For MBBS students

1. Immune Response
Dr. Pendru Raghunath Reddy
Assistant Professor
Dept of Microbiology
Dr. VRK Women‟s Medical College

2. Definition
The specific reactivity induced in a host following an
antigenic stimulus

4. Consequences of Immune response
1. Beneficial to the host
2. Indifferent
3. Injurious to the host
The state of specific nonreactivity (tolerance) induced by certain
types of antigenic stimuli also included in it

5. Types of Immune response
The immune response can be divided into two types
1. The humoral (antibody mediated) immunity
2. Cell-mediated immunity (CMI)
 These two are usually developed together, though at times
one or other may be predominant or exclusive
 They usually act in conjunction but sometimes they may act in
opposition

6. Role of humoral immunity
1. Provides primary defense against most extracellular bacterial
pathogens
2. Helps in defense against viruses that infect through the
respiratory or intestinal tracts
3. Prevents recurrence of virus infections
4. Participates in the pathogenesis of immediate (type 1, 2, and 3)
hypersensitivity and certain autoimmune diseases

7. Role of cell – mediated immunity (CMI)
1. Protect against fungi, viruses and facultative intracellular
bacterial pathogens like Mycobacterium tuberculosis,
M. leparae, Brucella and Salmonella and parasites like
Leishmania and trypanosomes
2. It provides immunological surveillance and immunity against
cancer
3. Participates in the rejection of homografts and garft-versus-host
reaction
4. Mediates the pathogenesis of delayed (type IV) hypersensitivity
and certain autoimmune diseases

8. Humoral immunity
Synthesis of antibody
Antibody production follows a characteristic pattern
1. Lag phase
2. Log phase
3. A Plateau or Steady phase
4. The phase of decline

9. Primary and secondary responses
The kinetics and other characteristics of the humoral response
differ considerably depending on whether the humoral response
results from activation of naïve lymphocytes (primary response)
or memory lymphocytes (secondary response)

10. Primary humoral response
 Characterised by a long lag phase and low titre of antibodies
that do not persist for long
 The antibody formed is predominantly IgM
 A single injection of an antigen helps more
in priming the immunocompetent cells
to produce the particular antibody
rather than in actual elaboration of high
levels of antibody

11. Secondary humoral response

12. Fate of antigens in tissues
The manner in which an antigen is dealt within the body
depends on many factors
1. Physical and chemical nature of the antigen
2. Dose and route of entry
3. Speed of elimination
4. Primary or secondary antigenic stimulus

13. Production of antibodies
 The majority of antigens will stimulate B cells only if they have
the assistance of TH cells
 Antigens can be divided into two categories based on their
apparent need for TH cells for the induction of antibody
synthesis
1. T – dependent antigens (TD – antigens)
eg: Proteins and erythrocytes
2. T – independent antigens (TI – antigens)
eg: Polysaccharides and other structurally simple molecules
with repeating epitopes

15. Antigen processing and presentation

16. T cell activation

17. T cell - mediated B cell activation

18. Polyclonal antibodies
Synthesised by several different clones of B cells against different
epitopes of the same antigen
Monoclonal antibodies
Produced by a single clone of B cells and directed againat a single
antigenic determinant (epitope)

19. Hybridoma technology

20. Principle
• MYELOMA CELLS HAVE
LOST the ability to
synthesize hypoxanthine-
guanine-phosphoribosyl
transferase (HGPRT), an
enzyme necessary for the
salvage synthesis of
nucleic acids
• Which enables cells to
synthesize purines by the
salvage pathway here using
an extracellular source of
hypoxanthine as a precursor

21. • The selective culture medium is
called HAT medium because it
contains Hypoxanthine,
Aminopterin, and Thymidine
• Unfused myeloma cells cannot
grow because they lack
HGPRT
• Unfused normal spleen cells
cannot grow indefinitely
because of their limited life
span.

23. Problems with using mouse monoclonal
antibodies
• The therapeutic use of rodent monoclonal antibodies in
humans is limited by their immunogenic, short circulating
half-life, and inability to efficiently trigger human effectors
mechanisms
• This is due to differences between the mouse and humans.
• Also severe allergic response in human when mouse mAb
are introduced to a patients.
• Also constant region of murine mAb are not effective in
interacting with human effectors molecules.

24. Chimeric monoclonal antibodies
• Monoclonal antibodies are genetically engineered using a
molecular approach
• Chimeric Abs are obtained by genetically fusing the mouse
variable domains to human constant domains
• Variable regions are isolated using polymerase chain
reaction (PCR)

25. Humanized monoclonal antibodies
 The complementarity determining regions (CDRs), which are
the responsible for antigen binding within the variable
regions, have been transferred to human frameworks
creating „„CDR-grafted‟‟ or „„humanized‟‟ antibodies

26. Uses of monoclonal antibodies
1. Diagnostic use
Many commercial diagnostic systems use monoclonal
antibodies for identification of bacterial, viral and other antigens
2. Used in cancer therapy
3. Used in the identification of tumor and other surface antigens
4. Used in identification of functional populations of different
types of T cells
5. Purification of desired proteins

27. Factors influencing antibody production
1. Age
2. Genetic factors
3. Nutritional status
4. Dose of antigen
5. Route of administration
6. Multiple antigens
7. Adjuvants
8. Immunosupressive agents

28. Age
 The embryo is immunologically immature
 Production of antibodies starts after the development and
differentiation of lymphoid organs
 Immunocompetence is not complete at birth
 Full competence is acquired only by the age of 5 – 7 years for
IgG and 10 – 15 years for IgA

29. Genetic factors
 The immune response is under genetic control
 The immune response in different individuals to same antigen
varies due to genetic factors
 Persons capable of responding to a particular antigen are called
“responder” and those who do not respond are termed
“nonresponder”

30. Multiple antigens
When two or more antigens are administered simultaneously,
the effects may vary
1. No effect
(eg: Mixture of typhoid and cholera vaccines)
2. Synergistic effect
(eg: DPT vaccine)
3. Antagonistic effect
(eg: Mixture of diphtheria and tetanus toxoids with one in
excess)

31. Adjuvants
 Any substance that enhances the immunogenicity of an antigen
is called adjuvant
 Adjuvants are often used in research and clinical settings to
boost the immune response when an antigen has low
immunogenicity or when only small amounts of an antigen
are available

32. Precisely how adjuvants augment the immuneresponse is not
entirely clear
Action of adjuvants
1. Sustained release of antigen (Depot)
2. Enhance costimulatory signals
3. Stimulate lymphocytes non-specifically
4. Activate macrophages and stimulate CMI
5. Increase local inflammation

33. Types of adjuvants
1. Depot
 Aluminium hydoxide or phosphate, aluminium potassium
sulfate (alum) and Freund‟s incomplete adjuvant
(water in oil suspension)
 When an antigen is mixed with alum, the salt precipitates the
antigen. Injection of this alum precipitate results in slower
release of antigen from the injection site
 Freund‟s incomplete adjuvant contains antigen in aqueous
solution, mineral oil and emulsifying agent such as
manninde monooleate, which disperses the oil into small
droplets surrounding the antigen

34. 2. Bacterial
Examples: Freund‟s complete adjuvant and
bacterial lipopolysaccharides
 Freund‟s complete adjuvant: Freund‟s incomplete adjuvant +
heat-killed Mycobacteria
 Muramyl dipeptide, a component of the mycobacterial cell wall
activates dendritic cells and macrophages
3. Chemical
Bentonite, calcium alginate and silica particles

35. Immunosupressive agents
1. X-irradiation
2. Radiomimetic drugs
3. Corticosteroids
4. Atimetabolites
5. Antilymphocytic serum (ALS)
6. Cyclosporine

36. Cell-Mediated Immunity
• It is a specific acquired immune response
mediated by specific cells of the immune system
– Primarily T lymphocytes (T cells), but also macrophages, NK
cells and K cells
– This type of immunity can be transferred from one organism
to another by intact lymphoid cells, but not by antisera
• T cells are the main agents of cellular immunity

37. – Involves specialized set of lymphocytes called T cells
that recognize foreign antigens on the surface of cells,
organisms, or tissues:
• Helper T cells
• Cytotoxic T cells
– T cells regulate proliferation and activity of other cells
of the immune system: B cells, macrophages,
neutrophils, etc.
– Defense against:
• Bacteria and viruses that are inside host cells and
are inaccessible to antibodies.
• Fungi, protozoa, and helminthes
• Cancer cells
• Transplanted tissue

38. CD4+ T helper Subsets
• CD4+ Thelper cells can be divided into subsets based on
their cytokine production.
• Th1 cells produce IL-2, IFN-γ, TNF-β cytokines which
activate cell mediated immunity
• Th2 cells produce IL-4, IL-6, IL-10 that activate
humoral immunity
• These subsets were originally identified using mouse
T- cell clones.

39. Fig. 13-7

40. T-cell Activation
Signal 1
TCR
MHC II
Mature
Dendritic Activated
TH
cell Tcell
H cell
APC B7 CD28
Signal 2

42. Induction of CMI

45. Cytotoxic T cells
• CTLs recognize cells that have been infected
– Virus
– Transformed to tumor
• CTL activation is divided into 2 phases
– Activation and differentiation of naïve CTL
– Effector recognizes Class I MHC/peptide and destroys
target

46.  Naïve CTLs cannot Kill; referred to as CTL-Ps (precursors)
 3 signals needed for activation
1. Ag specific signal through TCR/MHC I+Ag
2. Co-stimulatory signal CD28(CTL)/B7 (APC)
3. IL-2 signaling inducing proliferation
IL-2 is provided by TH1 or CTL-P itself
IL-2R is expressed only after activation

47. How CTLs kill
• 4 Phases In CTL Killing
– Conjugate formation
• LFA-1 (CTL) binds ICAMs (Target)
– LFA-1 changes to high avidity if Ag Is Recognized
– Activated LFA-1 persists for 5-10 mins
– Membrane attack
• Requires Ca2+ and energy
– Granules release Perforins (65 kDa) and Granzymes (serine proteases) at the
junctional space
– Perforins polymerize forming cylindrical pores (5-20 nm), Ca2+ is needed
– Granzymes enter target cell
– Granzyme B can enter thru mannose-6-phosphate receptor in a vesicle
– DNA fragmentation
– CTL dissociation
– Target cell destruction
• Apoptotic death within a few hours

48. CTL-Killing

49. One cytotoxic T cell can kill multiple
targets
• A cytotoxic T cell causes its target to undergo apoptosis (cell suicide)
by the focussed secretion of vesicles carrying cytotoxins.
• The T cell binds to its target, delivers its cytotoxins, and moves on
before it has a chance to be hurt itself (one T cell can kill another, so
a T cell is not immune to the cytotoxins).

50. Cytokines
These are biologically active substances secreted by
lymphocytes, leucocytes, monocytes and other cells
• Interleukins - Cytokines secreted by leukocytes that have
the ability to act as signal molecules between different
population of leukocytesIL-1~IL-29
• Lymphokines - produced by lymphocytes
• Monokines - produced exclusively by monocytes
• Interferons - involved in antiviral responses
• Colony Stimulating Factors - support the growth of cells in
semisolid medias
• Chemokines - promote chemotaxis.

51. Characteristics of cytokines
1. Cytokines are peptide mediators or intracellular messengers which
regulate immunological, inflammatory and reparative host responses
2. They are highly potent hormone-like substances, active
even at femtomolar (10-15 M) concentrations
3. They differ from endocrine hormones in being produced not by
specialised glands but by widely distributed cells
4. Cytokines can affect the same cell responsible for their production
(an autocrine function), near by cells (a paracrine function) or can be
distributed by the circulatory system to their target cells (an endocrine
function)
5. Their production is influenced by nonspecific stimuli. Some cytokines
also can induce the production

52. One kind of cytokines can be produced by different
cells. One kind of cells can secrete different cytokines
IL-2 IL-4，6
TH1 IL-3,GM-CSF,TNF- TH2
IFN-γ,TNF-β IL-5

53. Cytokines initiate their actions by binding to specific
membrane receptors on target cells

54. self
autocrine
Cytokines take effect
in three ways
paracrine Nearby
Blood circulation
endocrine Distance

55. Properties of cytokines
The effects of cytokines are often pleiotropism, redundant,
synergy, antagonism, and form a cytokine network
• Pleiotropism refers to the ability of one cytokine having
multiple effects on diverse cell types.

56. • Redundancy refers to the property of multiple
cytokines having the same or overlapping
functional effects

57. • Synergy refers to the property of two or more
cytokines having greater than additive effects.

58. • Antagonism refers to the ability of one cytokine
inhibiting the action of another

59. Interleukin-1
• Interleukin I divided into Alpha and Beta
• IL1 is secreted by Macrophages, Monocytes other
nucleated cells
• Stimulated by antigens, toxins, injury, inflammation
• Inhibited by cyclosporins,corticosteiods,prostaglandins

60. Functions of Interleukin-1
• IL1 stimulates T cells for the production of IL-2 and
other lymhokines
• Helps B cell proliferation
• Synthesizes antibodies
• Helps neutrophils in chemotaxis
• Promotes phagocytosis
• Promotes metabolic physiological and inflammatory
responses by action on bone marrow

61. IL-1 initiates Fever
• IL-1 is crucial in
promoting fever and
called as Pyrogen.
• With the help of
Tumor necrosis factor
causes hematological
changes in
Septicemias, Shock
and bacterial
meningitis
61

62. IL-2
• A T cell growth factor (TCGF) produced by activated T cells
• IL-2 important actions:
– It can increase immunoglobulin synthesis and J-chain
transcription
– Proliferation in B cells (with IL-4)
– potently augment the cytolytic activity of natural killer (NK) cells
– Stimulates cytotoxic T cells
– Converts certain null cells (LGL) into lymphokine-activated killer
(LAK) cells
– Due to its effects on T-cells and B-cells IL-2 is a central regulator
of immune response
– Passes Blood Brain Barrier

64. IL-4
• IL-4, like IL-2, is produced principally by
activated CD4+ T cells
• It is also produced by natural killer cells, and
by mast cells and basophils

65. IL-4 Actions
• IL-4 is the major B-cell growth factor (BCGF-1)
• Vital for immunoglobulin class switch IgG to IgE and
inhibits the synthesis of IgM and other IgG subtypes
• IL-4 induces expression of class II major histocompatibility
complex (MHC) molecules on B cells
• Enhances the activity of cytotoxic T cells
• IL-4 can inhibit responses of cells to IL-2

66. Tumor necrosis factor (TNF)
TNFs were originally thought of as selective antitumour agents,
but are now known to have a multiplicity of actions
 Occurs as two types; TNF- and TNF-
 TNF- is produced mainly by LPS activated monocytes and
macrophages
 Resembles IL-1 in having a very wide spectrum of biological
activities (endotoxic shock)
 Has immunomodulatory influences on other cytokines
 TNF- (lymphotoxin, LT) is produced mainly by activated Th0
and Th1
 TNF- actions are similar to those of TNF-

68. Interferons
A group of glycoproteins that produced by human or
animal cells following the infection of virus and
exposure to various inducing agents

69. Comparison of IFN- , IFN- , IFN-
_____________________________________
Types Produced cells Main functions
____________________________________
IFN- leukocytes anti-virus,immune regulation
IFN- fibroblasts anti virus, anti-tumor
IFN- Th1,NK cells immunoregulatory functions
_____________________________________

71. Immunological Tolerance
 Defined as the absence of specific immune response resulting
from a previous exposure to the inducing antigen
 This nonreactivity is specific to the particular antigen, immune
reactivity to other antigens being unaffected
 Tolerance to self is initially induced during embryonic life
 Tolerance occurs in both T and B cells
 Multiple mechanisms of tolerance exist

72. Immune tolerance is of two types
1. Natural tolerance
2. Acquired tolerance
Natural tolerance
 Non-responsiveness to self antigens
 Any antigen that comes in contact with the immunological
system during its embryonic life would be recognised as self
antigen and would not provoke an immune response in the
mature animal

73. Burnet‟s clonal selection model:
DEVELOPMENT MATURITY
Clonal
Deletion
Anti-self Self Ag
Lymphocyte
Activation
Differentiation
Anti-non-self Foreign Ag + second signal
Lymphocyte

74. x
Medawar’s experiment demonstrating
neonatal tolerance induction (Nobel Prize)

75.  The induction of tolerance depends on the species and
immunocompetence of the host, physical nature, dose and
route of administration of antigen
 Tolerance to humoral and cellular immunity is usually induced
simultaneously
 When unresponsiveness is established for one branch of the
immune response, it is called “split tolerance”
 Tolerance can be overcome spontaneously or by an injection
of cross reacting immunogens