This document provides an extensive overview of immunology, detailing the body's defense mechanisms against foreign pathogens through innate and adaptive immunity. It explains key concepts such as antibody production, various types of immune responses, and the role of specific cells like T and B lymphocytes in mounting an immune response. The presentation further delves into definitions of immunological terms, mechanisms of action for innate defenses, and the processes involved in inflammation and phagocytosis.

1. BODY’S DEFENSE
MECHANISMS
MR MULUNDANO@kcn

2. INTRODUCTION
• The study of immunology, deals with host
defence reactions to foreign (nonself)
entities known as antigens, antigen
recognition molecules, and cell-mediated
host defence functions, especially as they
relate to immunity to disease,
hypersensitivity (including allergy),
autoimmunity, immunodeficiency, and
transplantation.
• This presentation presents the basic
principles of immunology, particularly as
they relate to response to infection.

3. • After the body is infected with a foreign
microorganism, it attempts to fight by
switching on a number of defense
mechanisms. There are a number of
responses involved such as;
inflammation, compliment system,
interferon, phagocytosis.

4. Top: The innate immune
system is characterized by
physiologic barriers to entry
of pathogenic organisms and
very fast host defense
responses.
Bottom: The adaptive
immune system consists of
cells displaying antigen
recognition molecules and
has the capacity for long-
term memory.

5. Specific objectives
• Definition of terms
• Explain types of defense mechanisms

6. Definitions
• Antibody (Ab): A protein produced as a result of
interaction with an antigen. The protein has the
ability to combine with the antigen that stimulated its
production.
• Antigen (Ag): A substance that can react with an
antibody. Not all antigens can induce antibody
production; those that can are also called
immunogens.
• Humoral immunity: Pertaining to immunity in a
body fluid and used to denote immunity mediated by
antibody and complement.
• Opsonisation - the process of coating
microorganisms with some of the proteins found in
plasma, to make them more easily phagocytosable.

7. Definitions
• Chemokines: Low-molecular-weight proteins that
stimulate leukocyte movement.
• Chemotaxis: A process whereby phagocytic cells are
attracted to the vicinity of invading pathogens.
• Complement: A set of plasma proteins that is the
primary mediator of antigen-antibody reactions.
• Cytolysis: The lysis of bacteria or of cells such as
tumor or red blood cells by insertion of the membrane
attack complex derived from complement activation.
• Cytotoxic T cell: T cells that can kill other cells, e.g,
cells infected with intracellular pathogens.
• Endotoxins: Bacterial toxins released from damaged
cells.

8. Definitions
• Immune response: Development of
resistance (immunity) to a foreign
substance (e.g, infectious agent). It can
be antibody-mediated (humoral), cell-
mediated (cellular), or both.
• T cell (also T lymphocyte): A thymus-
derived cell that participates in a variety
of cell-mediated immune reactions.

9. Types of defense mechanisms
• The Body defends itself against being
invaded and if successfully invaded, it
triggers other reactions that fight off the
invader.
A. Innate Immunity
B. Adaptive Immunity

11. A. Innate Immunity
• Innate immunity is the defence system
which you were born with.
• It protects you against all antigens.
(nonspecific)
• Innate immunity involves barriers that
keep harmful materials from entering
your body.

12. A. Innate Immunity cont’d.
•These barriers form the first line of
defence in the immune response.
Examples of innate non-humoral
immunity include:
• Cough reflex,
• Enzymes in tears and skin oils
• Mucus which traps bacteria and small
particles
• Skin,
• Stomach acid

13. A. Innate Immunity cont’d.
• Innate immunity also comes in a protein
chemical form, called innate humoral
immunity. Also know as Second line of
defence
• Examples include the body's
complement system and substances
called interferon and interleukin-1 (which
causes fever).
• If an antigen gets past these barriers, it is
attacked and destroyed by other parts of
the immune system.

14. A. Innate Immunity (non-humoral) cont’d.
a. The Skin
• Both the skin and the mucous membranes form
the first line of defence and belong to
nonspecific
• The intact skin provides a barrier through
which most micro-organism cannot pass, it
provides a good defence against invasion.
• Most microorganisms enter the body through a
break in the skin (cut).

15. A. Innate Immunity (non-humoral)
cont’d.
• The secretions of the skin by
sweat and sebaceous glands which
are acidity and have chemicals
which have anti-bacterial
properties tend to eliminate
pathogenic bacteria.

16. A. Innate Immunity (non-humoral) cont’d.
• b. Mucous Membranes/Surfaces
Bacteria are removed mechanically from
mucous membranes such as the nose,
mouth and vagina as mucus secretions
trap the organism.
• Bacteria in the respiratory tract are trapped
in the sticky secretion on the surface
(mucus) and then swept away by the
action of cilia, minute hair-like bodies
projecting from the cells lining the cavity.

17. A. Innate Immunity (non-humoral) cont’d.
•2.Secretions:
•Secretions act in 2 ways:
i) Mechanical action: e.g secretions of
the bronchi entrap organisms and these
are propelled away from the alveoli by
the action of cilia in the bronchi and
expelled tears by sneezing and
coughing in the eye.

18. A. Innate Immunity (non-humoral) cont’d.
ii) Chemical action:
•Secretions may be acidic like sweat
and gastric juice or strongly alkaline
like bile.

19. A. Innate Immunity cont’d.
• INNATE HUMORAL IMMUNITY.
1.Transferrin and lactoferrin: are
substances that tie up iron, thereby preventing
pathogens access to this essential mineral.
2. Fever: this augments host defence by
stimulating leukocytes to deploy and destroy
invaders, reducing available free plasma iron,
and inducing the production of interleukin IL-
1, which causes a rise in temperature and
proliferation, maturation, and activation of
lymphocytes in the immunologic response.

20. CONTD’
•Elevated body temperature also
slow down the rate of growth of
certain pathogens and can even kill
some especially fastidious
pathogens.

21. Innate Humoral Immunity cont’d.
• Elevated body temperature also
slow down the rate of growth of
certain pathogens and can even kill
some especially fastidious(difficult to
grow) pathogens.
3. Interferon’s: are small, antiviral
proteins that prevent viral
multiplication in virus-infected cells
and serve to limit viral infections.

22. Interferons

23. Innate Humoral Immunity cont’d.
4. Inflammation (inflammatory
reaction/process)
•Inflammation is the complex biological
response of vascular tissues to harmful
stimuli, such as pathogens, damaged
cells, or irritants.
•The damaged cells release chemicals
including histamine, bradykinin, and
prostaglandins.

25. Inflammation cont’d.
• These chemicals cause blood vessels to
leak fluid into the tissues, causing
swelling.
• This helps isolate the foreign substance
from further contact with body tissues.

26. Inflammation cont’d.
• The chemicals also attract white blood
cells called phagocytes that "eat" germs
and dead or damaged cells. This process
is called phagocytosis.
• Phagocytes eventually die. Pus is formed
from a collection of dead tissue, dead
bacteria, and live and dead phagocytes

27. Inflammation cont’d.
•Classic Signs of inflammation:
i. RUBOR- Reddish appearance
ii. CALOR- Hotness at the site
iii. TUMOR- Swelling at the site
iv. DOLOR- Pain at the site of injury

28. Inflammation cont’d.
• By surrounding the
area of infection with
plasma which often
contains phagocytes,
the infection may be
prevented from
spreading.
• Flow of fluid to and
from the area of
inflammation is largely
by lymph vessels.

29. Inflammation cont’d.
• Bacteria escaping
from the area will
usually enter the
lymph and will be
arrested at the
nearest lymph node.
• Secondary
inflammatory reaction
may take place
(lymphadenitis) but in
many cases the
infection will not
become generalised.

30. Inflammation cont’d.
•This inflammatory response of
the tissues tends to restrict the
spread of infection within the
body and in many cases to
overcome it at the cost of inner
area damage.
•If for some reason the inflammatory
response is deficient, the infection
will tend to become systemic and
much more serious

31. Innate Humoral Immunity cont’d.
• 5. Phagocytosis.
• The white blood cells, together with
certain tissue cells move towards the
bacteria and attempt to ingest them by a
process known as phagocytosis,
engulfment by phagocytes and
ingestion by lysosomes.

33. Innate Humoral Immunity cont’d.
6. Complement system:
•Complement system, Involves
approximately 30 different
blood proteins that interact in
a step-wise manner known as
the complement cascade, to
try and clear off any
pathogen the body comes in
contact with.

34. Consequence of activation of the
complement system:
• Initiation and amplification of
inflammation.
• Attraction and activation of leukocytes.
• Lysis of bacteria and other foreign cells.
• Increased phagocytosis by phagocytic
cells.
• These defences operate against a
variety of micro-organisms, because it
is not specific.

35. B. Adaptive Immunity
Aka: Acquired; specific

36. Types of immunity

38. B. Adaptive Immunity
• Adaptive immunity, which occurs after
exposure to an antigen (e.g., an
infectious agent) is specific and is
mediated by either antibody or lymphoid
cells.
• It can be;
• i) Natural (Active or Passive or
• ii) Artificial (Active or Passive).
• Third line of defence

39. B. Adaptive Immunity cont’d.
• Specific defence mechanism is a
complement to the function of
phagocytes and other elements of the
innate immune system.
• In contrast to innate defence mechanism,
specific defence mechanism allows for a
targeted response against a specific
pathogen.

40. B. Adaptive Immunity cont’d.
Only vertebrates have specific defence mechanism
responses.
Two types of white blood cells called lymphocytes
are vital to the specific defence mechanism
response.
Lymphocytes are produced in the bone marrow,
and mature into one of several subtypes. The two
most common are T cells and B cells.

45. B. Adaptive Immunity cont’d.
•The human body has B and T cells
specific to millions of different
antigens.
•An antigen is a foreign material
that triggers a response from T and
B cells.

47. B. Adaptive Immunity cont’d.
• We usually think of antigens as part of
microbes, but antigens can be present in
other settings.
• For example, if a person received a blood
transfusion that did not match his blood
type, it could trigger reactions from T and B
cells.
• T and B cells can mature and differentiate
into plasma cells that produce a protein
called an antibody.

49. Blood types

50. B. Adaptive Immunity cont’d.
PASSIVE IMMUNITY
• Passive immunity is transmitted by
antibodies or lymphocytes preformed in
another host.
• The passive administration of antibody. (in
antisera) against certain viruses (e.g.,
hepatitis B) can be useful during the
incubation period to limit viral multiplication,
e.g., after a needlestick injury to someone
who has not been vaccinated.

51. Passive Immunity cont’d.
•The main advantage of passive
immunization with preformed
antibodies is the prompt availability
of large amounts of antibody;
•Disadvantages are the;
oShort life span of these antibodies and
oPossible hypersensitivity reactions if
antibodies (immunoglobulins) from
another species are administered.

52. Passive Immunity cont’d.
• I. Naturally acquired passive immunity
• Here the antibody is obtained by the
child from the mother either across the
placenta or in breast milk.
• The human placenta allows maternal
antibodies to pass into the foetal
circulation.

53. Naturally acquired passive
immunity
• The baby is born having maternal
antibodies against the diseases to
which the mother is immune.
• This provides the baby with defence
immediately after birth.
• The antibodies do not persist.
• They disappear after a few months.

54. Passive Immunity cont’d.
• Artificially acquired passive immunity
• In here the antibody is obtained or protection
is derived from the injection (serum) of
prepared or readymade antibodies. e.g
administering preformed antibodies of rabies
vaccine following a rabies dog bite.

55. B. Adaptive Immunity cont’d.
Active Immunity
• Active immunity is induced after
contact with foreign antigens (e.g.,
microorganisms or their products).
• This contact may consist of clinical or
subclinical infection, immunization
with live or killed infectious agents or
their antigens, exposure to microbial
products (e.g., toxins, toxoids), or
transplantation of foreign cells.

56. Active Immunity cont’d.
• In all these instances the host actively
produces antibodies, and lymphoid cells
acquire the ability to respond to the antigens.
• Advantages of active immunity include;
• Long-term resistance (based on memory of prior
contact with antigen and
• The capacity to respond faster and to a greater
extent on subsequent contact with the same
antigen)
• Disadvantages include;
• The slow onset of resistance and the need for
prolonged or repeated contact with the antigen.

57. Naturally acquired active immunity
• This is the type of immunity which is
acquired in response to the entry of a live
pathogen into the body (i.e., in response
to an actual infection)
• It has long duration (has memory).
• Examples are typhoid fever, measles
and small pox.

58. Artificially acquired Active
immunity
• In here the antibody is obtained or protection
is derived from introducing antigens such as
vaccines which are live attenuated or dead
into the body and then the body produces
specific antibodies against them.
• Expanded Program of Immunization (EPI)
is aimed at stimulating the bodies of
children to produce specific antibodies against
the common childhood killer diseases such as
measles, poliomyelitis etc

59. Antibody isotypes of mammals
1. Immunoglobulin A or (IgA)
2. Immunoglobulin D or IgD
3. Immunoglobulin E or IgE
4. Immunoglobulin G or IgG
5. Immunoglobulin M or IgM

60. • Immunoglobulin A or (IgA) Found in mucosal areas, such
as the gut, respiratory tract and urogenital tract, and
prevents colonization by pathogens. Also found in saliva,
tears, and breast milk.
• IgD: Functions mainly as an antigen receptor on B cells that
have not been exposed to antigens. It has been shown to
activate basophils and mast cells to produce
antimicrobial factors.
• IgE: Binds to allergens and triggers histamine release from
mast cells and basophils, and is involved in allergy. Also
protects against parasitic worms.
• IgG: In its four forms, provides the majority of antibody-
based immunity against invading pathogens. The only
antibody capable of crossing the placenta to give
passive immunity to the foetus.
• IgM: Expressed on the surface of B cells and has very high
avidity (is a measure of the overall strength of binding of an
antigen with many antigenic determinants).
• Eliminates pathogens in the early stages of B cell
mediated (humoral) immunity before there is sufficient
IgG.

61. CONTD’
•This protein or antibody is
specifically targeted to a particular
antigen.
•However, B cells alone are not very
good at making antibody and rely on
T cells to provide a signal that they
should begin the process of
maturation.

62. CONTD’
•When a properly informed B cell
recognizes the antigen it is coded
to respond to, it divides and
produces many plasma cells.
• The plasma cells then secrete
large numbers of antibodies,
which fight specific antigens
circulating in the blood.

63. CONTD’
•T cells are activated when a
particular phagocyte known as
an antigen-presenting cell (APC)
(the APC-is a trigger for the various
elements of the specific immune
response) displays the antigen to
which the T cell is specific.

64. Other cells
•A subtype of T cell known as a T
helper cell performs a number of
roles.
•T helper cells release chemicals to
•Help activate B cells to divide into
plasma cells
•Call in phagocytes to destroy
microbes
•Activate killer T cells

66. CONTD’
•Once activated, killer T cells
recognize infected body cells and
destroy them.
• Regulatory T cells (also called
suppressor T cells) help to control
the immune response.
•They recognize when a threat has
been contained and then send out
signals to stop the attack.

67. Organs and Tissues of defence
mechanisms
• The cells that make up the specific
immune response circulate in the
blood, but they are also found in a
variety of organs.
• These immune tissues and organs
allow for maturation of immune cells,
trap pathogens and provide a place
where immune cells can interact with
one another and mount a specific
response.

68. CONTD’
•Organs and tissues involved in the
immune system include the thymus,
bone marrow, lymph nodes,
spleen, appendix, tonsils, and
Peyer’s patches (in the small
intestine).

69. The End