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Objectives 8
A.
Characteristics of Immune Responses
Every immune response has these characteristics:
1.
It is antigen specific
2.
It is systemic in scope
3.
It has memory
Red:
defects in
innate immunity
Green: defects in
specific
immunity
Yellow both systems
intact
Objective 9
Cell Mediated and Humoral Immunity
There are two interacting mechanisms in the immune response:
Cells Involved
Humoral Immunity
(Antibody Mediated)
B lymphocytes
and their
descendants
(plasma cells)
Mechanism
 plasma cells secrete
antibodies into body fluids
 antibody is transported in
body fluids to the site of
infection
 antibodies form complexes
with antigens and may
activate complement,
neutralize the antigen or
immobilize the antigen by
precipitation or agglutination
C. Definitions
Neutralization:
the antibody combines with the antigen and
blocks an active site, preventing antigen binding
to receptors on tissue cells
Agglutination:
antibodies are divalent (have more than one
binding site); they can bind to more than one
antigen at a time, forming cross linked clumps of
antigen/antibody complexes
Precipitation:
same as agglutination, but the antigen is a soluble
molecule; clumping causes the soluble antigen to
fall out of solution
Cell Mediated
Immunity
Cells Involved
Mechanism
T lymphocytes
T lymphocytes travel directly
to the site of infection and
act directly to lyse the
invader or indirectly by
secreting chemicals which
activate other immune
mechanisms
Objective 10
1.
Cells of the Adaptive IS
Antigen Presenting Cells:

include dendritic cells, macrophages. B lymphocytes
APCs engulf
antigens and present
fragments of the
engulfed antigens to
B cells and/or T cells
2.
B Lymphocytes and T Lymphocytes
a.
Maturation:
Subsets of B Lymphocytes and T Lymphocytes:
B Lymphocytes

Differentiate in bone marrow
where they acquire surface
antibody (B cell receptor)

They then travel to lymph
nodes and other lymphoid
tissues

Self reactive B cells are deleted in bone marrow or are
inactivated in peripheral lymphoid tissues (anergy)
Activation leads to mitosis and the production of plasma cells (which
secrete antibody) and memory cells
Plasma Cell:
antibody secreting cell that is a descendant of an activated
B lymphocyte
Memory Cell
descendant of a B lymphocyte that is programmed to
respond quickly to the same subsequent encounters with
the same antigen
T Lymphocyte:

lymphocyte that has differentiated in the thymus gland where it
acquires a T cell receptor (TCR)

It later travels to lymph nodes and other lymphoid tissues
T cells must acquire two properties while in the thymus
gland:
1. Must be able to bind to MHC class 1 antigens
found on the surfaces of nucleated body cells
(positive selection)
2. Must not react to self antigens bound to MHC
class 1 molecules on the surface of nucleated
body cells
T cells that fail to meet these criteria are removed from the
pool of developing T cells via apoptosis
T Cell Subsets:
Helper T Cells:
Specific Glycoprotein:
Activating Cell
CD 4
APC presentation of antigen

requires MHC class II antigen and
processed antigen
Generally, they activate
macrophages, attract
WBCs, assist in B cell
and T cell activation and
stimulate B cell and T cell
divsion
TH1 subset
TH2 subset
Is involved in
stimulating
inflammation,
activating
macrophages and
promoting cytotoxic
T cell activation
Is involved in
eosinophil
recruitment ;
stimulates B cell
division and
antibody
production
activation
Cytotoxic T Cells
Specific Glycoprotein: CD8
Activating Cell: APC presentation of antigen
Functions:
Directly attack and kill body cells
infected with virus or other
intracellular parasites, cancer cells
and transplanted tissue cells
Cytoxic T cells kill their targets by:
1. Inducing apoptosis
2. Releasing cytokines
Regulatory T Cells
Specific glycoprotein:
CD8
Regulate the immune response by releasing inhibitory
cytokines (IL 10, transforming growth factor ,
 interferon)
Gamma Delta T Cells
Activation: unknown
Function(s) Located mostly within epithelium
recognize markers expressed by
stressed or damaged cells
Objective 11
Antigens (Immunogens)
A. (Immunogens) antigens are substances which evoke
immune responses

typically, antigens are:
1.
Large, complex molecules
2.
Natural or man-made substances
3.
Are non-self
B.
A complete antigen has two properties:
Immunogenicity
can activate B cells and/or T cells
Reactivity
can react with activated T cells or antibodies
Immunogenicity
Reactivity

An incomplete antigen (hapten) is a molecule that is too small by
itself to be immunogenic; it can become immunogenic if it attaches to
a larger carrier protein and becomes part of a larger complex

Antigenic determinants (epitopes):
the portions of the antigen that are actually
immunogenic
Objective 12
The Humoral Response To Antigen
Objective 13
Immunity can be innate or acquired
through exposure to antigens:
Active Immunity
generated when an individuals B cells
encounter antigen and manufacture
antibodies as part of an immune response
(IR); long lasting protection is generated
Passive Immunity
generated when an individual receives
antibodies produced by another organism
(human or animal donor); shorter duration
because no memory is generated
Acquired Immunity
Naturally Acquired Immunity
immunity that is acquired as a result of a natural process (eg,
infection, placental transfer of antibody)
Artificially Acquired Immunity
immunity that is acquired when the antigen is introduced as
part of a clinical process (eg., vaccination)
Acquired Immunity specifically obtained through the
transfer of serum from one individual to another
individual is order to fight a disease is an example of:
Immunity that is passive and
artificial
Objective 14
Antibodies (Immunoglobulins)
Antibodies (immuoglobulins) are glycoproteins secrted by plasma cells.
They are located in interstitial fluid, plasma (gamma globulins) and in body
secretions
Antibody Structure

Four polypeptide chains
(two heavy, two light)

Chains are held
together by covalent
disulfide bonds (S=S)

each heavy and light chain has two functional areas:
Variable region
Constant region
consists of highly variable amino acid sequences and
forms the basis of antigen specificity; antigen
binds here
more conserved amino acid sequences, which
define the 5 antibody classes: IgA, IgD, IgE, IgG,
IgM
each class has its own effector functions
B. Antibody Classes:
Class
IgD
IgM
IgG
Generalized Location(s)
Structure
Attached to B cell
surfaces
Function(s)
B cell activation
First antibody released during a
primary infection; potent
agglutinator; activates compliment
Pentamer is found in
IF and plasma
Monomer is attached Monomer is involved in B cell
to B cell surfaces
activation
Plasma and IF
Effective against bacteria,
extracellular viruses and toxins;
activates complement and crosses
the placenta
IgA
Body Secretions
protects body surfaces and
prevents the attachment of
pathogens
IgE
Attached to mast
cell and basophil
surfaces
Triggers the release of histamine
and other mediators of inflammation
during allergic reactions
B cell receptors
are
IgM early in the
primary
response
and
IgD afterwards
Objective 15
The Cell Mediated Response
Objective 16
MHC
Major histocompatibility (MHC) antigens are self antigens that are
tolerated by the host, but not by other genetically different
individuals. There are two classes of MHC surface markers.
MHC Class I:
Location:
All cells except RBCs
Recognized by:
CD8 T cells
Function
activate cytotoxic T cells if body cells
are infected with intracellular parasites
such as viruses, if body cells become
malignant, or by non-self antigens
(eg, transplants)
MHC Class I antigens allow activated
cytotoxic T cells to interact with
the target cell
How MHC Class I and Endogenous Peptides are
displayed on all cells (except RBCs)
Note: TAP (transporter associated with antigen processing)
MHC Class II:
Location:
Dendritic cells, macrophages,
B cells
Recognized by:
CD 4 cells
Function
present antigens to helper
T cells
How MHC Class II and peptide derived from
extracellular antigen is displayed on an APC surface
The MHC Class I antigens of a donor will stimulate a recipient to reject a
transplanted tissue causing tissue incompatibility; it is the class I proteins
that are typed and matched prior to transfusion
autograft
: tissue is grafted from an individual back to himself
isograft
: tissue is transplanted between genetically identical
individuals
allograft
xenograft
: tissue is transplanted between two members of the same
species (not genetically identical)
: tissue is transplanted from a member of one species to
a member of another species
A young female soccer player tears her ACL during
practice and decides to have it replaced with a graft.
She is given several surgical options – decide which
category each graft below falls in to:
a. A porcine) pig derived ligament (Z-lig)
xenograft
b. A section of the patient’s own patellar tendon:
autoograft
c. A section of hamstring from a cadaver (not a
relative):
allograft