The Immune Response I. Specific immunity

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The Immune Response

I. 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


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

II. 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

Nucleic Acids
Some lipids


C. Antigenic Determinants


Specific part of the antigen molecule that the antibody is directed against

Projections from the surface of the antigen

D. Common Antigenic Determinants


Amino acid R groups

Organic Acids


E. Humoral Immune system

Produces antibodies as a result of stimulation by antigens

F. Antibodies

Specific proteins that react with antigens

Present in



Other bodily fluids

Proteins produced by the host

Interfere with the normal functioning of the antigen

Allow the host to destroy antigen

G. 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

H. 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

I. 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

Lymph nodes

J. Latent period

Occurs immediately after first exposure

Lasts several days

No antibody can be detected in blood

  1. Primary response

Initial production of a low level of antibody

Antigen localized in cells of lympathic system soon after it enters the body



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


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

M. Ability to form antibodies

Vertebrates can produce between 10 and 100 million different kinds of specific antibodies

Dependent on


Nutrient state

Hormonal balance

Depressed by

steroid hormones

Exposure to radiation

Certain viruses

N. Development of T cells

Some released into blood

70-80% of circulating lymphocytes are T cells

Other T cells do not circulate

Found in

Lymph nodes


Cells predetermined to become T cells

Leave the bone marrow

Migrate to the thymus gland

Complete their develop into T cells

O. Lymphocytes

Cells primarily responsible for the immune response

Derived from stem cells in bone marrow

Small mononuclear (single nucleus) leucocytes

Immunologically competent (or precursors of such cells)
109 produced each day

Migrate through the circulatory or lymphatic systems to lymphoid tissue

Produce lymphocyte colonies

P. Types of lymphocytes

B lymphocytes or B cells

T lymphocytes or T cells

Q. 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

R. Antibody production

Requires interaction of three types of white blood cells


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. 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

III. 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


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

Have large number of hydrolytic granules

Kill bacteria that cause intracellular infections

IV. 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


Attenuated strains

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