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1. Immunity
Dr. Himanshu Khatri

2. • Definition: Resistance exhibited by the host
towards microorganisms or their products

3. Types of immunity
• Innate (native)
• Acquired (adaptive)

4. Innate immunity
• First line of defence
• Depends of genetic or constitutional make-up
i.e. inborn
• No prior contact with microorganism, or
immunization
• Usually non-specific
• Immunological memory is absent no
improvement after re-exposure of the same
organism

5. Innate immunity
• Species immunity: All members of the same
species have similar susceptibility to a pathogen.
For e.g. humans are totally immune to canine
distemper
• Racial immunity: Different races of the same
species have different susceptibilty to a
pathogen. For e.g. African americans are more
susceptible to tuberculosis than Caucasians
• Individual immunity: Every individual has a
different susceptibility to a pathogen

6. Factors affecting innate immunity
• Age
• Hormonal influences
• Nutrition

7. Age
• The very young are more susceptible to
infections due to an immature immune system
• But the foetus and newborns (till 6 months of
age) are protected by maternal IgG antibodies
• The very old are also susceptible to infections
due to a waning of immune response
• Some infections like chickenpox are more
severe in adults

8. Hormonal influences
• Glucorticoids suppress immune response
primarily due to their anti-inflammatory
properties
• Increased susceptibility of infection in diabetes
mellitus (due to increased glucose and
glucocorticoids)
• Increased susceptibility of infection in adrenal
dysfunction like Cushing’s syndrome (due to
increased glucocorticoids)
• Increased susceptibility of infection during
pregnancy (due to increased glucocorticoids)

9. Nutrition
• Malnutrition increases susceptibility to
infections

10. Mechanisms of innate immunity
• Epithelial surfaces
• Antimicrobial substances in blood and tissues
• Microbial antagonisms
• Cellular factors
• Inflammation
• Fever
• Acute phase proteins
• Toll-like receptors

11. Epithelial surfaces
• Skin
• Respiratory tract
• Gastro-intestinal tract
• Conjunctiva
• Urinary tract
• Genital tract

12. Skin
• Intact skin and mucous membrane act as a
mechanical barrier
• Hence, breaks in the skin like abrasions or
wounds, bites of insects, or percutaneous
needle stick injury can introduce pathogens
into the body
• Sebum secreted by sebaceous glands is acidic
maintains pH of skin between 3 and 5 low
pH inhibits growth of many organisms

13. Respiratory tract
• Mucous is a viscous fluid which traps the
microorganisms in the respiratory tract and
moves them towards the pharynx
• Cilia are hair like protrusions of the epithelial cells
which sweep the microorganisms entrapped in
the mucous of the respiratory tract towards the
pharynx
• Cough reflex, stimulated by excessive secretions,
is an important defence mechanism

14. Gastro-intestinal tract
• Saliva has substances like lysozyme, which has
an inhibitory effect on microorganisms
• Many microorganisms are destroyed by the
low acidity in the stomach
• Those that survive the acidity are destroyed
by the high alkalinity in the duodenum
• Mucous present in the intestines traps the
organisms, and is subsequently removed by
peristalsis

15. Conjunctiva
• Flushing action of lachrymal secretions is an
important defence mechanism
• Tear has substances like lysozyme which has
an inhibitory effect on microorganisms

16. Urinary tract
• Flushing action of urine is an important
defence mechanism

17. Genital tract
• Lactobacilli in the vagina produce lactic acid
pH is low low pH is inhibitory for
microorganisms

18. Antimicrobial substances in blood and
tissues
• Lysozyme
• Complement system
• Interferon
• Acute phase proteins like C-reactive protein
(CRP)

19. Lysozyme
• Nearly present in all secretions except
cerebrospinal fluid, sweat, and urine
• Breaks down the peptidoglycan layer, which is
an important component of Gram-positive
bacteria
• Inhibitory against some Gram-positive
bacteria

20. Complement system
• Complement system is a group of cascading
proteins present in the blood, which on
activation, bring about important effector
functions like destruction of cell wall,
opsonization, etc.

21. Interferon
• Belong to a group of proteins called cytokines
• Usually produced by cells on induction by
viruses and other inducers
• Do not act on inducers themselves, but act on
other cells and activate them to produce
substances which inhibit multiplication of
viruses and other inducers

22. C-reactive protein (CRP)
• Produced during acute inflammation in the
liver
• Binds to bacteria activates complement
system phagocytosis of bacteria

23. Microbial antagonisms
• Epithelial surfaces have resident microbial
flora, which prevent colonization by
pathogens
• Resident flora are present on skin, oral cavity,
pharynx, intestines, vagina, etc.

24. Cellular factors
• Phagocytic cells like the neutrophils and macrophages
are an important component of innate immunity
• Macrophages are derived from the monocytes in
blood, and are the wandering amoeboid cells found in
tissues
• Phagocytic cells identify the non-specific components
of microbes with the help of Toll-like receptors (TLRs)
• Natural killer (NK) cells are the other group of cells of
innate immunity, and are active against viruses and
tumour cells
• The above cells are also a part of adaptive immunity

25. PHAGOCYTOSIS

26. Inflammation
• Increased vascular permeability during
inflammation causes plasma to outflow into
the tissues, and dilute the toxic products
present in the tissues
• The fibrin barrier serves to wall off the site of
infection

27. Fever
• Can directly destroy the pathogen
• Interferon production is increased at higher
temperature increased killing of pathogens

28. Acquired immunity
• It is the immunity which the individual
acquires during life

29. Innate immunity Acquired immunity
Inborn Acquired during life
No prior contact with
antigen
Contact with antigen
required
Usually non-specific Specific for an antigen
Immunological
memory is absent 
no improvement on
secondary exposure to
the same antigen
Immunological
memory may be
present  secondary
response is quicker and
stronger

30. Some common definitions
• Antigen: is a substance, which when introduced
into the body, induces an immune response
• Vaccines are biological preparations (of
microorganisms, their components, or their
products), which are immunogenic, but not
toxigenic
• Antibodies are a group of proteins belonging to
the immunoglobulin family, synthesized in the
body, and which react with the homologous
antigens. Antibodies belong to one of the five
classes: IgG, IgA, IgM, IgE, and IgD (GAMED)

31. • Active immunity is of two types:
1. Active
2. Passive

32. ACTIVE IMMUNITY PASSIVE IMMUNITY
Active functioning of host’s immune
system
Active functioning of host’s immune
system is absent
Induced by antigen (infection or
immunization)
Readymade antibody is transferred
Develops after a latent period (needed
for activation of immune response)
Immediate immunity
Negative phase may be present (during
which antigen combines with antibody,
and lowers its level in circulation)
Negative phase is absent
Long-lasting Lasts only till antibodies are
catabolised
Immunological memory is present Immunological memory is absent
Secondary response (on exposure to the
same antigen) is quicker and stronger
When an antibody is administered for
a second time, it is eliminated more
rapidly than initially

33. Active immunity
• Natural
• Artificial

34. Natural active immunity
• After an infection
• Strength and duration of immunity depends
on the pathogen
• In certain infections like measles, immunity is
lifelong
• Premunition: Immunity lasts only as long as
the infection is present, e.g. syphilis
• Effective immunity may be absent in some
infections like chancroid caused by H. ducreyi

35. Artificial active immunity
• After immunization with vaccines
• Vaccines can be either live attenuated, killed, sub-
unit, or products of microorganisms (e.g. toxoids)
• Live attenuated vaccines > effective than killed
vaccines > effective than sub-unit/products of
microorganisms
• Booster doses may be required for killed
vaccines/sub-unit vaccines/ toxoids
• Efficacy of vaccines can be increased by addition
of adjuvants like aluminium phosphate

36. Passive immunity
• Natural
• Artificial

37. Natural passive immunity
• Transfer of IgG antibodies from mother to the
foetus through the placenta.
• Passive immunity protects the infant in the first
few months (around 6) of life against infections
• Also, active immunization of mother can passively
protect the foetus against some infections like
tetanus
• Transfer of IgA antibodies from the mother to the
infant through milk is another example of natural
passive immunity

38. Artificial passive immunity
• Passive transfer of antibodies collected from
sensitized animals (usually horses) or humans
• Disadvantages of equine sera: hypersensitivity
(due to foreign protein) and immune
elimination (due to immune response against
foreign protein)
• Disadvantages of human sera: risk of
transmission of Hepatitis B, HIV, Hepatitis C,
etc.

39. Local immunity
• It is the immunity at particular mucosal surfaces
(e.g. gastro-intestinal or respiratory), which are
the site for entry and multiplication of pathogens
• IgA antibodies, which are secreted locally at these
sites, play an important role
• Certain vaccines, like that for polio or influenza,
can be given orally or intranasally respectively to
stimulate the respective local immunity

40. Herd immunity
• It is the overall level of immunity in the
community
• Eradication of a communicable disease
requires a high level of herd immunity
• When herd immunity is low, epidemics can
occur

41. THANK YOU