By Leah Ricci
Overview:

There are two major kinds of defense
that help an animal protect itself from
dangerous viruses, bacteria, and other
pathogens in food, water, and air
 The
first is call INNATE IMMUNITY which
is present before exposure to
pathogens and is effective from the
time of birth.
› It is a kind of defense that is mediated by
phagocytic cells, antimicrobial proteins,
the inflammatory response and natural
and killer cells
 The
second is ACQUIRED IMMUNITY
which develops after exposure to
inducing agents
› Acquired defenses can distinguish one
inducing agent from another by using
lymphocytes (white blood cells)
This picture show about B lympocyte. the
lympocyte is produce and mature in
bone marrow. it job is very importance
in producing antibodies to fight
pathogen( the foreign substances that
cause harm to our body)
Intact skin is a barrier that cannot
normally be penetrated by viruses or
bacteria but tiny abrasions may allow
their passage
 Mucous membranes lining digestive,
respiratory and genitourinary tracts bar
the entry of potentially harmful microbes

› Mucous membrane also produces mucus which
traps microbes and other particles

Secretions from the skin and mucous
membranes also contain antimicrobial
proteins
› This protein is present in saliva, tears, and
mucous secretions, lysozyme can destroy
susceptible bacteria as they enter the upper
respiratory tract of the openings around eyes

A bodies defenses depend mainly on
PHAGOCYTOSIS, the ingestion of
invading microorganisms by certain
types of white blood cells generically
referred to as phagocytes
› these cells produce certain antimicrobial
proteins and help initiate inflammation

Phagocytes attach to their prey via
surface receptors that bind to structures
found on many microorganisms but not
on normal body cells
› Microbes are destroyed by lysosomes in
two ways
 Nitric oxide and other toxic forms of oxygen
contained in the lysosomes may poison the
microbes.
 Or, lysozyme and other enzymes degrade
microbial components

Four types of white blood cells
(leukocytes) are phagocytic
› The most abundant are NEUTROPHILS which
make up about 60%-70% of all white blood
cells. Their life span is only a few days
because they tend to self destruct during
phagocytosis
› MACROPHAGES(big eaters) are large long-
lived cells that develop from monocytes,
which make up %5 of white blood cells.
Monocytes circulate in the blood for a few
hours then transform into macrophages in
the tissue
› EOSINOPHILS have low phagocytic
activity but are critical to defense
against multicellular parasitic
invaders
› DENDRITIC CELLS can ingest
microbes like macrophages do but
their main role is to stimulate the
development of acquired immunity

Two types of INTERFERON ( and β)
provide defense against viral infections

Other antimicrobial proteins include
about 30 serum proteins that make up
the COMPLEMENT SYSTEM
› In absence of infection these proteins are
inactive

Damage to the tissue can release
numerous chemical signals that triggers a
localized INFLAMMATORY RESPONSE
 When injured, mast cells release their histamine,
triggering dilation and increased permeability
of nearby capillaries
 Other cells send signals that promote blood
flow causing redness and heat of inflammation
 Blood clotting begins the repair process and
blocks microbes to other parts of the body
 Small proteins call CHEMOKINES direct the
migration of phagocytes and signal them to
increase production of microbe-killing
compounds

NK cells patrol the body and attack virusinfected body cells and cancer cells
› Once NK cells are attached to a virus-
infected cell or cancer cell the NK cell
releases chemicals that lead to the death of
the stricken cell be APOPTOSIS or
programmed cell death
Natural killer cells attacking a cancer cell
NK
NK
Cancer
Cell
The exoskeleton of insects, like the skin,
and mucous membranes of vertebrates,
provides an external barrier that can
prevent entry of intruders
 The insect equivalent to blood, the
hemolymph, contains circulating cells
called hemocytes


Recent research indicates that
invertebrates lack cells analogous to
lymphocytes the white blood cells
responsible for acquired specific
immunity in vertebrates

Invertebrates also have the ability to
respond more quickly to a particular
invader or foreign tissue the second time
it is encountered

As macrophages and dendritic cells
phagocytose microbes, the phagocytes
begin to secrete CYTOKINES, proteins
that help activate lymphocytes and
other cells of the immune system
› Any foreign molecule that is recognized by
lymphocytes and elicits a response from
them is called an ANTIGEN, large molecules
either proteins or polysaccharides
› A lymphocyte actually recognizes and binds
to just a small accessible portion of an
antigen called an EPITOPE
Cytokines
Cytokines

The vertebrate body is populated by two
main types of lymphocytes: B
lymphocytes (B cells) and T lymphocytes
(T cells)
› Both types circulate through the blood and
lymph in the lymph nodes, and other
lymphoid tissues

Each B CELL RECEPTOR for an antigen is
a Y-shaped molecule consisting of four
polypeptide chains: two identical HEAVY
CHAINS and two identical LIGHT CHAINS
› At the tips of the Y are light-and heavy-chain
variable (V) regions the remainder is the
constant (C) regions
Each T CELL RECEPTOR for an antigen
consists of two different polypeptide
chains ( and β) linked by a disulfide
bridge
 The receptors on the T cells recognize
small fragments of antigens called
MAJOR HISTOCOMPATIBILITY COMPLEX
(MHC)
 A new MHC molecule is transported
toward the plasma membrane, binds
with a fragment of protein antigen within
the cells and brings it to the cell surface,
a process called ANTIGEN PRESENTATION


Class II MHC MOLECULES are made by just a
few cell types mainly dendritic cells,
macrophages and B cells
› Dendritic cells, macrophages and B cells are
known as ANTIGEN-PRESENTING CELLS because
of their key role in displaying such internalized
antigens to another subgroup of T cells called
helper T cells

CLASS I MHC MOLECULES, found on almost
all nucleated cells of the body bind
peptides derived from foreign antigens that
have been synthesized within the cell
› Class I MHC molecules displaying bound peptide
antigens are recognized by a subgroup of T cells
called CYTOTOXIC T CELLS
T cell pushing B cell on a background
of collagen fibres in vitro
Lymphocytes that migrate from the
bone marrow to the THYMUS, a gland in
the thoracic cavity about the heart,
develop into T cells
 Lymphocytes that remain in the bone
marrow and complete their maturation
there become B cells

Lymphocyte Development

The selection of a B cell of T cell by an
antigen activates the lymphocytes
forming two clones of daughter cells
› One clone consists of a large number of
short lived EFFECTOR CELLS that combat the
same antigen
› The other clone consists of MEMORY CELLS,
long lived cells bearing receptors specific for
the same inducing antigen
 This antigen-driven cloning of lymphocytes is
called CLONAL SELECTION

PRIMARY IMMUNE RESPONSE, doesn't
peak until about 10 to 17 days
› During this time selected B cells generate
antibody-secreting effector B cells call
PLASMA CELLS and selected T cells are
activated to their effector forms
› If an individual is exposed again to the same
antigen the response is faster, 2-7 days. This is
called SECONDARY IMMUNE RESPONSE

The HUMORAL IMMUNE RESPONSE
involves the activation and clonal
selection of B cells resulting in production
of secreted antibodies

The CELL MEDIATED IMMUNE RESPONSE
involves the activation and clonal
selection of cytotoxic T cells which
directly destroy certain target cells

Central to this network of cellular
interactions is the HELPER T CELL which
responds to peptide antigens displayed
on antigen-presenting cells and in turn
stimulates the activation of nearby B
cells and cytotoxic T cells

A surface protein called CD4, present on
most helper T cells, binds the class II MHC
molecule
› This interaction helps keep the helper T cell
and the antigen-presenting cell joined which
activation of the helper T cell proceeds
Cytotoxic T cells eliminate body cells
infected by viruses or other intracellular
pathogens as well as cancer cells and
transplanted cells
 A surface protein called CD8, present on
most cytotoxic T cells, greatly enhances the
interaction between a target cell and a
cytotoxic T cell

› When a cytotoxic T cell is selected by binding to
class I MHC molecule-antigen complexes n an
infected body cell, the cytotoxic T cell is
activated and differentiates into an active killer

Immunity conferred by natural exposure
to an infectious agent is called ACTIVE
IMMUNITY because it depends on the
action of a persons own lymphocytes
and the resulting memory cells specific
for the invading pathogen
› Active immunity also can develop following
IMMUNIZATION, often called VACCINATION
helping induce an immediate immune
response and long-lasting immunological
memory
A red blood cells have A antigen
molecules on their surface, the A antigen
may be recognized as foreign if placed
in the body of another person
 B antigen is found on type B; both A and
B antigens are found on type AV; and
neither antigen is found on type O red
blood cells

 Blood
group antigens and related
bacterial epitopes are
polysaccharides which induce
immune responses in which no
memory cells are generated
› As a result anti-blood group antibodies
are always IgM (primary responses)
instead of IgG (secondary responses) this
helps in pregnancy because it IgM does
not cross the placenta and causes harm
to the fetus

Allergies are exaggerated (hypersensitive)
responses to certain antigens called
allergens
› The most common allergies involve antibodies of
the IgE class.
› Some of these antibodies attach by their tails to
mast cells present in connective tissues and later
when the allergen again enter the body they
attach to the antigen-binding sites of mast cellassociated IgE cross linking adjacent antibody
molecules
› This induces the mast cell to release histamines,
a process called degranulation
› an acute allergic response sometimes leads to
ANAPHYLACTIC SHOCK, a whole-body, life
threatening reaction that can occur within
seconds of exposure to an allergen

In some individuals the immune system
loses tolerance for self and turns against
certain molecules of the body causing
one of the many AUTOIMMUNE DISEASES
› Some diseases like Lupus, rheumatoid
arthritis, and insulin-dependent diabetes
mellitus can cause damage to the joints,
skin, or kidneys

The inability of the immune system to
protect the body from pathogens or
cancer cells that it should normally be
able to defeat reflects some sort of
deficiency in the system
This results from defects in the
development of various immune system
cells or defects in the production of
specific proteins such as IgA antibodies
or complement components
 In severe combined immunodeficiency
(SCID) both the humoral and cell
mediated branches of acquired
immunity fail to function

› The long-term survival or people with this
disease required a bone marrow transplant
Immune dysfunction that develops later
in life can be caused by exposure to a
number of agents
 Acquired immunodeficiency's range
from temporary states that may arise
from physiological stress to the
devastative AQUIRED
IMMUNODEFICIENCY SYNDROME, or
AIDS, which is caused by a virus

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