The Immune Response
I.
II.
Specific immunity
A.
Occurs only in vertebrates
Involves highly specific defense response
B.
Occurs
When the host is exposed to
Microorganism or its products
Some tumor cells
Certain macromolecules (Substances in the environment)
C.
Immune response
Specific series of defensive actions that occurs throughout the
body
Lymphocytes recognize presence of foreign substances and act to
eliminate them
D.
Three Characteristics of the immune system
1. Tolerance
Distinguishes self from non-self
Does not attack host macromolecules
Attacks foreign macromolecules
2. Specificity
Attacks foreign macromolecules with immune system cells
that are specific for the particular foreign macromolecules
3.Memory
Once immune system has recognized and reacted with a
specific macromolecule it is able to react very quickly to
subsequent exposure to the same macromolecule
E.
Immune system composed of two interdependent parts
1. Antibody mediated immunity - Humoral
2. Cell mediated immunity
* Neither part functions without the other
Humoral Immunity
A.
Antibody mediated immunity
Neutralize foreign macromolecules by action of specific antibodies
B.
Antigen
Any foreign macromolecules that induces the immune response
Invading microorganisms contain a variety of antigens
Common Antigens
Proteins
Nucleic Acids
Polysaccharides
Some lipids
Lipopolysaccharides
C.
D.
E.
F.
G.
H.
I.
Antigenic Determinants
Epitopes
Specific part of the antigen molecule that the antibody is
directed against
Projections from the surface of the antigen
Common Antigenic Determinants
Sugars
Amino acid R groups
Organic Acids
Hydrocarbons
Humoral Immune system
Produces antibodies as a result of stimulation by antigens
Antibodies
Specific proteins that react with antigens
Present in
Blood
Serum
Other bodily fluids
Proteins produced by the host
Interfere with the normal functioning of the antigen
Allow the host to destroy antigen
Antibody structure
Five classes of antibodies found in mammals
All very similar
Consist of four polypeptide chains
Two identical light chains
Two identical heavy chains
Linked by disulfide bonds
Antibody Molecule
Antigen binding sites
Chains folded to form two identical antigen binding sites
on the surface of the antibody
Interact with antigens in a lock and key fashion
Antibody-Antigen combination
Development of humoral immunity
Specific sequence of events occurs when the host is exposed to an
antigen
Antigen localized in the cells of the reticuloendothelial system
soon after it enters the body
Liver
Spleen
Lymph nodes
J.
Latent period
Occurs immediately after first exposure
Lasts several days
No antibody can be detected in blood
K.
Primary response
Initial production of a low level of antibody
Antigen localized in cells of lympathic system soon after it enters
the body
Spleen
Liver
L.
Antibody development
Log phase
Antibody level
Rises logarithmically
Plateau phase
Antibody titer stabilizes
No increase or decrease in the number of antibodies
Decline phase
Antibodies
Combine with the antigen
Removed from the circulation by phagocytes
Booster response
Booster response - Secondary response
Rapid sudden increase in antibody level following a second
or subsequent exposure to the same specific antigen
Body mounts heightened response to same specific antigen
Antibody level may be 10-1000 times greater than during
the primary response
Ability to form antibodies
Vertebrates can produce between 10 and 100 million different
kinds of specific antibodies
Dependent on
Age
Nutrient state
Hormonal balance
Depressed by
steroid hormones
Exposure to radiation
Certain viruses
Development of T cells
Some released into blood
70-80% of circulating lymphocytes are T cells
Other T cells do not circulate
M.
N.
O.
P.
Q.
R.
Found in
Lymph nodes
Spleen
Cells predetermined to become T cells
Leave the bone marrow
Migrate to the thymus gland
Complete their develop into T cells
Lymphocytes
Cells primarily responsible for the immune response
Derived from stem cells in bone marrow
Small mononuclear (single nucleus) leucocytes
Non-phagocytic
Immunologically competent (or precursors of such
cells)
109 produced each day
Migrate through the circulatory or lymphatic systems to
lymphoid tissue
Produce lymphocyte colonies
Types of lymphocytes
B lymphocytes or B cells
T lymphocytes or T cells
B cell development
Complete differentiation in
Fetal liver
Adult bone marrow
B cell differentiation
Distributed by the blood
Make up 20-30% of the circulating lymphocytes
Antibody production
Requires interaction of three types of white blood cells
Macrophage
B lymphocyte
T helper cell
Macrophage, T cell, and B cell complex
Macrophage (phagocyte)
Ingests invading microorganisms
B lymphocytes (B cells)
Have specific antigenic receptors on their surface
T helper cell
Also have specific receptors on their surfaces which bind to
specific antigen parts on the surface of the macrophage
Produces chemical that stimulates the B cells to divide
repeatedly
Dividing B cells produce
Many plasma cells
Memory B cells
S.
III.
Complement system
Combination of antigen and antibody has minimal effect until the
complement system is activated
Group on proteins in blood serum
Effective against Gram negative bacteria
Activated by the antibody-antigen comples
Each protein has specific antibacterial function
T.
Complement fixation
Complement proteins irreversibly changed during reaction with
antigen-antibody complex
Can’t be reused
Basis of many medical diagnostic tests
Cellular immune response
A.
General
Involves T cells
Does not involve
B cells or antibodies
B.
T cells
Become Immunologically competent
As result of contact with specific antigens
Competent T cells
Release lymphokines
Attack antigens directly
Attract phagocytes
Cause the inflammatory response
C.
Cellular Immune response
Takes about 24 hours to develop after contact with the antigen
D.
T.B. skin test
Relies on the cellular immune response
Detects past or current infections with Mycobacterium tuberculosis
Mycobacterium antigens injected subcutaneously into the forearm
T.B. skin test-results
No infection or no immunity  no reaction
Immunity or active infection  positive reaction
T.B. skin test-positive reaction
Hard raised welt in the area of injection
T cells activated by past encounters with Mycobacterium
respond by producing lymphokines
Lymphokins
Attack Mycobacterium antigens directly
Attract phagocytes to the area of the injection
Cause the inflammatory response
E.
Killer Macrophages
Activated T cells produce lymphokines
Act on developing macrophages killer macrophages
Better able to kill invading foreign organisms
IV.
Have large number of hydrolytic granules
Kill bacteria that cause intracellular infections
Immunology and disease prevention
A.
Passive Immunity
Organism is protected against by antibodies produced by another
organism
Short term immunity
Antibodies prevent or cure disease for a short time
Gradually lost
Organism cannot produce more antibodies for itself
Can be reinfected by the same pathogen
B.
Natural passive immunity
Maternal antibodies transferred to fetus before birth
Maternal antibodies protect the neonate
Antibodies secreted into milk also protect baby
C.
Active immunity
Occurs when organism is stimulated to develop its own antibodies
Develops in response to infection or injection of specific antigen
Individual is fundamentally changed
Able to produce specific antibodies throughout life
D.
Vaccine
Used to induce antibody formation
Harmless product containing antigens from pathogens
Organism itself
Killed bacteria
Viruses
Attenuated strains