The document provides an overview of innate and adaptive immune responses, detailing the components and mechanisms involved in immunity. It explains the properties of innate immunity, which serves as the first line of defense, and outlines the adaptive immune system's specificity and memory, highlighting the roles of various immune cells such as B and T lymphocytes. It also discusses ways to induce immunity, including vaccination and natural antibody transfer.

1. INNATE & ADAPTIVE IMMUNE
RESPONSES
MUNDIA KANGONGWE,
Dip MLT, BSc BMS, MSc MM

2. LECTURE OBJECTIVES
• Define innate immunity and know the various
innate/natural mechanisms of immunity.
• Know the properties of innate immunity.
• Know the link between innate and adaptive immunity.
• Know what adaptive immunity is, it’s properties and
the two arms of adaptive immunity.
• Know the role of antigen receptors in an immune
response.
• Know the effector cells and mechanisms involved in
mounting an immune response by the two arms of
adaptive immunity.
• Understand ways of inducing immunity.

3. Innate Immunity
“Refers to various PHYSICAL, CHEMICAL, and
CELLULAR attributes that collectively represent
the first line of defense against infectious
disease.”

4. Components of innate immunity
Anatomic barriers
Physiologic barriers
Inflammatory mechanisms
Phagocytic mechanisms
Enzymes and soluble proteins
Microbial normal flora.

5. Properties of Innate Immunity
o Found in all multi-cellular organisms.
o Adaptive immunity is only in vertebrates.
o Uses ancient gene encoded receptors and
effectors.
o Provides protection against a wide variety of
pathogens.
o Distinguishes self from non-self well.
o Defects in innate immunity are very rare and
almost always lethal.

6. Properties of Innate Immunity
o Makes the first line of defence and predates
the adaptive immune response.
o Works independent of prior exposure.
o Thus, lacks memory response & it’s benefits.

7. 1. PHYSIOLOGIC BARRIERS
A. The Skin:
• The major line of defense is the skin, which when
intact, is impermeable to most infectious agents;
thus, when there is loss of skin, e.g. in burns,
infection becomes imminent.
Prevents microorganism from gaining access into the
body.
Fatty acids
Low pH (Lactic acid)
Antagonism by normal flora
Salt in sweat

8. 1. PHYSIOLOGIC BARRIERS
B. Mucous Membranes
Respiratory tract
oMucous
oHairs of the nares
oCilia
oCough reflex
GIT
oHydrolytic enzymes
oAcidity of the stomach
oProteolytic enzymes and macrophages (Small
intestines)

9. 1. PHYSIOLOGIC BARRIERS
B. Mucous Membranes
Urogenital
oWashing effect of urine
oAcidity of urine
oVaginal Lactic acid
oAntagonism by normal flora
Eye
oLysozyme
oTears and blinking effect

10. C. Microbial normal flora
• These are harmless bacteria found in/ on
the body e.g.
the intestinal tract
Urogenital tract.
Skin

11. • They suppress the growth of many potentially
pathogenic bacteria and fungi at superficial sites
by;
 Competing for attachment sites.
Competing for essential nutrients.
Production of inhibitory substances
Competing for gaseous requirements, etc.

12. Anatomical defenses
associated with tissue
surfaces

13. 2. CELLULAR COMPONENTS OF INNATE
IMMUNITY

14. A. Neutrophils
• Phagocyte with a characteristic nucleus &
cytoplasm.
• Carries out phagocytosis, intracellular killing,
inflammation and tissue damage.

15. A. Neutrophils
• Circulate in blood stream, highly motile.
• Extravasate into tissues via diapedesis
towards inflammation by chemotaxis.
• Attracted by cytokines (e.g. IL-8, IFNγ)
produced by epithelial cells and APCs.
• Rapid response- first cell to arrive during an
immune response.

16. A. Neutrophils
• Short lifespan (1-2 days).
• Terminally differentiated cells
• Involved in inflammation
• Has a greater killing power than MF

17. A. Neutrophils
Killing mechanisms
Phagocytosis
1. Oxygen Dependent:
o Hydrogen peroxide
o Reactive Oxygen species
2. Oxygen Independent:
o Lysozyme
o Lactoferrin
o perforins
o Others

18. B. Basophils
• Contains high affinity receptors for IgE, and
preformed granules that contain inflammatory
mediators including: histamine; heparin;
TNFα; chondroitin sulfate; neutral proteases;
and others.

19. C. Mast cells
• Mast cells can also secrete: cytokines to
induce inflammation; chemokines to induce
infiltration by monocytes and neutrophils,
leukotrienes to induce muscle contraction and
increase vascular permeability.
• Mast cells are capable of inducing an
inflammatory cascade.

20. D. Mononuclear Phagocytes
• Monocytes are immature circulatory forms
(1-6% WBCs).
• Migrate into tissues and are called
macrophages.
• Have Specialized names based on site
o Kidney (Mesangeal cells)
o Connective tissue (histiocytes)
o Bone (Osteoclasts)
o Liver (Kupffer cells)
o Brain (Microglial cells)

22. E. Macrophages
• Single nucleus.
• Abundant cytoplasm.
• Carries out phagocytosis and digest engulfed
material.

23. E. Macrophages
• Present in all tissues.
• Abundant in the spleen, lymph nodes and the
GIT.
• Upon activation Macrophages process Ag and
release cytokines (cell-cell communication) to
communicate with other cells of the immune
system.

24. E. Macrophages

25. F. Natural Killer cells (NK cells)
• Large cytotoxic cells (look like large
lymphocytes and contain granules).
• 10-15% of peripheral blood lymphocytes
• Kill virus-infected and tumor cells (low MHC I
expression).
• Also important in resistance to intracellular
infections with viruses or bacteria.

26. F. Natural Killer cells (NK cells)
• Do not secrete antibodies nor express T cell
receptors.
• Also called large granular lymphocytes (LGL)
• NK cells kill using perforin
• NK cells do not require a thymus for their
development but have several similarities to
activated CD8 T cells.
• Rapidly produce cytokines upon ligand
recognition.

27. F. Natural Killer cells (NK cells)
• NK Killing mechanisms
• Perforin; a cytolytic protein in the granules of
CD8 T-cells and NK cells.
• After degranulation, perforin inserts itself into
the target cell's plasma membrane, forming a
pore.

28. G. Dendritic Cells (DCs)
• DCs are highly migratory cells.
• Make up less than 1% of the total
mononuclear cells.
• Present in their immature form in all tissues.
• DCs act as peripheral sentinels, detecting, and
responding to antigen invasion.

29. G. Dendritic Cells (DCs)
• DCs are highly migratory cells.
• Make up less than 1% of the total
mononuclear cells.
• Present in their immature form in all tissues.
• DCs act as peripheral sentinels, detecting,
deciphering and responding to signs of
antigen invasion

30. G. Dendritic Cells (DCs)
• DCs then process antigen, move into lymphoid
organs where they activate T cells.
• As DCs migrate towards the lymph nodes, they
mature.
• They lose their capacity for endocytosis and
become more immunogenic (more dendrites
and expressing a higher number of co-
stimulatory & MHC peptide molecules).

31. The Adaptive Immune
Responses

32. Adaptive immune system
• The adaptive immune response is different from the
innate immune response in that it has specificity and
memory.
– Specificity – ability to recognize and respond to
particular targets.
– Memory – second exposure to the same organism
produces a larger and more rapid response than
occurred at the primary exposure.
• The adaptive immune response is much slower than
the innate immune response.

33. Adaptive immune system
• Lymphocytes are the effector cells of the adaptive immune
system.
• They display highly diverse receptors for antigen.
• Each cell has multiple copies of a receptor for a single antigen
only, and thus responds only to one antigen (Specificity).
• Antigens are molecules which are recognized by receptors on
lymphocytes, and elicit a specific immune response to that
antigen.
• Antigen presenting cells (APCs) collect antigens from infected
tissues, and carry to lymphoid tissues to display and activate
lymphoid cells.
• Cytokines act as messengers between cells of the immune
system.

34. Humoral and cell-mediated immunity
• The adaptive or specific immune response involves two
main lines of defence: humoral immunity and cell
mediated immunity.
– Humoral immunity involves B lymphocytes (B cells)
– Cell-mediated immunity involves T lymphocytes (T
cells).
• Both B cells and T cells are derived from stem cells in
the bone marrow, however they mature in different
parts of the body.
– B cells mature in the bone marrow then travel to
lymphatic tissues, especially the spleen and lymph
nodes.
– T cells mature in the thymus.

35. Cells of the immune system
Bone graft
Multipotential
stem cell
Hematopoietic
stem cell
Platelets
Macrophage
Erythrocytes
Eosinophil
Neutrophil
Megakaryocyte
Mast cell
Basophil
T lymphocyte
Natural killer cell
Dendritic cell
B lymphocyte
Lymphoid progenitor cell
Myeloid
progenitor
cell
Monocyte
Marrow
Bone

36. B Cells
• B cells work chiefly by secreting soluble substances
known as antibodies.
• There are 1000s of different B cells, each recognizes a
different antigen .
• Each antigen stimulates production of a single
specific antibody.
• When a B cell meets and interacts with a specific
antigen, the B cell becomes metabolically active and
begins to divide.

37. B Cell Development
• Over 5 x 107 B cells produced in bone marrow everyday.
• Only 10% of these enter circulation.
• 90% eliminated in Bone Marrow by “Negative selection
of B Cells.”
• B Cells released into circulation are Naïve B cells.
• Contact with specific antigen leads to arrest in secondary
Lymphoid tissues and activation.

38. B Cell Activation
• B Cell has Surface Immunoglobulin as B Cell
receptor (BCR).
• Naïve B Cell in circulation lasts only a few days.
• Naïve B Cell that binds antigen through surface
immunoglobulin becomes trapped in Lymphoid
tissue and is activated.

39. B Cell Activation
• Activated B Cell leads to cell proliferation,
clonal expansion and differentiation into:
Plasma cells (Secrete antibodies).
Memory B Cells- remain in lymphoid tissues
and are responsible for the immunity that
arises following infection or vaccination.

41. B Cell Activation Signals
• B Cell activation requires 2 signals and
Cytokines from T-helper cells.
• The signals are:
1. Binding of surface immunoglobulin to
antigen.
2. Cell-to-cell contact between B Cell and T-
helper cell.

42. 1. Binding of BCR to antigen
• Binding of surface Ig to antigen is the first signal.
– Antigen binds to surface Immunoglobulin on B cell
and this binding initiates activation of B Cell.
• Surface Ig-Ag complex is internalized into B Cell by
endocytosis and processed into Ag peptides.
• Ag peptides are cleaved by lysosomal enzymes into
short Ag peptides.

44. Binding of BCR to antigen…….
• Short peptides complexed to MHC class II
molecules.
• MHC II- Peptide complex transported and
expressed on B cell surface.
• MHC II- Peptide Complex presented to TH
Cell.

45. 2. Direct Cell-to-Cell Contact
● Direct contact between B Cell and TH cell.
● This cell-to-cell contact triggers TH cell to
secrete Cytokines (IL-2, IL-4, IL-5 and others).
● These cytokines in turn cause B cell activation.
• Activated B Cell expresses receptors for
Cytokines (IL-2, IL-4, IL-5 and others).

46. Direct Cell-to-Cell Contact……..
• Binding of Cytokines secreted by TH cell to
Cytokine receptors on B Cell helps proliferation
and differentiation of B Cell.
• Activated B Cell divides into;
– Plasma cells that produce antibodies.
– Memory B Cells.
• Antibodies are effector molecules of the Humoral
immunity.

48. Helper T cells
• Recognize antigens on the surface of white blood
cells, particularly macrophages (APC).
• Enlarge and form a clone of T helper cells.
• Secrete interferon and cytokines which stimulate B
cells and killer T cells.

49. Killer T cells
• Also called cytotoxic T cells.
• Destroy abnormal body cells e.g. virus infected or cancer cells.
• Stimulated by cytokines released by TH cells.
• Release perforins which form pores in target cells – this allows
water and ions in and leads to lysis of the target cell.
• Natural killer (NK) cells are another type of lymphocyte that acts in
a similar manner to cytotoxic T (TC)cells.
• Cytotoxic T cells need to recognize a specific antigen bound to self-
MHC markers, whereas natural killer (NK) cells will recognize and
attack cells lacking these. This gives NK cells the potential to attack
many types of foreign cells.

50. Killer Cells: cytotoxic T cells and NKs
Killer cell
Target-oriented
granules
Surface contact
Target cell

51. Memory T cells
• Can survive a long time and give lifelong
immunity from infection.
• Can stimulate memory B cells to produce
antibodies.
• Can trigger production of killer T cells.

52. Role of antigen receptors in the immune
response
• Both B cells and T cells carry customized receptor molecules that
allow them to recognize and respond to their specific targets.
• The B cell’s antigen-specific receptor that sits on its outer surface
is also a sample of the antibody it is prepared to manufacture; this
antibody-receptor recognizes antigen in its natural state.
• The T cell’s receptor systems are more complex. T cells can
recognize an antigen only after the antigen is processed and
presented in combination with a special type of major
histocompatibility complex (MHC) marker.
• Killer T cells only recognize antigens in the grasp of Class I MHC
markers, while helper T cells only recognize antigens in the grasp of
Class II MHC markers. This complicated arrangement assures that T
cells act only on precise targets and at close range.

53. Role of cytokines in immune response
• Cytokines are diverse and potent chemical messengers secreted by the cells of
your immune system. They are the chief communication signals of your T cells.
Cytokines include interleukins, growth factors, and interferons.
• Lymphocytes, including both T cells and B cells, secrete cytokines called
lymphokines, while the cytokines of monocytes and macrophages are dubbed
monokines. Many of these cytokines are also known as interleukins because
they serve as a messenger between white cells, or leukocytes.
• Interferons are naturally occurring cytokines that may boost the immune
system’s ability to recognize cancer as a foreign invader.
• Binding to specific receptors on target cells, cytokines recruit many other cells
and substances to the field of action. Cytokines encourage cell growth, promote
cell activation, direct cellular traffic, and destroy target cells--including cancer
cells.
• When cytokines attract specific cell types to an area, they are called
chemokines. These are released at the site of injury or infection and call other
immune cells to the region to help repair damage and defend against infection.

54. WAYS OF INDUCING IMMUNITY
Vaccination
 The term vaccination is derived from the Latin
word ‘vaccinus’ meaning ‘from cows’.
 Edward Jenner, an English physician, noticed that
dairymaids who frequently contracted cowpox
were immune to smallpox.
 He experimentally infected a young boy with
cowpox and the boy eventually became immuned
to smallpox.
 The aims of vaccination are to induce memory in
T and/or B lymphocytes through the injection of
a non-virulent antigen preparation.

55. Ways in which protective immunity
can be acquired or induced.
• Immunity can be transferred from
immunized individual to unimmunized
individual.
• Immunity confered on an individual can
either be in a form of active acquired
immunity or passive acquired immunity.

56. 1. Naturally acquired active
immunity.
• An individual is exposed to a pathogen by
natural means.
• The exposure is not intentional.
• An individual’s immune system takes part in
producing antibodies.
Example:
• when individual is exposed to an infectious
microbe & develops clinical disease.

57. 2. Artificially acquired active
immunity
• An individual is exposed to a pathogen by
artificial means.
• The exposure is intentional/deliberate-
vaccination.
• Individual actively responds to an antigen by
producing antibodies against the pathogen.
Example:
• Administration of attenuated microorganisms.

58. 3. Naturally acquired passive
immunity
• Transfer of antibodies to an individual by natural means.
• Examples:
• Passage of maternal antibodies from the mother to the
fetus through the placenta; thus conferring protection
to the fetus/newly born baby.
• Breastfeeding (antibodies passing through colostrum
milk).

59. 4. Artificially acquired passive immunity
• Transfer of antibodies to an individual by
artificial means.
• Examples:
• Administration of antibodies from immunized
animals as the treatment for lethal infections
such as tetanus and rabies.
• It’s a useful method for conferring immunity
rapidly.

60. Immunizing agents
Immunizing agents
Antisera/anti-toxins
immunuglobulins
vaccines