The innate immune system provides the body's first line of defense against pathogens through physical, chemical, and cellular barriers. It responds quickly but non-specifically. Components of innate immunity include physical barriers like skin, mucous membranes, and microbiota; physiological barriers like low pH and natural killer cells; cellular barriers comprising phagocytes and cytokines; and inflammatory responses. Pattern recognition receptors expressed by innate immune cells recognize pathogen-associated molecular patterns and damage-associated molecular patterns to detect and respond to infections.

1. PROPERTIES OF IMMUNE SYSTEM
(Innate & Adaptive)
Presenter: Ussi Khamis
Facilitator: Prof. Lyamuya

2. Outline
• Objectives
• Introduction
• Innate immunity
• Adaptive immunity

3. Objectives
• At the end of this presentation we should be able to
describe;
 Innate immunity and its components
 Acquired immunity and its components

4. Learning Outcomes
• Explain the components & characteristics of innate and
adaptive immune responses.
• Describe effector mechanisms used by the innate
immune system, the cells and molecules involved in
each mechanism,
• Discus mechanisms used by the adaptive immune
system, and the cells involved.
• Explain the deference between the innate immune
response and adaptive immune response
• Describe how innate responses help to ensure that an
effective adaptive immune response is generated for a
specific pathogen.

5. INTRODUCTION
• Defense against microbes is mediated by sequential and
coordinated responses, that are called innate and
adaptive immunity.
• Innate immunity (natural/native immunity) is essential for
defending against microbes in the first few hours or days
of infection, before adaptive immune responses have
developed.
• Innate immunity is mediated by mechanisms that are in
place even before an infection occurs (hence innate) and
that facilitate rapid responses to invading microbes.

6. Introduction..
• In contrast, there are other immune responses that are
stimulated by exposure to infectious agents and increase
in magnitude and defensive capabilities with each
successive exposure.
• Because this form of immunity develops as a response
to infection and adapts to the infection, it is called
adaptive immunity (specific/acquired immunity).
• The adaptive immune system recognizes and reacts to a
large number of microbial and nonmicrobial substances,

7. INTRODUCTION

8. Introduction…
Immune System
Innate
(Non-specific)
Adaptive
(Specific)
Cellular
Components
Humoral
Components
Cellular
Components
Humoral
Components
8
Physical
components

9. INNATE IMMUNE
• Innate immunity is mediated by mechanisms that are in
place even before an infection occurs (hence innate) and
that facilitate rapid responses to invading microbes.
• Charactorised by
 Immediate response to the pathogen
 Doesn't confer long-lasting protective immunity
 Nonspecific defense system
 Broad reactivity uniform in all members of a species
 Pathogens can be detected and destroyed within minutes or
hours
 Do not rely on expansion of antigen-specific lymphocytes.
 The innate immune system uses a limited number of secreted
proteins and cell-associated receptors to detect infection.
• These are called innate receptors because they are inborn

10. Properties & functions of innate immune
response
• The innate immune system maintains physical and
chemical defenses at epithelial barriers such as
the skin and lining of the gastrointestinal and
respiratory tracts, which block microbial entry.
• Innate immune responses are the initial reactions
to microbes that serve to prevent, control, or
eliminate infection of the host by many pathogens.
• Innate immunity eliminates damaged cells and
initiates the process of tissue repair.

11. Properties & functions of innate immune
response….
• Innate immune responses stimulate adaptive immune
responses and can influence the nature of the adaptive
responses to make them optimally effective against
different types of microbes.
• The two major types of protective reactions of the innate
immune system are
i. Inflammation
By recruiting phagocytes and other leukocytes that destroy the
microbes
ii. Antiviral defence.
By blocking viral replication or killing virus-infected cells without
a need for an inflammatory reaction

12. Components of Innate Immunity
• Comprise four types of defensive barriers:
1. Physical/Anatomic barriers
2. Physiologic barriers
1. Phagocytic barriers
2. Inflammatory barriers

13. Components…
• Anatomical and physical barriers
 Mechanical factors
 Chemical factors
 Biological factors
• Humoral components
 Complement
 Coagulation system
 Cytokines
• Cellular components
 Neutrophils
 Monocytes and macrophages
 NK cells
 Eosinophils

14. 1. Physical and anatomic Barriers
1. Skin
Two layers: epidermis and dermis.
• The epidermis contains several layers of tightly packed
epithelial cells and dead cells filled with a waterproofing
protein called keratin.
• Dermis composed of connective tissue, contains blood
vessels, hair follicles, sebaceous glands, and sweat
glands..

15. 1. Physical and anatomic Barriers
2. Mucosal Surfaces/membrane
• lining of Conjunctivae, alimentary, respiratory, and
urogenital tracts.
• Prevent entry by inhibiting binding of pathogens to the
epithelial cells via actions of:
 Saliva, tears and mucosal secretion
 Secreted juice
 Viscus fluid (mucus) secreted by epithelial cells.

16. 1. Physical and anatomic Barriers…
3. Normal flora
• Nonpathogenic organisms colonizing epithelial cells of
mucosal surfaces.
• Outcompete pathogens for attachment sites on the
epithelial cell surface and for necessary nutrients.
• Bactericide production

18. Components of Innate Immunity
• Comprise four types of defensive barriers:
1. Physical/Anatomic barriers
2. Physiologic barriers
3. Phagocytic barriers
4. Inflammatory barriers

19. 2. Physiologic barriers
1 Temperature
• Normal body temperature inhibits growth of some
pathogens
• Fever also inhibit growth of some microbes
2. Low pH
• Gastric acidity allow very few microorganisms to survive

20. 2. Physiologic barriers…
(Molecules/humoral components)
3. Lysozyme
• Cleaves the peptidoglycan layer of the bacterial cell wall
4. Surfactant proteins (collectins)
• Kill certain bacteria directly either by disrupting their lipid
membranes or aggregating the bacteria to enhance their
susceptibility to phagocytosis

21. 2. Physiologic barriers
5. Interferon
• Group of proteins produced by virus infected cells to bind
to nearby cells and induce a generalized antiviral state.
6. Complement
• A group of serum proteins that circulate in an inactive state
• Activated complement has ability of either destroying the
pathogens or facilitate their clearance.

22. Phisical & Physiological barriers

24. Components of Innate Immunity
• Comprise four types of defensive barriers:
1. Physical/Anatomic barriers
2. Physiologic barriers
3. Inflammatory barriers
4. Phagocytic barriers

25. 2. Inflammatory Response
Characterized by release of cytokines from macrophages
and other inflammatory mediators.
• Response occurs rapidly and limit spread of pathogen
until adaptive response is initiated.
• Triggered by injury – trauma, heat, chemical irritation,
infection, etc.

26. Inflammatory mediators
1. Macrophages release cytokines like IL-1, TNF-α, and
derivatives of arachidonic acid
2. Acute-phase proteins-chemical mediators released
increases in response to tissue damage;
 C-reactive protein is a major acute-phase protein
produced by the liver in response to tissue damage
 Binds to the C-polysaccharide cell-wall component
found on a variety of bacteria and fungi activates
the complement system

27. Inflammatory mediators..
3. Histamine
• Released by a variety of cells in response to tissue injury
• Binds to receptors on nearby capillaries and venules,
causing vasodilation and increased permeability
The cardinal signs of inflammation are Redness Heat,
Swelling and Pain

28. Events of an inflammatory response
1. Vasodilation;
• The vessels that carry blood away from the affected area
constrict, resulting in engorgement of the capillary
network
• Resulting in tissue redness (erythema) and an increase
in tissue temperature

29. Events of an inflammatory response…
2. An increase in capillary permeability
• Facilitates an influx of fluid and cells from the engorged
capillaries into the tissue.
• Accumulation of exudates contributes to tissue swelling
(edema)
3. Influx of phagocytes into the tissues
• Release lytic enzymes, which can damage nearby
healthy cells
• Accumulation of dead cells, digested material, and fluid
forms pus.

31. Components of Innate Immunity
• Comprise four types of defensive barriers:
1. Physical/Anatomic barriers
2. Physiologic barriers
3. Inflammatory barriers
4. Phagocytic barriers

32. C. Cellular innate immunity
• The common myeloid progenitor (CMP) is the precursor
of the macrophages, granulocytes (i.e. neutrophils,
eosinophils, and basophils), mast cells, and dendritic
cells of the innate immune system.
• Macrophages, granulocytes, and dendritic cells make up
the three types of phagocytes in the immune system.

33. Innate Immune Cells
 Phagocytes
• Specialized phagocytic cells, primarily macrophages
and neutrophils, are the first line of defense against
microbes that breach epithelial barriers.
• Some macrophages are always present in most
tissues and function as sentinels of infection, while
other phagocytes, including monocytes and
neutrophils, are recruited into infected tissues in
response to microbes or signals generated by the
sentinel cells.

34. Innate Immune Cells
 Dendritic Cells
• DCs detect invading microbes because of their
location in tissues and their expression of numerous
pattern recognition receptors for PAMPs and DAMPs.
• They secrete inflammatory cytokines that promote
recruitment of additional leukocytes from the blood.

35. Dendritic Cells….
• The plasmacytoid subset of DCs is a major source of the
antiviral cytokines, type I interferons, produced in
response to viral infections.
• The reactions of DCs to microbes in the early innate
response enhance the ability of the DCs to activate T
cells in the subsequent adaptive immune response

36. Innate Immune Cells
 Cytokine-Producing Innate Lymphoid Cells (ILCs)
ILCs are bone marrow–derived cells with lymphocyte
morphology that were discovered as cells that
produced cytokines similar to those made by T cells
but lacked TCRs.
There are different subsets of ILCs that arise from the
same common lymphoid precursor that gives rise to B
and T cells, but the precise steps in ILC development
are not fully understood, especially in humans.

37. Cytokine-Producing Innate Lymphoid Cells…
• Three subsets of innate lymphoid cells, called ILC1,
ILC2, and ILC3, produce different cytokines and express
different transcription factors.
• The cytokines each subset produces determine the roles
of these cells in defense.

39. Cytokine-Producing Innate Lymphoid Cells…
– NK cells, often considered the first known ILC, are
cytotoxic cells that play important roles in innate
immune responses, mainly against viruses and
intracellular bacteria.
– NK cells also secrete IFN-γ and are sometimes
referred to as a type of ILC1.
– NK cells have granules that contain proteins that
mediate killing of target cells. When NK cells are
activated, granule exocytosis releases these proteins
adjacent to the target cells. E.g perforin, granzymes

41. Innate Immune Cells
 Mast Cells
– Contain abundant cytoplasmic granules filled with
various inflammatory mediators that are released
when the cells are activated.
– The granule contents include vasoactive amines (e.g
histamine) that cause vasodilation and increased
capillary permeability, and proteolytic enzymes
– Mast cells also synthesize and secrete lipid mediators
(e.g prostaglandins) and cytokines (e.g TNF).

42. Recognition Of Microbes And Damaged Self By
The Innate Immune System
 The innate immune system recognizes molecular
structures that are produced by microbial pathogens.
• The microbial substances that stimulate innate
immunity are often shared by classes of microbes and
are called pathogen-associated molecular patterns
(PAMPs).
• The innate immune system recognizes microbial
products that are often essential for survival of the
microbes.

43. Pathogen associated molecular patterns
(PAMPs)
• Unique microbial molecules recognized by the immune
system.
• Highly conserved, general, only to microorganism. e.g,
virus; Capsid, spike, viral envelope,
genome
Bacteria; cell wall (LPS), flagella, cilia bacteria
genome
• Different types of microbes (e.g., viruses, gram-negative
bacteria, gram-positive bacteria, fungi) express different
PAMPs as shown below

44. Recognition Of Microbes And Damaged Self By
The Innate Immune System..

45. Damage associated and molecular patterns
(DAMPs)
 The IIM also recognizes endogenous molecules that
are produced by or released from damaged and dying
cells.
– DAMPs, as a result of cell damage caused by
infections, but they may also indicate sterile injury due
to chemical toxins, burns, trauma, or loss of blood
supply.
– In some cases, endogenous molecules that are
produced by healthy cells are released when the cells
are damaged, and they then stimulate innate
responses.

46. Recognition Of Microbes And Damaged Self By
The Innate Immune System…

47. Recognition Of Microbes And Damaged Self By
The Innate Immune System
• The innate immune system uses several types of cellular
receptors, present in different locations in cells, and
soluble molecules in the blood and mucosal secretions,
to recognize PAMPs and DAMPs.
• Cell-associated recognition molecules of are expressed
by phagocytes, dendritic cells, epithelial cells that form
the barrier interface between the body and the external
environment, mast cells, and many other types of cells
that reside in tissues.

48. Pattern recognition receptors (PRRs)
• The cellular receptors for pathogen- and damage associated
molecular patterns are called pattern recognition receptors..
• Receptor expressed on the plasma membrane of cell of
innate immunity
• Macrophages, neutrophils, dendritic cells
• Also present in cellular compartments
• Endosomes, lysosomes, cytosol
• Thus unable to detect both intercellular and extracellular
stress

50. Pattern recognition receptors (PRRs)
• 3 Types of PRR
• Membrane bound (TLRs, CLRs)
• Cytoplasmic sensor (NLRs, RLRs)
• Inflammasomes
• Each PRR can detect multiple pathogenic species which
share same PAMPs.
• PRRS
• TLRs – toll like receptors
• CLRs – c-type lectin receptors
• RLRs – RIG-like receptors
• NLRs – NOD-like receptors

52. PAMPs and DAMPs

53. Oxygen-dependent Killing Mechanisms
• Activated phagocytes produce a number of reactive oxygen
intermediates (ROIs) and reactive nitrogen intermediates
that have potent antimicrobial activity.
• During phagocytosis, a metabolic process known as the
respiratory burst occurs in activated macrophages.
• This process results in the activation of a membrane-bound
oxidase that catalyzes the reduction of oxygen to superoxide
anion, a reactive oxygen intermediate that is extremely toxic
to ingested microorganisms.
53

54. Oxygen-dependent Killing Mechanisms
• The superoxide anion also generates other powerful
oxidizing agents, including hydroxyl radicals and
hydrogen peroxide.
• As the lysosome fuses with the phagosome, the activity
of myeloperoxidase produces hypochlorite from
hydrogen peroxide and chloride ions.
• Hypochlorite (bleach) is toxic to ingested microbes.
54

56. Nitric Oxide Dependent Killing
Mechanisims
• When macrophages are activated with bacterial cell-wall
components such as lipopolysaccharide (LPS) or, muramyl
dipeptide (mycobacteria), and a T-cell–derived cytokine
(IFN-ϒ),
• Express high levels of nitric oxide synthetase (NOS), an
enzyme that oxidizes L-arginine to yield L-citrulline and
nitric oxide (NO) gas:
• L-arginine + O2+ NADPH →NO + L-citrulline + NADP

57. Nitric Oxide Dependent Killing
mechanisims
• Nitric oxide has potent antimicrobial activity; it also can
combine with the superoxide anion to yield even more
potent antimicrobial substances.
• Much of the antimicrobial activity of macrophages
against bacteria, fungi, parasitic worms, and protozoa is
due to nitric oxide and substances derived from it.
57

58. Oxygen-independent Killing Mechanisms
Activated macrophages also secrete;
• Lysozyme
Which contains various hydrolytic enzymes which degrades
antigen without oxygen requirement.
• Defensins
– group of antimicrobial and cytotoxic peptides, form ion-
permeable channels in bacterial cell membranes to kill a
variety of bacteria, including Staphylococcus aureus,
Streptococcus pneumoniae, Escherichia coli,
Pseudomonas aeruginosa, and Haemophilus influenzae.
• Tumor necrosis factor (TNF-α), a cytokine that
has a variety of effects and is cytotoxic for some
tumor cells.
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59. Adaptive immunity

61. Adaptive Immunity
• Unlike innate immunity, it is stimulated by exposure to
infectious agents and increase defensive capabilities
with each successive exposure to a particular microbe.
• Develops as a response to infection and adapts to the
infection, so it is called adaptive immunity
(specific/acquired immunity).
• The adaptive immune system recognizes and reacts to a
large number of microbial and nonmicrobial substances,
called antigens.

62. Adaptive immunity..
• It is capable of recognizing and selectively eliminating
specific foreign microorganisms and molecules (i.e,
foreign antigens).
• Can be antibody mediated (humoral), cell mediated
(cellular), or both.
• The Adaptive Immune System Requires Cooperation
Between Lymphocytes and Antigen-Presenting Cells
(APC)

63. Cells of adaptive immunity
1. Lymphocytes
• WBCs which leave the bone marrow, circulate in the
blood and lymphatic systems, reside in various lymphoid
organs.
• Express antigen binding cell-surface receptors and hence
their specificity, diversity, memory, and self/nonself
recognition.
• The two major types:
 B cells and T cells

64. Cells of adaptive immunity….
2. Antigen-presenting Cells
• Immune cells that mediate the cellular immune response
by processing and presenting antigens for recognition by
certain lymphocytes such as T cells
• Classical APCs include dendritic cells, macrophages,
Langerhans cells.
• They all express class II MHC molecules on their
membranes

65. Features of Adaptive immunity
• Display four main charactoristics
i. Antigenic specificity
ii. Diversity
iii. Immunologic memory
iv. Self/nonself recognition

66. Features of Adaptive immunity
 Antigenic diversity.
• It is estimated that the immune system of an individual can
discriminate 107 to 109 distinct antigenic determinants.
• This ability of the lymphocyte repertoire to recognize a very
large number of antigens, called diversity, is the result of
variability in the structures of the antigen binding sites of
lymphocyte receptors for antigens.

67. Features of Adaptive immunity
 Antigenic specificity
• As an antigen binds to a particular T or B cell and
stimulates it to divide repeatedly into a clone of cells
with the same antigenic specificity as the original
parent cell (clonal selection)
• Only lymphocytes whose receptors are specific for a
given epitope on an antigen will be clonally expanded
and thus mobilized for an immune response

68. Features of Adaptive immunity
 Immunologic memory :
A consequence of clonal selection. During clonal selection,
the number of lymphocytes specific for a given antigen is
greatly amplified.
 Amplified population of memory cells accounts for the rapidity and
intensity secondary immune response
 Moreover memory cells have a longer life span than the naïve from
which they are derived
• Two reasons for stronger secondary immune response
1. Memory cells accumulate and become more numerous than the
naïve lymphocytes.
2. Memory cells react more rapidly and vigorously to antigen
challenge than do naive lymphocytes

69. Adaptive immune response
 Self/nonself discrimination;
• One of the most remarkable properties of every
normal individual’s immune system is its ability to
recognize, respond to, and eliminate many foreign
(nonself) antigens while not reacting harmfully to that
individual’s own (self) antigens.
• Immunologic unresponsiveness is also called
tolerance. Tolerance to self antigens, or self-
tolerance, is maintained by several mechanisms.

70. Humoral immune response
It is an antibody mediated immunity
• Involve interaction of B cells with antigen and their
subsequent proliferation and differentiation into antibody-
secreting plasma cells.
• Antibodies are glycoproteins consist of two identical
heavy polypeptide chains and two identical light
polypeptide chains

71. B lymphocytes
• B lymphocytes arise and mature
within the bone marrow
• Expresses a unique antigen-binding
receptor on its membrane, a
membrane-bound antibody
molecule.
• B cells have about 105 molecules of
membrane-bound antibody per cell.
 All the antibody molecules have
the same antigenic specificity can
interact directly with antigen.
71

72. B cell …
• When a naive B cell first encounters the antigen, the
antigen bind to the antibody
• Causes rapidly cell differentiation to memory B cells and
effector B cells called plasma cells.
• Memory B cells have a longer life span than naive cells,
and they express the same membrane-bound antibody
as their parent B cell.

73. B cell …
• Secreted antibodies are the major effector molecules of
humoral immunity.
• They bind to antigen and neutralizing it or facilitating its
elimination by:
 Phagocytosis
 Activation of the Complement system which lyse
foreign organism.
 Neutralization of toxins or viral particles by coating
with antibody which prevents binding to host cells.

74. Cell mediated immunity
• Effector T cells generated in response to antigen are
responsible for cell-mediated immunity
• Both activated TH cells and cytotoxic T lymphocytes
(CTLs) serve as effector cells in cell-mediated immune
reactions.
• Cytokines secreted by TH cells can activate various
phagocytic cells, enabling them to phagocytose and kill
microorganisms more effectively.

75. Cell mediated immunity
• Cell-mediated immune response is especially important
in ridding bacteria and protozoa contained by infected
host cells.
• CTLs participate in cell-mediated immune reactions by
killing altered self-cells
• play an important role in the killing of virus infected
cells and tumor cells.

76. Types of T lymphocytes
• There are two types of T cells:
– T helper (TH) and T cytotoxic (TC) cells distinguished
from one another by the presence of either CD4 (TH
cells ) or CD8 ( TC cells) membrane glycoproteins on
their surfaces
• Postulated third type a T suppressor (TS) cell,
– recent evidence suggests that it may not be distinct
from TH and TC subpopulations.

77. T cells…..
• CD4+ T cells recognize only antigen bound to class II
MHC molecules.
• CD8+ T cells recognize only antigen associated with
class I MHC molecules.
 In general, CD4+ cells act as helper cells and CD8+
cells act as cytotoxic cells.
• Both types of T cells express about 105 identical
molecules of the antigen binding T-cell receptor (TCR)
per cell
 all with the same antigenic specificity.

78. T cell role
• When a naive T cell encounters antigen combined with a
MHC molecule on a cell, the T cell proliferates and
differentiates into memory T cells and various effector T
cells.
• TH cell recognizes and interacts with an antigen to form
an antigen -MHC class II molecule complex and activate
it to an effector T cell
– Effector cell secretes various growth factors known
collectively as cytokines.

79. T cell role ….
• The secreted cytokines activate B cells, TC cells,
macrophages, and various other cells that participate in
different types of immune response.
• Under the influence of TH-derived cytokines, a TC cell
that recognizes an antigen–MHC class I molecule
complex proliferates and differentiates into an effector
cell called a cytotoxic T lymphocyte (CTL).

80. T cell role ….
• The CTL generally do not secrete many cytokines and
instead exhibits cell-killing or cytotoxic activity.
• The CTL monitors the cells of the body and eliminates
any that display antigen, such as virus-infected cells,
tumor cells, and cells of a foreign tissue graft.
• Cells that display foreign antigen complexed with a class
I MHC molecule are called altered self-cells; these are
targets of CTLs.

82. MHC
Major Histocompatibility Complex molecules;
 Antigen-recognition molecules that do not possess the
fine specificity for antigen characteristic of antibodies and
T-cell receptors.
• Each bind to a spectrum of antigenic peptides
Two major classes of membrane-bound glycoproteins:
 Class I MHC molecules are expressed on nearly all
nucleated cells.
 Class II MHC molecules are expressed only on antigen
presenting cells e.g. Monocytes, Macrophages, dendritic
cells, B cells
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83. Antigen recognition by Lymphocytes
• Antigens which are generally very large and complex, are
not recognized in their entirety by lymphocytes.
• Both B and T lymphocytes recognize immunologically active
regions on a complex antigen called antigenic determinants,
or epitopes.
• Where as B cells can recognize an epitope alone; T cells
can recognize an epitope only when it is associated with an
MHC molecule
83

84. Recognition molecules in immune
response
• Distinct cell-membrane molecules are responsible
for antigen recognition by the immune system:
 Membrane-bound antibodies on B cells
 T-cell receptors
 Class I MHC molecules
 Class II MHC molecules
• Each of these molecules plays a unique role in antigen
recognition, ensuring that the immune system can
recognize and respond to the different types of antigen
that it encounters.
84

85. Anti-Viral Immunity
Anti-viral activity of interferons (IFNs)
• Virus infected cells produce INF-α;
• INF-α inhibit intracellular replication of viruses
• IFN-α activate NK-cells to kill virus infected cells
• IFNs have no direct effect on extracellular virus
• IFNs act early in viral diseases before antibody
• INFs activity is not specific

86. Interferons Are Antiviral Proteins Produced by Cells in
Response to Viral Infection

87. Anti-Viral Immunity
Humoral immunity:
• Virus neutralization
– In viremic infections, Antibodies neutralize virus,
preventing its attachment to receptor sites on
susceptible cells
e.g. Poliovirus, mumps, measles, rubella
– In superficial non-viremic infections (influenza)
Secretory IgA neutralizes virus infectivity at the
mucous surfaces

88. Anti-Viral Immunity
• Antibodies destroy free virus particles directly by:
 Aggregation of virus and opsonization
 Complement mediated lysis
• Both mechanisms also act on virus infected cells

89. Anti-Viral Immunity
Cell mediated immunity:
• Cell mediated cytotoxicity, mediated by ;
– Cytotoxic T-cells (CTLs)
– NK cells
– Activated macrophages
• CMI acts on virus infected cells through:
– CTLs kill virus infected cells directly after recognition
of viral antigens on cell surface in association with
MHC I

90. Anti-Viral Immunity
– TH-cells stimulated by viral antigens release
cytokines which attract and activate macrophages to
kill virus infected cells
– Nk-cells destroy virus infected cells early in infection
before appearance of antibodies
– Antibody-dependent cell mediated cytotoxicity
(ADCC): Antibody binds to virus infected cells such
cells are lysed by NK cells, macrophages and
polymorphs

91. Anti-Fungal Immunity
Immune response to fungi consist mainly of :
1) Innate immunity is mediated by:
- Neutrophils and macrophages
- Fungi are readily eliminated by phagocytes
2) Acquired immunity (cell mediated immunity)
- CMI acts in a manner similar to its action against
intracellular bacteria
* Disseminated infection are seen in: immunodeficiency

92. Comparison of immunity
• Innate immune response is rapid which utilizes a pre-
existing but limited repertoire of responding components.
• Adaptive immunity has slower onset, and have ability to
recognize a much wider repertoire of foreign substances,
and ability to improve during a response, whereas innate
immunity remains constant.
92

93. Comparison of immunity
• Secondary adaptive
responses are
considerably faster than
primary responses.
• With overlapping roles,
the two systems together
form a highly effective
barrier to infection.
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94. Relationship between innate and adaptive
immunity
• Two systems work together to eliminate a foreign invader
through the carefully regulated interplay
 The phagocytic cells crucial to nonspecific immune
• Responses are intimately involved in activating the specific
immune response.
• Conversely, various soluble factors produced by a specific
immune response augment the activity of these phagocytic
cells.

95. Relationship…
• Interactions between receptors on macrophages and
microbial components generate soluble proteins that
stimulate and direct adaptive immune responses.
 Also secretes cytokines that can direct adaptive
immune responses
• Adaptive immune system produces signals and
components that stimulate and increase the
effectiveness of innate responses
• Some T cells, when they encounter appropriately
presented antigen, synthesize and secrete cytokines that
increase the ability of macrophages to kill the microbes
they have ingested.

96. Relationship….
• Antibodies produced against an invader bind to the
pathogen, marking it as a target for attack by
complement and serving as a potent activator of the
attack.
• inflammatory response produce soluble mediators that
attract cells of the immune system

97. Refferences
1. Kuby Immunology, 6th edition, 2007.
2. Jawetz, Melnick, & Adelberg’s Medical Microbiology 26th Edition
3. Really Essential Medical Immunology 2nd edition
4. Textbook of microbiology by Surinder Kumar