This is a series of lectures on microbiology useful for undergraduate medical and paramedical students

1. IMMUNITY
Concepts
(Immunity, antigens, antibodies, antigen
antibody reactions, vaccines)
Dr. Ashish V. Jawarkar
M.D.

2. INFECTION

3. Relationship between host and
infectious agent
 Saprophytes – live on dead tissue – do not
cause diseases
 Parasites – multiply in hosts
 Pathogens – cause diseases
 Commensals – donot cause diseases
normally – only during immunosuppression

5. Infection
 Lodging of parasite in tissues of host
 This is not necessarily disease

6. Disease
 Any deviation from good health

7. Infectious disease
 Any deviation from good health due to
infectious agent

8. Infection
 Primary infection – in healthy host
 Re-infection – repeat infection by the
same agent
 Secondary infection – second infection by
a new agent

10. Infection
 Acute – rapid progress
 typhoid
 Chronic – slow onset and progress
 tuberculosis

11. Infection
 Localised – restricted to specific area
 Systemic

12. Infection
 Clinical – with symptoms
 Subclinical – no obvious symptoms

13. Infection
 Oppurtunistic – when host resistance is
lowered
 Nosocomial – acquired from hospital, not
present on admission
 Laboratory acquired – from laboratory

14. Sources of infection
 Humans – carriers
 Animals – zoonoses
 Insects
 Soil and water
 Food

15. Methods of transmission
 Contact – direct, indirect, sexual
 Inhalation
 Ingestion
 Inoculation
 Insects
 Congenital – vertical
 Iatrogenic

16. Pathogenicity
 Capacity of micro organisms to cause
diseases

17. Virulence
 Degree of pathogenicity

18. Factors predisposing to
pathogenicity
 Adhesion – attachment due to receptors
and ligands

19. Factors predisposing to
pathogenicity
 Invasiveness
 Highly invasive – septicemia following wound
infection by streptococci
 Less invasive – staphylococcal abscess

20. Factors predisposing to
pathogenicity
 Toxins
 Exo toxins – released outside
 Endotoxins – LPS (part of cell wall)

21. Factors predisposing to
pathogenicity
 Communicability
 Ability to spread from one host to other
 Ensures survival

22. Types of infectious diseases
 Endemic – constantly present in a
particular area
 Eg typhoid
 Epidemic – one that spreads rapidly
involving many persons at the same time
 influenza
 Pandemic – spreads through many areas
of the world at the same time

23. IMMUNITY

24. Immunity
 Resistance exhibited by host towards
micro organisms

25. Types of immunity
 Innate
 Immunity that a person possesses due to
genetic make up
 Acquired
 Active
• Acquired after an exposure to infection (natural) /
artificially induced (vaccine)
 Passive
• Injection of antibodies

26. Innate immunity Epithelial surfaces
 Skin
 Mucosa
 Saliva
 Urine
 Antibacterial systems in blood and tissues
 Complement system
 Interferons
 Microbial antagonism
 Flora
 Cells
 macrophages
 Neutrophils
 NK cells
 Inflammation
 Fever
 Acute phase proteins
 CRP

27. Acquired (Active)
 Due to stimulation by an antigen (like
microorganism)
 Long lasting
 Associated with memory

28. Active immunity
 Natural active
 Clinical or subclinical infection
 Eg chicken pox
 Artificial active
 vaccines

29. Passive immunity
 Natural passive
 Placenta
 Breast milk
 Artificial passive
 Rh iso immunisation

30. HERD IMMUNITY
 Overall level of immunity in a community
 Useful in case of epidemics

31. OVERVIEW OF STRUCTURE AND
FUNCTION OF IMMUNE SYSTEM

34. Lymphocytes
 B lymphocytes – produce antibodies –
Humoral immunity
 T lymphocytes – cell mediated immunity

35. T cell maturation
(central lymphoid organs)

36. Central lymphoid organs
 Bone marrow
 Thymus

37. B cell maturation
(Peripheral lymphoid organs)

38. Peripheral lymphoid organs
 Lymph nodes
 Spleen
 Mucosa associated lymphoid tissue
(MALT)
 Tonsils
 Peyer’s patches

39. Other cells of the immune system
 ANTIGEN PRESENTING CELLS (APCs)

40. Phagocytes (macrophages)

41. Dendritic cells
eg Langerhan’s cell

42. MAJOR HISTOCOMPATIBILITY
COMPLEX (MHC)
 Differentiates between self and foreign

43. ANTIGENS AND ANTIBODIES

45. ANTIGEN
 Any substance which, when introduced
into the body stimulates production of
antibody

46. ANTIBODY
 Substance that is produced by the body
against the antigen is an antibody
 It is a protein
 Almost 25% of our body proteins are
Immunoglobulins

47. Types of antigens
 Xenoantigens – from different species
 Alloantigens – from same species
 Autoantigen – lens protein, testis
 Heterophile antigen – closely related
antigens from different species

48. Antigens – on the basis of ability to
cause disease
 Immunogen – develop undesired response
– transplants
 Tolerogens – induce immunological
tolerance due to memory
 Allergens – over reactions
 Vaccines – protective response

49. Biological classes of antigens
 T cell dependent
 T cell independent

50. Antibodies - types
 Ig G
 Ig A
 Ig M
 Ig D
 Ig E

51. Structure

52. IgG
 Can be transported across placenta,
provides immunity to new born
 Neutralize viruses
 Encourage phagocytosis

53. IgA
 Main immunoglobulin in mother’s milk,
saliva and tears
 Called secretory Ig
 Local immunity

54. IgM
 Earliest Ig to be synthesized by fetus
 Not transported across placenta
 Presence useful in diagnosis of congenital
infections such as syphilis, rubella, HIV
and toxoplasmosis
 Responsible for protection from blood
invasion by microorganisms

55. IgD
 Occur on the surface of B lymphocytes
(with IgM) and act as receptors for
antigens

56. IgE
 On mast cells and basophils
 Responsible for anaphylaxis
(hypersensitivity)

57. In short
 IgG - protects body fluids
 IgA – protects body surfaces
 IgM – protects the blood stream
 IgD – receptor on surface of B
lymphocytes
 IgE – mediates anaphylaxis

58. Antigen – Antibody reactions
 Antigen and antibody can react and cause
 Precipitation
 Agglutination
 Lysis
 Killing of live antigens (micro organisms)

59. Precipitation

60. Agglutination

61. Lysis

62. Killing of microorganisms

63. General features of antigen –
antibody reaction
 Reaction is specific
 Combination occurs at surface – so
surface antigens are relevant
 Combination is firm but reversible
 Antigen and antibody can combine in
variable proportions

64. Combinations occur at surface

65. Combination is reversible
 Affinity – intensity of attraction

66.  Avidity – strength of bond

67.  Combine in variable proportions

68. Applications
 Precipitation reactions
 Agglutination reactions
 Complement fixation tests
 Neutralization tests
 Labelled immunoassays
 Immunofluorescence
 Radio immunoassay
 Enzyme linked immunosorbent assay (ELISA)

69. Precipitation reactions
 Precipitation – when a soluble antigen
combines with its antibody – antigen
antibody complex forms an insoluble ppt in
the medium

70. Prozone

71.  Ring test – to group streptococci

72.  Slide test – VDRL for syphilis
 Tube test – Widal test

73. Agglutination reactions
 For blood grouping

75. Labelled immunoassays

76. Radio immuno assay

77. ELISA
 HIV

79. HYPERSENSITIVITY
REACTIONS
(ALLERGY)
.

80. Definition
• Hypersensitivity – exaggerated immune
response
• Allergen – substance which causes
hypersensitivity

81. • Hypersensitivity reaction occurs after
second exposure to antigen
• First exposure causes sensitisation

82. Types
• Based on time between second exposure
and clinical reaction –
– Immediate hypersensitivity
– Delayed hypersensitivity

83. Types
• Type I – anaphylactic
• Type II – cytotoxic
• Type III – immune complex
• Type IV – delayed type

84. Type I hypersensitivity (Allergy)
• a/k/a anaphylaxis (ana – without, phylaxis
– protection)

85. degranulation
• Releases histamine, serotonin, cytokines
and prostaglandins
• These cause
– Smooth muscle contraction (larynx, lungs)
– Leaky blood vessels (rhinorrhoea, oral
secretions)
– Intestinal fluid secretion (diarrhoea and
vomitting)

86. • Systemic anaphylaxis is fatal within
minutes
• Unless given adrenaline immediately

87. allergens
• Nuts
• Seafood
• Eggs
• Insect venom
• Drugs

88. Atopy
• Anaphylaxis in a localised area
• Eg asthma, hay fever
• Allergens here include
– Dust
– Pollen
– Eggs
– milk

89. TYPE II HS
• Mediated by IgG or IgM (with complement)
antibodies
• Examples are autoimmune hemolytic
anemias and hemolytic disease of
newborn

91. Type III HS
• Complexes of antigen and antibody get
deposited in various sites of the body like
– Kidneys
– Joints
– Skin
– Eye

92. • Examples
– Vasculitis
– Arthus reaction
– Serum sickness

95. Type IV HS
• Take 2-3 days to occur
• Delayed HS
• Mediated by T cells – antibodies not
involved
• Examples
– Tuberculin reaction
– Contact dermatitis

96. Tuberculin reaction
(Montaux test)
• To know whether the person is infected by
TB
• Injection of PPD into skin
• Look for raised area (induration) after 48
hours

99. Contact dermatitis
• Skin reaction caused by application of
various chemicals such as nickel,
chromium, drugs such as penicillin and
toiletries.

100. Contact dermatitis

101. Granulomatous reactions
• Occur due to intracellular pathogens such
as Mycobacteria, fungi and Leishmania
• Phagocytes are unable to remove and
digest them and become giant cells with
multiple nuclei

103. Summary

104. VACCINES AND
IMMUNISATION

105. Immunising agents
• Vaccines (active – slower, long lasting)
• Immunoglobulins (passive – faster, short
lasting)

106. Vaccine
• Substance designed to induce production
of antibodies against a specific disease
causing organism

107. Types
• Live – live but attenuated organisms
– Eg BCG, oral typhoid vaccine, oral polio
vaccine
• Killed – typhoid, cholera, injectable polio
vaccine
• Toxoids - DPT

108. Immunoglobulins (Passive)
• Administering directly antibodies
• Newborns receive passive immunisation
from colostrum
• Eg – Hep B antibodies given after
accidental exposure
• Protect immunodeficient individuals

109. Vaccines available

110. Herd immunity

111. Contact immunity
• Children immunised with live OPV shed
virus in feces
• An unimmunised family member /
community member who is exposed to this
shed virus develops immunity as well

112. National immunisation schedule
(Indian academiy of Paediatrics)

113. Optional immunisation
• Chicken pox
• Influenzae
• HPV
• Yellow fever
• Japanese encephalitis
• Pneumococcal vaccine