DEFENCE MECHANISM

1. Subject: Microbiology
Faculty: Waheed Ahmed Mugheri,
Nursing Lecturer Sindhu College
Of Nursing Khairpur, Post-RN
BSc.N D.U.H.S Karachi.

2. At the end of this session…….
 The students will be able
to…
 To know about body
defense system.
 To know about Immune
system.
 To know about different
types of immunity.
 To know about different
lines of defense.
mechanism.
 To know about some
terminologies.

3. Define: Defense Mechanism
It is defined as body fights against
diseases by keeping things out of
your body that are foreign bodies
and also maintain physical health.
Your primary defense against
pathogenic germs are physical
barriers like your skin.
Our body is also produce
pathogen-destroying chemicals,
like lysozyme, found on parts of
your body without skin, including
your tears, saliva, and mucus
membranes.

4. Immune System
 The immune system is a network of
cells, tissues, and organs that work
together to defend the body against
attacks by “foreign” invaders.
 The reaction by the immune
system to antigens (substances
such as bacteria and viruses) that
the body recognizes as foreign is
called immune response.
 The immune system protects the
body from possibly harmful
substances by recognizing and
responding to antigens.

5. Some Important Terminologies…..
 Immunity
 Antigen
 Pathogen
 Antibodies
 Vaccine
 Immunization
 Phagocytosis

6. Terminologies
Immunity: It is the ability of an
organism to resist a particular infection or
toxin by the action of specific antibodies
or sensitized white blood cells.
Antigen: It is a toxin or other foreign
substance which induces an immune
response in the body, especially the
production of antibodies.
E.g. Virus, Bacteria, fungi, protozoa &
parasite.
Pathogen: A pathogen is usually defined
as a harmful microorganisms which
causes diseases to human or host.

7. Conti….
 Antibodies: A protein made by plasma
cells (a type of white blood cell) in response
to an antigen (a substance that causes the
body to make a specific immune response).
Immunization: A process by which a
person becomes protected against a disease
through vaccination. This term is often used
interchangeably with vaccination.
Vaccine: It is an antigenic substance, which
used to stimulate the production of
antibodies and provide immunity against
one or several diseases, prepared from the
causative agent of a disease, either killed or
live form.

8. Conti….
Phagocytosis: It is a process by which
certain living cells called phagocytes
ingest or engulf other cells or particles.
The phagocyte may be a free-living
one-celled organism, such as an
amoeba, or one of the body cells, such
as a white blood cell.

9. Main Parts of Immune System
 The main parts of the immune system are: white
blood cells, antibodies, the complement system,
the lymphatic system, the spleen, the thymus, and
the bone marrow.

10. Types of immunity

11. Conti……

12. Conti….

13. Innate Immunity
Innate or nonspecific: It is defined as the
defense system with which we were born. It
protects us against all antigens. Innate
immunity involves barriers that keep
harmful materials from entering your body.
 Immunity that is naturally present and is
not due to prior sensitization to an antigen.
In the innate immune response, these
include macrophages, neutrophils,
eosinophils, basophils, mast cells, and
dendritic cells.

15. Physical Parameters/Barriers
Fish scale: A fish scale is a small rigid
plate that grows out of the skin of a
fish. The skin of most fishes is covered
with these protective scales.
Mucous: The mucosal immune
system is the largest component of the
entire immune system, having evolved
to provide protection at the main sites
of infectious threat.
Skin: The skin has an immune
system that protects the body from
infection, cancer, toxins, and attempts
to prevent autoimmunity, in addition
to being a physical barrier against the
external environment.

16. Cellular Parameters/Barriers
 Cellular immunity: It occurs inside infected cells and is
mediated by T lymphocytes. The pathogen's antigens are
expressed on the cell surface
 Macrophages: Macrophages are scavengers whose job is to
engulf or eat up infecting germs and even infected cells.
Macrophages also help to overcome infection by secreting
signals that help activate other cell types to fight against
infections.
o Macrophages are a type of white blood cell (Monocyte) that
are part of your body's defense mechanism and also part of
the immune response in asthma.
 Granulocytes: As part of the immune response,
granulocytes migrate to the site of infection and release a
number of different effector molecules, including histamine,
cytokines, chemokines, enzymes and growth factors.
o It is a white blood cell with secretory granules in its
cytoplasm. E.g. Neutrophil, Basophil & Eosinophil.

17. Conti….
Neutrophil: are the most abundant type of
granulocytes and make up (40% to 70%) of all white
blood cells in humans.
 A type of immune cell that is one of the first cell
types to travel to the site of an infection. It helps in
fight against infections by ingesting microorganisms.
Basophil: Normally, basophils account for (0.5% to
1%) of your white blood cell count. They play a part
in "immune surveillance". This means they have the
ability to help detect and destroy some early cancer
cells. Another important function of basophils is that
they release the histamine in their granules during an
allergic reaction & asthma attack.
Eosinophils: (1.0 to 4.0 % )of your blood. It is a type
of disease-fighting white blood cell. This condition
most often indicates a parasitic infection, an allergic
reaction or cancer.

18. Conti….
Dendritic cells: These (DC) are among
the first cells to encounter pathogens or
damage in peripheral tissues and upon
activation, DCs migrate to lymph
nodes where they activate and educate T-
Lymphocyte cells to initiate the immune
response.
B-Cells: These are also known as B-
Lymphocyte cells. B-cells fight bacteria
and viruses by making Y-shaped proteins
called antibodies, which are specific to
each pathogen and are able to lock onto
the surface of an invading cell and mark it
for destruction by other immune cells.
o B cells are produced in stem cell of bone
marrow and also mature their.
o B cells fight bacterial infections specially.

19. Conti….
 T.Cells: These cells are part of the immune
system and develop from stem cells in the bone
marrow & mature in thymus. They help protect
the body from infection and may help fight
cancer & also called T lymphocyte
 The T cells respond to viral infections and
boost immune function of other cells.
 There are two types of T.Lymphocyte
1) Killer T cells (Recognizes and kills virally
infected cells and tumours) CD8 cells can
kill cancer cells and other invaders.
2) Helper T cells (helps in activation of B cells
to secrete antibodies and macrophages to
destroy ingested microbes, but they also help
activate cytotoxic T cells to kill infected
target cells.) CD4 cells lead the fight against
infections.
o Note: T & B Lymphocytes cells are part of
adaptive immunity

20. Conti…
 Mast Cells: A mast cell (also known as a mastocyte) is
a resident cell of connective tissue that contains many granules
rich in histamine and heparin. Specifically, it is a type of
granulocyte derived from the myeloid stem cell that is a part of
the immune and neuroimmune systems.
 Natural killer cells: (NCCs: Nonspecific Cytotoxic Cells) A
type of immune cell that has granules (small particles) with
enzymes that can kill tumor cells or cells infected with a virus.
A natural killer cell is a type of white blood cell & also known
as NK cell
o Heparin: It triggers their immune system and causes a
reaction where antibodies form and activate platelets, these are
tiny blood cells that clump together to form clots and stop
bleeds in your body.
o Histamine: It is produced by basophils and by mast cells
found in nearby connective tissues.
 Histamine is involved in the inflammatory response and has a
central role as a mediator of itching. As part of an immune
response to foreign pathogens.

21. Humoral Parameters/Barriers
 It is also called antibody-mediated immunity. With
assistance from helper T cells, B cells will differentiate
into plasma B cells that can produce antibodies against a
specific antigen. The humoral immune system deals with
antigens from pathogens that are freely circulating, or
outside the infected cells.
 Transferrin: It is also associated with the innate immune
system. It is found in the mucosa and binds iron, thus
creating an environment low in free iron that impedes
bacterial survival in a process called iron withholding.
o Transferrin: A plasma protein that transports iron
through the blood to the liver, spleen and bone marrow.
 Lysozyme: It is a cornerstone of innate immunity. The
degradation and lysis of bacteria by Lysozyme enhance
the release of bacterial products, including PG, that
activate pattern recognition receptors in host cells.
o Lysosome enzymes are made by proteins from the
endoplasmic reticulum and enclosed within vesicles by
the Golgi apparatus.

22. Conti….
Lectins: They are known to play
important roles in the innate immune
system. It helps mediate the first-line
defense against invading
microorganisms.
Cytokines: Cytokines are small proteins
that are crucial in controlling the growth
and activity of other immune system cells
and blood cells. When released, they
signal the immune system to do its job.

23. Conti….
Compliments: The complement system
helps or “complements” the ability of
antibodies and phagocytic cells to clear
pathogens from an organism. It is part of the
innate immune system. The complement
system consists of a number of small
proteins found in the blood, made by the
liver.
o Functions of the complement system:
1) The activation of inflammation.
2) The opsonization (labeling) of pathogens
and cells for clearance/destruction.
3) The direct killing of target cells/microbes
by lysis.

25. Define Antibodies
These are made up of protein by plasma
cells (a type of white blood cell) in response
to an antigen (a substance that causes the
body to make a specific immune response).
Each antibody can bind to only one specific
antigen.

26. Types of Antibodies
 Following are the types
of antibodies:
1) Immunoglobin (IgG).
2) Immunoglobin (IgM).
3) Immunoglobin (IgA).
4) Immunoglobin (IgE).
5) Immunoglobin (IgD).

27. Conti….
Immunoglobin.G:
It is the most abundant antibody isotype in the blood (plasma),
accounting for 70-75% of human immunoglobulins (antibodies).
IgG detoxifies harmful substances and is important in the
recognition of antigen-antibody complexes by leukocytes and
macrophages. IgG is transferred to the fetus through the placenta
and protects the infant until its own immune system is
functional.
Immunoglobin.M:
It usually circulates in the blood, accounting for about 10% of
human immunoglobulins. IgM has a pentameric structure in
which five basic Y-shaped molecules are linked together. B cells
produce IgM first in response to microbial infection/antigen
invasion.
Although IgM has a lower affinity for antigens than IgG, it has
higher avidity for antigens because of its pentameric/hexameric
structure. IgM, by binding to the cell surface receptor, also
activates cell signaling pathways.

28. Conti….
Immunoglobin.A:
IgA is abundant in serum, nasal mucus, saliva, breast
milk, and intestinal fluid, accounting for 10-15% of
human immunoglobulins. IgA in breast milk protects
the gastrointestinal tract of neonates from
pathogens.
Immunoglobin.E:
IgE is present in minute amounts, accounting for not
more than 0.001% of human immunoglobulins. Its
original role is to protect against parasites. In regions
where parasitic infection is rare, IgE is primarily
involved in allergy.
Immunoglobin.D:
IgD accounts for less than 1% of human
immunoglobulins. IgD may be involved in the
induction of antibody production in B cells, but its
exact function remains unknown.

29. Difference B/W Adaptive & Innate
Immunity
Innate Immunity Adaptive Immunity
It is basic resistance & present by birth, also
first line defense against infections.
This develops during life time. In this
immunity present after birth by naturally &
artificially.
Prevents the entry of pathogen or acts
within hours of antigen appearance in the
body.
Antigen specific immune response and
antigen recognition by this system, makes
immune cells specifically designed to attack
that antigen.
First line defense, Physical barriers( Skin,
mucous linings, saliva, tears, stomach)
Immune cells ( NK cells, macrophages,
neutrophils, dendritic cells, mast cells), that
attacks foreign cells in the body.
T & B lymphocytes, antibodies, classical
complement pathway.

30. Continue
Contact or exposure with antigen or
antigen is not essential (Antigen
independent).
Contact or exposure with pathogen or
antigen is essential (Dependent).
Rapid response with in hours, effector
molecules (Cytokines)
Slow response takes days/weeks, but may be
long lasting and also life long, Effector
molecules (Antibodies).
No immunologic memory similar response
on repeated exposure.
Immunologic memory, future response
against a specific antigen is more efficient.
Innate immunity is involved in all levels of
immune response.
Adaptive response is mounted when innate
response signals for serious infection.

31. Difference B/W Humoral and
Cell mediate Immunity

33. Define Hypersensitivity
 Hypersensitivity: It is also called
hypersensitivity reaction or
intolerance. Refers to undesirable
reactions produced by the normal
immune system, including
allergies and autoimmunity.
 They are usually referred to as an
over-reaction of the immune
system and these reactions may be
damaging and uncomfortable.

34. Types of hypersensitivity:
 The four types of hypersensitivity are:
 Type I: reaction mediated by IgE antibodies.
 Type II: cytotoxic reaction mediated by IgG or IgM
antibodies.
 Type III: reaction mediated by immune complexes.
 Type IV: delayed reaction mediated by cellular
response.


35. Immediate Hypersensitivity
 Immediate hypersensitivity (type I) is also
known as immediate contact urticaria and
the reaction occurs very rapidly. Common
causes include insect bites and ingested
peanuts. It is mediated by IgE antibodies,
which bind to the surface of mast cells.
 It is an allergic reaction provoked by re-
exposure to a specific type of antigen referred
to as an allergen.

36. Delayed Hypersensitivity
 Delayed-type hypersensitivity (DTH) is defined as the
recruitment of T cells into tissues to be activated
by antigen-presenting cells to produce cytokines
that mediate local inflammation. CD8+ T cells are
now known to mediate DTH responses in allergic
contact dermatitis, drug eruptions, asthma, and
autoimmune diseases.

38. Define Resistance
 It is defined as the natural or genetic ability of
an organism to avoid or repel attack by biotic
agents (pathogens, pests, parasites, etc.) or to
withstand the effects of abiotic agents.

39. Define Susceptibility
 It is defined as the quality or state of being
susceptible especially : lack of ability to resist
some extraneous agent (such as a pathogen
or drug)
 Susceptibility is being easily affected by
something.
 E.g: Susceptibility is having a very weak
immune system which causes a person to
frequently get colds.

41. Role Of Memory, Tolerance &
Specificity
 Memory: Memory is defined by the persistence of specific
lymphocytes and antibody-producing plasma cells rather than
that of antigen to induce continuous lymphocyte activation.
• E.g: When an individual recovers from chickenpox, the body
develops a memory of the infection that will specifically protect
it from the causative agent, the varicella-zoster virus, if it is
exposed to the virus again later.
 Tolerance: It is a state of unresponsiveness of the immune
system to substances or tissue that have the capacity to elicit an
immune response in a given organism. Tolerance is the
prevention of an immune response against a particular antigen.
• E.g: Induced tolerance is a deliberate manipulation of the
immune system to avoid the rejection of transplanted organs or
to provide protection from allergic reactions.

42. Conti….
 Specificity: It is defined as the quality or condition of
being specific, such as the condition of being peculiar
to a particular individual or group of organisms host
specificity of a parasite.