Objective
Students will be able to:
explain what pathogens are and how they
can infect the human body.
identify and describe the parts of the
immune system and explain how they work
to protect our body.
Skin is not a part of the immune
system.
Fever is a negative side effect of an
infection
• The skin is the body’s first line of defense.
Without the skin, pathogens would have free
access.
• A fever is the body’s way of fighting infection
by creating an inhospitable environment for
infectious agents.
• Homeostasis is the bodies attempt to maintain
a consistent internal environment
IMMUNE SYSTEM
• is made up of a network of cells, tissues and
organs that work together to protect the
body
• It attacks organisms and substances that
invade body systems and cause disease
through a series of steps called immune
response
• One of the important cells involved are
white blood cells (also known as
leukocytes)
Pathogen VS Antigen
Pathogen is an infectious agent that may cause a
disease. Virus, bacteria, fungus and other
microorganisms are often pathogenic.
Antigen is a molecule capable of causing the
immune system to produce antibodies against it.
Antigens are usually polysaccharides, lipids or
peptides. Antigens are molecules found on the
surface of pathogens and are specific to that
pathogen. E.g. hemagglutinin (influenza virus)
IMMUNE SYSTEM
Our white blood cells are stored in different places in
the body, which are referred to as lymphoid
organs. These include the following:
• Thymus — a gland between the lungs and just
below the neck.
• Spleen — an organ that filters the blood. It sits in
the upper left of the abdomen.
• Bone marrow — found in the center of the bones,
it also produces red blood cells.
• Lymph nodes — small glands positioned
throughout the body, linked by lymphatic vessels.
IMMUNITY
Everyone's immune system is different but, as a general
rule, it becomes stronger during adulthood as, by this
time, we have been exposed to more pathogens and
developed more immunity.
That is why teens and adults tend to get sick less often
than children.
Once an antibody has been produced, a copy remains in
the body so that if the same antigen appears again, it
can be dealt with more quickly.
TYPES OF IMMUNITY
Innate Immune Adaptive Immune
Response Response
TYPES OF IMMUNITY
Innate immunity
-includes the external barriers of our body — the first
line of defense against pathogens — such as the skin
and mucous membranes of the throat and gut.
The innate immune system is always general, or
nonspecific, meaning anything that is identified as
foreign or non-self is a target for the innate immune
response. The innate immune system is activated by the
presence of antigens and their chemical properties.
TYPES OF IMMUNITY
Adaptive (acquired) immunity
As we are exposed to diseases or get vaccinated,
we build up a library of antibodies to different
pathogens. This is sometimes referred to as
immunological memory because our immune
system remembers previous enemies.
Pathogens
(such as bacteria,
fungi, and viruses)
INNATE IMMUNITY Barrier defenses:
(all animals) Skin
• Recognition of traits shared Mucous membranes
by broad ranges of Secretions
pathogens, using a small Internal defenses:
set of receptors Phagocytic cells
• Rapid response Natural killer cells
Antimicrobial proteins
Inflammatory response
ADAPTIVE IMMUNITY Humoral response:
(vertebrates only) Antibodies defend against
• Recognition of traits infection in body fluids.
specific to particular
pathogens, using a vast Cell-mediated response:
array of receptors Cytotoxic cells defend
against infection in body cells.
• Slower response
TERMS
Self refers to particles, such as proteins and other
molecules, that are a part of, or made by, your body.
Non-self refers to particles that are not made by
your body, and are recognized as potentially
harmful. It can be bacteria, viruses, parasites, pollen,
dust, and toxic chemicals.
Cytokines are molecules that are used for cell
signaling, or cell-to-cell communication.
Chemokines are a type of cytokines that are
released by infected cells in order to initiate an
immune response
Innate Immunity of Invertebrates
In insects, an exoskeleton made of chitin forms the
first barrier to pathogens
The digestive system is protected by a chitin-based
barrier and lysozyme, an enzyme that breaks
down bacterial cell walls
Hemocytes circulate within hemolymph and carry
out phagocytosis, the ingestion and digestion of
foreign substances including bacteria
Innate Immunity of Vertebrates
The immune system of mammals is the
best understood of the vertebrates
Innate defenses include barrier defenses,
phagocytosis, antimicrobial peptides
Additional defenses are unique to
vertebrates: natural killer cells, interferons,
and the inflammatory response
Barrier Defenses
Barrier defenses include the skin and mucous
membranes of the respiratory, urinary, and
reproductive tracts
Mucus traps and allows for the removal of
microbes
Many body fluids including saliva, mucus, and
tears are hostile to many microbes
The low pH of skin and the digestive system
prevents growth of many bacteria
A white blood cell engulfs a microbe, then fuses
with a lysosome to destroy the microbe
Different types of phagocytic cells
Neutrophils are first cells to arrive at the
site of an infection; contain granules in
their cytoplasm
Macrophages are large, specialized cells
that recognize, engulf and destroy target
cells. It can also release cytokines in order
to signal and recruit other cells to an area
with pathogens
Lung Bone Lymph
Liver Brain intestine
Dendritic cells can identify threats and
act as messengers for the rest of the
immune system by antigen presentation;
stimulate development of adaptive
immunity
Mast cells mediate inflammatory responses
such as hypersensitivity and allergic
reactions
Eosinophils granulocytes responsible for
combating multicellular parasites and
certain infections in vertebrates
Basophils are also granulocytes that
attack multicellular parasites; release
histamine, much like mast cells.
Natural Killer cells (NK cells) do not
attack pathogens directly; destroy
infected host cells in order to stop the
spread of an infection; release
chemicals leading to cell death,
inhibiting the spread of virally infected
or cancerous cells
Antimicrobial Peptides and Proteins
Peptides and proteins function in innate defense
by attacking pathogens or impeding their
reproduction
Interferon proteins provide innate defense,
interfering with viruses and helping activate
macrophages
About 30 proteins make up the complement
system, which causes lysis of invading cells
and helps trigger inflammation
Inflammatory Responses
The inflammatory response, such as pain and
swelling, is brought about by molecules released
upon injury of infection
Mast cells release histamine, which triggers
blood vessels to dilate and become more
permeable
Activated macrophages and neutrophils release
cytokines, signaling molecules that enhance the
immune response
Pus, a fluid rich in white blood cells,
dead pathogens, and cell debris
from damaged tissues
Inflammation a response triggered by
damage to living tissues.
The inflammatory response is a defense
mechanism that help kill the pathogens
Fever is a systemic inflammatory response
triggered by pyrogens released by
macrophages and by toxins from
pathogens
Septic shock is a life-threatening condition
caused by an overwhelming inflammatory
response
Inflammation
CARDINAL SIGNS:
1. rubor (redness)
2. calor (increased heat)
3. tumor (swelling)
4. dolor (pain)
5. functio laesa (loss of function)
Redness is caused by the dilation of small blood vessels in
the area of injury.
Heat results from increased blood flow through the area
and is experienced only in peripheral parts of the body such
as the skin. Fever is brought about by chemical mediators
of inflammation and contributes to the rise in temperature at
the injury.
Swelling(also called edema) is caused primarily by the
accumulation of fluid outside the blood vessels.
Pain associated with inflammation results in part from the
distortion of tissues caused by edema, and it also is
induced by certain chemical mediators of inflammation.
Loss of function may result from pain that inhibits
mobility or from severe swelling that prevents movement in
the area.
How Does the Innate
Immune System Work?
ADAPTIVE IMMUNITY
ADAPTIVE IMMUNITY
The adaptive immune system consists of
lymphocytes and their products, including
antibodies.
The receptors of lymphocytes are much
more diverse than those of the innate
immune system, but lymphocytes are not
inherently specific for microbes, and they
are capable of recognizing a vast array of
foreign substances.
TYPES OF ADAPTIVE IMMUNITY
HUMORAL CELLULAR
mediated by B mediated by T
lymphocytes and lymphocytes and is
antibodies (also called responsible for
immunoglobulins, Ig) defense against
that protects against intracellular
extracellular microbes microbes.
and their toxins.
“antibody‐mediated
response”
TYPES OF LYMPHOCYTES
Lymphocytes begin their life in bone marrow.
Some stay in the marrow and develop into B
lymphocytes (B cells), others head to the
thymus and become T lymphocytes (T cells).
• B lymphocytes — they produce antibodies
and help alert the T lymphocytes.
• T lymphocytes — they destroy compromised
cells in the body and help alert other
leukocytes.
TERMS
MHC molecules- major histocompatibility complex,
group of genes that transport molecules to the cell,
where they present the antigen to T lymphocytes.
Class I MHC- present antigens to cytotoxic T cells
Class II MHC- present antigens to helper T cells
Interleukins- stimulatory molecules which is
secreted by helper T cells after it was divided
Antigens- any substance that evokes the
production of an antibody when introduced into
the body of an animal.
Humoral Immune Response
The response follows this chain of events:
I. Macrophages take up some of the antigen and
attach it to class II MHC molecules, which then
present the antigen to T helper cells.
II. The T helper cells bind the presented antigen,
which stimulates the T helper cells to divide and
secrete interleukins.
III. The interleukins in turn activate any B lymphocytes
that have also bound the antigen.
IV. The activated B cells then divide and secrete
antibodies.
V. Finally, the secreted antibodies bind the antigen and
help destroy it.
Plasma Cells
are activated B cells that secrete antibodies.
Memory Cells
Long-living plasma cells
retain a “memory” of a specific pathogen long after
an infection is over thus provides immunity to the
pathogen.
ANTIBODIES
• Also know as Immunoglobulin (Ig)
• Y-shaped protein that recognizes foreign
substance
• travel throughout the body in blood and lymph
Function of Antibodies
1. Agglutination: Enhances phagocytosis and
reduces number of infectious units to be dealt
with
2. Opsonization: Coating antigen with antibody
enhances phagocytosis
3. Neutralization: blocks adhesion of bacteria
and viruses to mucosa. Also blocks active site
of toxin
4. Activation of complement
5. Increases inflammation
6. Antibody dependant cell mediated cytotoxicity
IgG
Most abundant isotype in
serum (80%)
Cross placenta and play
important role in protecting
fetus
Moves to areas of inflammation
Help direct natural killer cells to
their targets
Vital in warding off both
bacterial and viral infections by
opsonization and neutralization
IgA
Most abundant Ab in the
body
Mainly found in sweat,
tears, saliva, mucus,
colostrum (first milk
secreted by a mother) and
gastrointestinal secretions
Provides passive immunity
to infants through mothers
breast milk
IgM
The largest antibody; found
in the lymph fluid and blood
First antibody produced
during an adaptive immune
response
Earliest immunoglobulin to
be synthesized by a fetus
at about 20 weeks of age
IgE
Mediate the immediate
hypersensitivity
reactions (hay fever,
asthma, hives,
anaphylactic shock)
provides protection
against parasitic worms
IgD
Found in blood, lymph
and especially on the
surface of mature B-
cells.
Acts as antigen
receptors
Able to cross the placenta into the fetus. Most
abundant type of antibody; protect against bacterial
and viral infections
What will happen if a person cannot produce
antibodies?
What will happen if you lose all of your
regulatory T cells?
