which causes
disease
Adaptive, Humoral Immunity
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Complete antigens (proteins, nucleic acids,
lipids, polysaccharides):
 Immunogenicity:
the ability to stimulate specific
lymphocytes & specific antibodies
 Reactivity: the ability to react with activated
lymphocytes & antibodies
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Hapten (an incomplete antigen): a smaller
molecule that is not immunogenic until attached
to proteins
Adaptive, Humoral Immunity
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Antigenic determinants: sites on an antigenic molecule
that are immunogenic
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Epitope
Major Histocompatibility Complex (MHC): cell surface
glycoproteins associated with self recognition
Humoral Immunity

Active humoral immunity:
 B-cells
encounter & respond to antigen to produce an
antibody
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Passive humoral immunity:
 Introduced
“non-native” antibody
Antibodies
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Antibody – “a Y-shaped protein,
found on the surface of B-Cells
or free in the blood, that
neutralize antigen by binding
specifically to it”
Also known as an
Immunoglobulin
Constant (C) region defines
antibody class
determines chemical & cellular
interactions
determines how class functions
to eliminate antigens
Humoral Mediated
Immunity
Antibodies
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Immunoglobulins & gamma globulins
Structure
 variable
 hypervariable
 constant
Figure 21.13a
Antibody Classes
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Antibody Classes: IgM, IgG, IgA, IgD, IgE
(Ig = immunoglobulin)
Antibody Classes
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IgM: occurs as a monomer & a pentamer
 Occurs
 The
on the B-cell surface (Monomer).
Ig of early primary plasma cell response,
circulating antibody; a potent agglutinator.
Complement binding (Pentamer).
Antibody Classes
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IgE: the Ig associated with allergies.
 Stem binds to mast cells & basophils.
 Receptor binding results in histamine release
& inflammation.
 Found mostly in mucosa of respiratory & GI
tract (Monomer).
Antibody Classes
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IgG: the most abundant circulating Ig. The
dominant circulating Ig of the primary & the
secondary response. Crosses the placenta.
Complement binding (Monomer).
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IgA: the Ig of secretions. Helps prevent antigen
penetration of membranes (Dimer).
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IgD: the Ig of B-cell activation. Found on B-cell
surface (Monomer).
Adaptive Immune System: Cells
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Immunocompetence: as T- or B-cells mature
they become immunocompetent, they display
receptors on their cell membrane for a specific
antigen.
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All of the receptors on one cell are identical;
immunity depends upon genetic coding for
appropriate receptors.
Immunocompetent B or T cells
Key:
Red
bone marrow
= Site of development of immunocompetence
as B or T cells; primary lymphoid organs
= Site of antigen challenge & final
differentiation to activated B & T cells
Immature
lymphocytes
Circulation in
blood
= Site of lymphocyte origin
1
1 Lymphocytes destined to become T
1
Thymus
Bone
marrow
cells migrate to the thymus & develop
immunocompetence there. B cells
develop immunocompetence in red
bone marrow.
2
Immunocompetent,
but still naive,
lymphocyte
migrates via blood
2
2 After leaving the thymus or bone
marrow as naive immunocompetent
cells, lymphocytes “seed” the lymph
nodes, spleen, & other lymphoid
tissues where the antigen challenge
occurs.
Lymph nodes,
spleen, & other
lymphoid tissues
3 Mature (antigen-activated)
3
Activated
immunocompetent
B & T cells
recirculate in blood
& lymph
3
immunocompetent lymphocytes
circulate continuously in the
bloodstream & lymph & throughout
the lymphoid organs of the body.
Figure 21.8
Adaptive Immune System: Cells
Antigen Presenting Cells (APCs)
APCs ingest foreign material, then present antigenic
fragments on their cell surface where they are
recognized by T-cells
APCs: Macrophages & B lymphocytes
Interactions between APCs & lymphocytes &
lymphocyte-lymphocyte interactions are critical to
immune response
Adaptive, Humoral response
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Humoral response (clonal selection)
Figure 21.14
Cellular Immunity
Tcell
CD4& CD8
Adaptive Immune
System: Cells
Lymphocytes: initially uncommitted
T-cells: are sorted in the Thymus
Positive selection: recognize
MHC survive
Negative selection: react
against to self-antigens on
MHC killed
2% of initial T-cell precursors
T-cells manage the immune
response
Cell Mediated Immune Response
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T-cell activation: involves recognition of PM
surface antigens only
 Antigen
is combined with MHC & displayed on PM
 T-cell receptors: bind to the MHC & are stimulated by
the associated antigen
 The addition of a co-stimulator (cytokines,
interleukins, etc) prompts the T-cell to form a clone
Helper T Cells (TH)
Figure 21.17a
Professional APCs
+
CD4 Th1-Cells
Cell Mediated: MHC
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MHC occurs as two classes
 MHC
I on virtually all tissue cells
 MHC II only on PM some immune system cells
Cell Mediated: MHC display properties
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MHC I on virtually all tissue cells
 Display only proteins produced inside the cell
 Endogenous antigens = foreign proteins produced by the
cell (viral / cancer)
 Stimulate the CD8* cell population
 form cytotoxic T-cells (Killer T, TC)
 *formerly T8 cells
Cell Mediated: MHC display properties
Figure 21.16b
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MHC II found only on PM of B-cells, some T-cells & APCs
 Display proteins derived from a phagocytized target
 Exogenous antigen: foreign protein from outside the cell –
presented to PM surface
 Stimulates the CD4* cell population
 form Helper T-cells (TH)
Cell Mediated: T-cell roles
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Helper T-cells (TH) stimulate B-cells
& other T-cells to proliferate
Figure 21.18
Cell Mediated: T-cell
roles
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Activated TH cells interact with Bcells displaying antigen & produce
cytokines that prompt the B-cell to
mature & form antibody
Cell Mediated:
T-cell roles
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TH cells also produce cytokines
that promote TC cells
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TH cells recruit other WBCs &
amplify innate defenses
(inflammatory)
Subpopulations of TH cells
specialize in specific sets of
activations
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Cell Mediated: T-cell roles
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Cytotoxic T-cells (TC, Killer T): directly attack &
kill cells with specific antigen
Activated TC cells are co-stimulated by TH cells
Cell
Mediated:
T-cell roles
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TC mechanism (Cytotoxic T-cells, Killer T)
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TC binds to cell & releases perforin & granzymes
In the presence of Ca2+ perforin forms pores in target cell PM
Granzymes enter through pores & degrade cellular contents
TC then detaches & moves on
Macrophages clean up
Cell Mediated: T-cell roles
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Other T-cells
 *Regulatory
T-cells (TReg): release inhibitory cytokines
that suppress B-cell & T-cell activity
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Help to prevent autoimmune events
*formerly Suppressor T (TS)
 Gamma
Delta T-cells (Tgd): live in the intestine.
Function in surveillance & are triggered much like NK
cells
Cellular Mediated Immunity
Summary of the Primary Immune Response
Figure 21.19