Specific and Non Specific
Immune Responses and
Prepared by :
TARIQ JAVED GILL.
B. Sc. N Semester I Year 2012-2014
At the end of session the audience will be
Define specific and non specific immune responses.
Understand how the Immune System works.
Explain about the common Immune Disorders.
• The immune response is how your body recognizes and defends itself against
bacteria, viruses, and substances that appear foreign and harmful.
• The immune system protects the body from possibly harmful substances by
recognizing and responding to antigens. Antigens are substances (usually proteins)
on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such
as toxins, chemicals, drugs, and foreign particles (such as a splinter) can also be
antigens. The immune system recognizes and destroys substances that contain
• Your own body's cells have proteins that are antigens. These include a group of
antigens called HLA antigens. Your immune system learns to see these antigens as
normal and usually does not react against them.
• We survive because our body’s immune system defends us against pathogens
(disease-causing agents). The immune system consists of cells and tissues found
throughout the body. The body uses both nonspecific and specific defense
mechanisms to prevent infection and to detect and destroy pathogens.
Non Specific Immune Response
INNATE IMMUNITY OR NON SPECIFIC IMMUNITY
Innate, or nonspecific, immunity is the defense system with
which you were born. It protects you against all antigens.
Innate immunity involves barriers that keep harmful materials
from entering your body. These barriers form the first line of
defense in the immune response. Examples of innate immunity
Enzymes in tears and skin oils
Mucus, which traps bacteria and small particles
Stomach acid 5
First line of nonspecific defenses
The body’s surface defenses are nonspecific, meaning they do not target
SKIN is the first of our immune system’s nonspecific defenses against
• Skin acts as a nearly impenetrable barrier to invading
pathogens, keeping them outside the body.
• This barrier is reinforced with chemical weapons – oil and sweat!
• Oil and sweat make the skin’s surface acidic, inhibiting the growth of
many pathogens and sweat contains
• the enzyme lysozyme which digests bacterial cell walls.
• Internal surfaces of the body through which pathogens can pass are
covered by MUCOUS MEMBRANES.
• Mucous membranes are layers of epithelial tissue that produce
sticky, viscous fluid called mucus.
• Mucous membranes line the digestive system, nasal
passages, lungs, respiratory passages, and the reproductive tract.
• Skin and mucous membranes work to prevent any pathogens from
entering the body; nevertheless, sometimes these defenses are
• When invaders reach deeper tissue, a second line of nonspecific
defenses takes over.
Second line of nonspecific defenses
When the body is invaded, four important non-specific
defenses take action:
1. The Inflammatory Response
Caused by injury or local infection, like a cut or a scrape
Is a series of events that suppress infection and speed recovery
Imagine that a splinter has punctured your finger, creating an
entrance for pathogens.
Infected or injured cells in your finger release chemicals, including
Histamine causes local blood vessels to dilate, increasing blood
flow to the area.
Increased blood flow brings white blood cells to the infection
site, where they can attack pathogens.
This also causes swelling and redness in the infected area.
The whitish liquid, or pus, associated with some infections contains
white blood cells, dead cells and dead pathogens.
Inflammation aids the fight against infection by increasing
blood flow to the site and raising temperature to retard
The events in a local inflammation. When an invading microbe has
penetrated the skin, chemicals, such as histamine and
prostaglandins, cause nearby blood vessels to dilate. Increased blood
flow brings a wave of phagocytic cells, which attack and engulf invading
2. The Temperature Response
When the body begins its fight against pathogens, body temperature
increases several degrees above the normal value of about 37°C (98.6°F).
This higher temperature is called a fever, and it is a common symptom of
illness that shows the body is responding to an infection.
Fever is helpful because many pathogenic bacteria do not grow well at
But, very high fever is dangerous because extreme heat can destroy
important cellular enzymes.
Temperatures greater than 39°C (102°F) are considered dangerous and
those greater than 41°C(105°C) can be fatal.
3. Proteins that kill or inhibit pathogens
Certain proteins circulate in the blood and become active when
they encounter certain pathogens.
Then they form a membrane attack complex (a ring-shaped
structure that ruptures the cell membrane of pathogens).
Another nonspecific defense is interferon (a protein released by
cells infected with viruses).
Causes nearby cells to produce an enzyme that prevents viruses
from making proteins and RNA.
4. White Blood Cells
The most important counterattacks in the second line of
nonspecific defenses are carried out by three types of white
blood cells: Neutrophils, Macrophages and Natural killer cells.
These cells patrol the bloodstream, wait within the tissues for
pathogens, and then attack the pathogens.
Each kind of cell uses a different mechanism to kill pathogens:
Is a WBC that engulfs and
Most abundant type of WBC
Sacrifice themselves to
defend the body
Engulf bacteria and then
release chemicals that kill
the bacteria and themselves
Ingest and kill pathogens they encounter
Clear dead cells and other debris from the body
Most travel through the body in blood, lymph, and fluid between cells
Concentrated in particular organs, especially the spleen and lungs.
Natural Killer Cells
Large WBC that attacks cells infected with pathogens
Destroy an infected cell by puncturing its cell membrane
Water then rushes into the infected cell, causing the cell to swell
One of the body’s best defenses against cancer – can detect cancer
cells before a tumor can develop
SPECIFIC IMMUNE RESPONSE
The Immune Response:
The Third Line of Defense
What happens when pathogens occasionally
overwhelm your body’s nonspecific defenses?
Pathogens that have survived the first and
second lines of nonspecific defenses still face a
third line of specific defenses the immune
SPECIFIC IMMUNE RESPONSE
Few of us pass through childhood without contracting some sort of
infection. Chicken pox, for example, is an illness that many of us
experience before we reach our teens. It is a disease of
childhood, because most of us contract it as children and never catch it
again. Once you have had the disease, you are usually immune to it.
Specific immune defense mechanisms provide this immunity.
DISCOVERY OF SPECIFIC IMMUNE SYSTEM
In 1796, an English country doctor named Edward Jenner carried out an experiment
that marks the beginning of the study of immunology. Smallpox was a common and
deadly disease in those days. Jenner observed, however, that milkmaids who had
caught a much milder form of “the pox” called cowpox (presumably from cows)
rarely caught smallpox. Jenner set out to test the idea that cowpox conferred
protection against smallpox. He infected people with cowpox and as he had
predicted, many of them became immune to smallpox. We now know that smallpox
and cowpox are caused by two different viruses with similar surfaces. Jenner’s
patients who were injected with the cowpox virus mounted a defense that was also
effective against a later infection of the smallpox virus. Jenner’s procedure of
injecting a harmless microbe in order to confer resistance to a dangerous one is
called vaccination. Modern attempts to develop resistance to
malaria, herpes, and other diseases often involve delivering antigens via a harmless
vaccinia virus related to cowpox virus.
Key Concepts of Specific
Antigens are molecules, usually foreign, that provoke a specific
immune attack. This immune attack may involve secreted proteins
called antibodies, or it may invoke a cell-mediated attack.
A large antigen may have several parts, and each stimulate a different
specific immune response. In this case, the different parts are known
as antigenic determinant sites, and each serves as a different
antigen. Particular lymphocytes have receptor proteins on their
surfaces that recognize an antigen and direct a specific immune
response against either the antigen or the cell that carries the antigen.
Lymphocytes called B cells respond to antigens by producing
proteins called antibodies. Antibody proteins are secreted into
the blood and other body fluids and thus provide humoral
immunity. (The term humor here is used in its ancient
sense, referring to a body fluid.)
Other lymphocytes called T cells do not secrete antibodies but
instead directly attack the cells that carry the specific antigens.
These cells are thus described as producing cell-mediated
Third line of defense – Specific immune response
The immune response
consists of an army of
individual cells that rush
throughout the body to
combat specific invading
Cells Involved in the Immune Response
WBC are produced in bone marrow and circulate in blood and lymph. Of
the 100 trillion cells in your body, about 2 trillion are WBC.
Four main kinds of WBC participate in the immune response:
macrophages, cytotoxic T cells, B cells, and helper T cells.
Each kind of cell has a different function:
Macrophages – consume pathogens and infected cells
Cytotoxic T cells – attack and kill infected cells
B cells – activate both cytotoxic T cells and B cells
Helper T cells – activate both cytotoxic T cells and B cells
These four kinds of WBC interact to remove pathogens from the body.23
Imagine that you have just come down with the flu. You have inhaled the
influenza viruses, but they were not trapped by mucus in the respiratory tract.
The viruses have begun to infect and kill your cells.
At this point, macrophages begin to engulf and destroy the viruses.
An infected body cell will display antigens of an invader on its surface.
An antigen is a substance that triggers an immune response.
Antigens typically include proteins and other components of viruses or pathogen
cells present on the cell surface.
WBCs of the immune system are covered with receptor proteins that respond to
infection by binding to specific antigens on the surfaces of the infecting microbes.
These receptors recognize and bind to antigens that match their particular shape.
Immune response has two main parts
Two distinct processes work together in an immune response.
B cell response - a passive defense that aids the removal of
pathogens from the body.
T cell response – an active, cell-mediated defense that involves
the destruction of pathogens by cytotoxic T cells.
Both the T cell response and B cell response are regulated by
helper T cells.
Continued : Immune response has two main parts
Step 1: When a virus infects body cells, the infected cells display the viral antigen
on their surface.
Step 2: Macrophages engulf the virus and display the viral antigen on their
Step 3:Receptor proteins on helper T cells bind to the viral antigen displayed by
the macrophages. The macrophages release a protein called interleukin-1.
Step 4: Interleukin-1 activates helper T cells, but helper T cells do not attack
pathogens directly. Instead, helper T-cells activate cytotoxic T cells and B
cells. Stimulation by interleukin-1 causes helper T cells to release
interleukin-2. Interleukin-2 stimulates further division of helper T cells
and cytotoxic T cells, amplifying the body’s response to the infection.
Continued : Immune response has two main parts
Step 5: Interleukin-2 released by helper T cells also activates B cells.
When activated by interleukin-2, B cells divide and develop into
plasma cells. Plasma cells are cells that release special defensive proteins
into the blood. These specialized proteins are called antibodies. An
antibody is a Y shaped molecule that is produced by plasma cells upon
exposure to a specific antigen and that can bind to that antigen.
Step 6: Plasma cells divide repeatedly and make large amounts of
antibodies. Plasma cells either release antibodies into the
bloodstream or attach them directly to the virus. Antibodies bind to the
viral antigen on the virus and on infected cells. Antibodies mark the virus
and infected cells for destruction.
Continued : Immune response has two main parts
Step 7: When a plasma cell encounters a virus with an antigen that
matches its antibodies, it binds to the virus. This causes other
viruses to stick together, forming a clump that can be easily identified and
destroyed by macrophages.
Step 8: With the help of antibodies and plasma cells, cytotoxic T cells
destroy infected cells by puncturing the cell membrane of the
infected cells. How do cytotoxic T cells recognize antigens? Your body
makes millions of different T cells, each with receptor proteins that bind
to a specific antigen. Receptor proteins on cytotoxic T cells bind to the
viral antigen displayed by infected cells. For example, any of your body’s
cells that bear traces of an influenza virus will be destroyed by cytotoxic T
cells with receptor proteins that bind to the antigen of that virus.
Immune System Disorders
Hypersensitivity (Allergy): An abnormal response to
Four Types of Hypersensitivity Reactions:
• Type I (Anaphylactic) Reactions
• Type II (Cytotoxic) Reactions
• Type III (Immune Complex) Reactions
• Type IV (Cell-Mediated) Reactions
Type I (Anaphylactic) Reactions
• Occur within minutes of exposure to antigen
• Antigens combine with IgE antibodies
• IgE binds to mast cells and basophils, causing them to undergo
degranulation and release several mediators:
• Histamine: Dilates and increases permeability of blood vessels (swelling
and redness), increases mucus secretion (runny nose), smooth muscle
• Prostaglandins: Contraction of smooth muscle of respiratory system and
increased mucus secretion.
• Leukotrienes: Bronchial spasms.
• Anaphylactic shock: Massive drop in blood pressure. Can be fatal
Type II (Cytotoxic) Reactions
• Involve activation of complement by IgG or IgM binding to an
• Antigenic cell is lysed.
• Transfusion reactions:
• ABO Blood group system: Type O is universal donor.
Incompatible donor cells are lysed as they enter bloodstream.
• Rh Blood Group System: 85% of population is Rh positive.
Those who are Rh negative can be sensitized to destroy Rh
positive blood cells.
•Hemolytic disease of newborn: Fetal cells are destroyed by
maternal anti-Rh antibodies that cross the placenta.
Type III (Immune Complex) Reactions
• Involve reactions against soluble antigens circulating in serum.
• Usually involve IgA antibodies.
• Antibody-Antigen immune complexes are deposited in
organs, activate complement, and cause inflammatory
• Glomerulonephritis: Inflammatory kidney damage.
• Occurs when slightly high antigen-antibody ratio is present.
Type IV (Cell-Mediated) Reactions
• Involve reactions by TD memory cells.
• First contact sensitizes person.
• Subsequent contacts elicit a reaction.
• Reactions are delayed by one or more days (delayed type
• Delay is due to migration of macrophages and T cells to site of foreign
• Reactions are frequently displayed on the skin:
itching, redness, swelling, pain.
• Tuberculosis skin test
• Poison ivy
• Latex in gloves and condoms (3% of health care workers)
• Anaphylactic shock may occur.
Some Diseases of Immune System
• Allergic Contact Dermatitis Response to Poison Ivy Hapten
• Grave’s Disease:
• Myasthenia gravis:
• Systemic Lupus Erythematosus:
• Rheumatoid Arthritis:
• Insulin-dependent (Type I or Juvenile) Diabetes Mellitus:
• Acquired Immunodeficiency Syndrome (AIDS)
Type of Cell Function Location in the Body
Macrophage Ingests and kills pathogens Spleen, lungs, blood, lymph,
Neutrophil Engulfs and destroys pathogens Bloodstream, infection sites
Natural Killer Cell Punctures infected cells Infected cells
Helper T Cell Activates cytotoxic T and B cells Bloodstream, infection sites
Cytotoxic T Cell Punctures infected cells Infection sites
B Cell Labels invaders for destruction
By Macrophages Infection sites
Plasma Cell Releases antibodies Bloodstream
Memory Cell Protects against defeated
Many of the body’s most effective defenses are nonspecific.
•Nonspecific defenses include physical barriers such as the skin,
phagocytic cells, killer cells, and the complement proteins.
•Inflammatory response aids the mobilization of defensive cells
at infected sites.
Specific immune defenses require the recognition of antigens.
•Lymphocytes called B cells secrete antibodies and produce the humoral
response; lymphocytes called T cells are responsible for cell-mediated
T cells organize attacks against invading microbes.
• T cells only respond to antigens presented to them by macrophages
or other antigen-presenting cells together with MHC proteins.
• Cytotoxic T cells kill cells that have foreign antigens presented
together with proteins.
B cells label specific cells for destruction.
1. The antibody molecules consist of two heavy and two light polypeptide
regions arranged like a “Y”; the ends of the two arms bind to antigens.
2. An individual can produce a tremendous variety of different antibodies
because the genes which produce those antibodies recombine
3. Active immunity occurs when an individual gains immunity by prior
exposure to a pathogen; passive immunity is produced by the transfer
of antibodies from one individual to another.
All animals exhibit nonspecific immune response but specific
ones evolved in vertebrates.
•The immune system evolved in animals from a strictly nonspecific
immune response in invertebrates to the two-part immune defense
found in mammals.
The immune system can be defeated.
Flu viruses, trypanosomes, and the protozoan that causes malaria are
able to evade the immune system by mutating the genes that produce
their surface antigens. In autoimmune diseases, the immune system
targets the body’s own antigens.
Source: The Immune System . Johnson, Raven. 2001. Biology: Principles
and Explorations. Holt, Rinehart and Winston. Pages 931 - 937