8)Host Defenselessandsom eonesocial.ppt

Social attitudes and environmental awareness will lead to a reduction in private vehicle use and a fall in the number of vehicles on long road

1. HOST DEFENCESHOST DEFENCES

2. What is the definition of host What is the definition of host
defense mechanism?defense mechanism?
Host defenses that protect against infection Host defenses that protect against infection
include:include:
 Natural barriersNatural barriers (e.g., skin, mucous (e.g., skin, mucous
membranes) membranes)
Nonspecific immune responses (e.g., Nonspecific immune responses (e.g.,
phagocytic cells (neutrophils, macrophages) phagocytic cells (neutrophils, macrophages)
and their products)and their products)
 Specific immune responses (e.g., Specific immune responses (e.g.,
antibodies, lymphocytes)antibodies, lymphocytes)

3. Lines of defenseLines of defense
The body has three lines of defense:The body has three lines of defense:




Physical Barriers.Physical Barriers.




Defensive Cells & Proteins, Defensive Cells & Proteins,
Inflammation, and Fever.Inflammation, and Fever.




The Immune System. The Immune System.

4. The First Line of Defense
These are a combination of These are a combination of
physical and chemical barriers physical and chemical barriers
that prevent all types of foreign that prevent all types of foreign
agents from penetrating the agents from penetrating the
outer layer of the body. outer layer of the body.
No specific foreign agent is No specific foreign agent is
targeted at this level.targeted at this level.

5. Physical Barriers
SkinSkin
 Cells filled with keratin, making Cells filled with keratin, making
skin impenetrable, waterproof, skin impenetrable, waterproof,
and resistant to disruptive toxins and resistant to disruptive toxins
and most invaders.and most invaders.
 Dead cells are shed and Dead cells are shed and
replaced (1 million every 40 replaced (1 million every 40
min), taking microbes with them.min), taking microbes with them.

6. Mucous MembranesMucous Membranes
The inner surfaces of the body are guarded by The inner surfaces of the body are guarded by
mucous membranes that line the respiratory, mucous membranes that line the respiratory,
digestive, urinary, and reproductive systems digestive, urinary, and reproductive systems
and protect the internal lining.and protect the internal lining.
 But, mucous membranes are more vulnerable But, mucous membranes are more vulnerable
than skin.than skin.
 Hair in the nose act as a coarse filter. Hair in the nose act as a coarse filter.

7. Chemical Barriers
Sweat produced by glands in the skin wash Sweat produced by glands in the skin wash
away microbes and their acidity slows away microbes and their acidity slows
bacterial growth.bacterial growth.
 Mucous membranes produce sticky mucous Mucous membranes produce sticky mucous
that traps many microbes.that traps many microbes.

8. Saliva and tears contain an enzyme called Saliva and tears contain an enzyme called
lysozyme that kills bacteria by rupturing lysozyme that kills bacteria by rupturing
their cell walls.their cell walls.
Cerumen (ear wax) – produced in the ear Cerumen (ear wax) – produced in the ear
canal and protects the canal by trapping dirt canal and protects the canal by trapping dirt
and dust particlesand dust particles

9. The Second Line of Defense:
Defensive Cells
If a pathogen penetrates the first line of If a pathogen penetrates the first line of
defense, these cells play a role in inhibiting defense, these cells play a role in inhibiting
or destroying the pathogen before it harms or destroying the pathogen before it harms
the body.the body.

11. when a person is said to when a person is said to
be immune?be immune?
A person is said to be immune when he A person is said to be immune when he
possesses "specific protective antibodies or possesses "specific protective antibodies or
cellular immunity as a result of previous cellular immunity as a result of previous
infection or immunization, or is so infection or immunization, or is so
conditioned by such previous experience as conditioned by such previous experience as
to respond adequately to prevent infection to respond adequately to prevent infection
and/or clinical illness following exposure to and/or clinical illness following exposure to
a specific infectious agent“.a specific infectious agent“.

12. ADAPTIVE(SPECIFIC) SPECIFIC)
DEFENCESDEFENCES
The specific defences may be:The specific defences may be:
1. Active immunity1. Active immunity
(1) Humoral immunity(1) Humoral immunity
(2) Cellular immunity(2) Cellular immunity
(3) Combination of the above.(3) Combination of the above.

13. 2. Passive immunity2. Passive immunity
A type of immunity that occurs when a A type of immunity that occurs when a
person is given antibodies rather than person is given antibodies rather than
making them through his or her own immune making them through his or her own immune
systemsystem. For example, passive immunity . For example, passive immunity
occurs when a baby receives a mother's occurs when a baby receives a mother's
antibodies through the placenta or breast antibodies through the placenta or breast
milkmilk
..
Adaptive(specific) Defences

14. (1) Normal human lg
(2) Specific human lg
(3) Animal antitoxins or
antisera

15. 1. Active immunity1. Active immunity
It is the immunity which an individual It is the immunity which an individual
develops as a result of infection or by develops as a result of infection or by
specific immunization and is usually specific immunization and is usually
associated with presence of antibodies or associated with presence of antibodies or
cells having a specific action on the cells having a specific action on the
microorganism concerned with a particular microorganism concerned with a particular
infectious disease or on its toxin.infectious disease or on its toxin.

16. Active immunity may be Active immunity may be
acquired in 3 ways :acquired in 3 ways :
(a)following clinical infection, e.g., (a)following clinical infection, e.g.,
chickenpox, rubella and measles.chickenpox, rubella and measles.
(b) following subclinical or in apparent (b) following subclinical or in apparent
infection, e.g., polio and diphtheria. ·infection, e.g., polio and diphtheria. ·
(c) following immunization with an antigen (c) following immunization with an antigen
which may be a killed vaccine, a live which may be a killed vaccine, a live
attenuated vaccine or toxoid.attenuated vaccine or toxoid.

17. The immune responseThe immune response
(a)(a)Primary Response.Primary Response.
(b)(b)Secondary (Booster) Response.Secondary (Booster) Response.

18. Primary ResponsePrimary Response
When an antigen is administered for the first When an antigen is administered for the first
time to an animal or human who has never been time to an animal or human who has never been
exposed to it, there is exposed to it, there is a latent period a latent period of of
induction of 3 to 10 days before antibodies induction of 3 to 10 days before antibodies
appear in the blood.appear in the blood.
The antibody that is elicited first is entirely of The antibody that is elicited first is entirely of
the the lgMlgM type.(The lgM antibody titre rises type.(The lgM antibody titre rises
steadily during the next 2-3 days or more, steadily during the next 2-3 days or more,
reaches a peak level and then declines almost as reaches a peak level and then declines almost as
fast as it developedfast as it developed

19. Meanwhile, if the antigenic stimulus was Meanwhile, if the antigenic stimulus was
sufficient, sufficient, lgGlgG antibody appears in a few antibody appears in a few
days.days.
 lgG reaches a peak in 7-10 days and thenlgG reaches a peak in 7-10 days and then
gradually falls over a period of weeks or gradually falls over a period of weeks or
months.months.

20. There is production of what are known as There is production of what are known as
"memory cells" or "primed cells" by both B "memory cells" or "primed cells" by both B
and T lymphocytes. and T lymphocytes.
These cells are responsible for the These cells are responsible for the
"immunological memory" which becomes "immunological memory" which becomes
established after immunization.established after immunization.

21. •The nature and extent of primary response The nature and extent of primary response
to an antigen is determined by a number of to an antigen is determined by a number of
factors:factors:
 Dose of antigen.Dose of antigen.
 Nature of antigen.Nature of antigen.
 Route of administration.Route of administration.
 Adjuvants.Adjuvants.
 Nutritional status of the host.Nutritional status of the host.

22. Secondary (Booster) Secondary (Booster)
ResponseResponse
The response to a booster dose differs in a The response to a booster dose differs in a
number of ways from the primary response :number of ways from the primary response :
(1) shorter latent period.(1) shorter latent period.
(2) production of antibody more rapid.(2) production of antibody more rapid.
(3) antibody more abundant.(3) antibody more abundant.

23. (4) antibody response maintained at higher (4) antibody response maintained at higher
levels for a longer period of time, and levels for a longer period of time, and
(5) the antibody elicited tends to have a (5) the antibody elicited tends to have a
greater avidity or capacity to bind to the greater avidity or capacity to bind to the
antigen.antigen.

24. Humoral immunityHumoral immunity
Humoral immunity comes from Humoral immunity comes from
the B-cells (bone-marrow the B-cells (bone-marrow
derived lymphocytes) which derived lymphocytes) which
increase and manufacture and manufacture
specific antibodies after antigen specific antibodies after antigen
presentation by macrophagespresentation by macrophages

25. Immunoglobulins are divided Immunoglobulins are divided
into 5 main classes:into 5 main classes:
 lgG, lgG,
lgM, lgM,
lgA,lgA,
 lgD andlgD and
 lgE lgE

26. •The antibodies are specific, i.e., The antibodies are specific, i.e.,
they react with the same they react with the same
antigen which provoked their antigen which provoked their
production, or a closely related production, or a closely related
one.one.

27. Cellular immunityCellular immunity
cellular immunity plays a cellular immunity plays a
fundamental role in resistance fundamental role in resistance
to infection.to infection.
cellular immunity is responsible cellular immunity is responsible
for immunity against many for immunity against many
diseases including tuberculosis, diseases including tuberculosis,
brucellosis and also for the brucellosis and also for the
body's rejection of foreign body's rejection of foreign
material, such as skin grafts.material, such as skin grafts.

28. factors produce a fall factors produce a fall
immunityimmunity
many factors are involved in the many factors are involved in the
maintenance of immunity: maintenance of immunity:
Fatigue, Fatigue,
strange surroundings, strange surroundings,
change of diet,change of diet,
ingestion of drugs, andingestion of drugs, and
 emotional shockemotional shock

29. Passive Passive immunityimmunity
•When antibodies produced in When antibodies produced in
one body (human or animal) are one body (human or animal) are
transferred to another to induce transferred to another to induce
protection disease, it is known protection disease, it is known
as passive immunity.as passive immunity.
•Passive immunity may be Passive immunity may be
induced :induced :

30. (a)(a)by administration of an antibody-containing by administration of an antibody-containing
preparation (immune globulin or antiserum).preparation (immune globulin or antiserum).
(b) by transfer of maternal antibodies across the (b) by transfer of maternal antibodies across the
placenta.placenta.
Human milk also contains protective Human milk also contains protective
antibodies, (lgA).antibodies, (lgA).
•(c) by transfer of lymphocytes, to induce (c) by transfer of lymphocytes, to induce
passive cellular immunitypassive cellular immunity

31. Passive immunization is useful for Passive immunization is useful for
individual who cannot form individual who cannot form
antibodies, or for the normal host antibodies, or for the normal host
who takes time to develop antibodies who takes time to develop antibodies
following active immunizationfollowing active immunization..

32. Passive immunity differs from active Passive immunity differs from active
immunity in the following respects :immunity in the following respects :
(a) immunity is rapidly established(a) immunity is rapidly established
(b) immunity produced is only temporary (b) immunity produced is only temporary
(days to months) till the antibody is (days to months) till the antibody is
eliminated from the body. eliminated from the body.

33. Herd immunityHerd immunity
Herd immunity (or community Herd immunity (or community
immunity) describes a type of immunity) describes a type of
immunity that occurs when the immunity that occurs when the
vaccination of a portion of population vaccination of a portion of population
(or herd) provides protection to (or herd) provides protection to
unprotected individuals.unprotected individuals.

34. Elements which contribute to herd Elements which contribute to herd
immunity areimmunity are
(a) Occurrence of clinical (a) Occurrence of clinical
and subclinical infection in and subclinical infection in
the herd. the herd.
(b) Immunization of the (b) Immunization of the
herd, andherd, and
(c) Herd structure(c) Herd structure..

35. Herd immunityHerd immunity




Reduced probability of an individual Reduced probability of an individual
becoming infected when it is part of a becoming infected when it is part of a
vaccinated population. vaccinated population.




The chance of becoming infected in a The chance of becoming infected in a
population decreases with increasing population decreases with increasing
density of individuals being vaccinated. density of individuals being vaccinated.

36. Conti….Conti….




Protection by herd immunity applies to Protection by herd immunity applies to
vaccinated as well as unvaccinated individuals.vaccinated as well as unvaccinated individuals.




Proportion immune among individuals in a Proportion immune among individuals in a
population .population .




Particular threshold proportion of immune Particular threshold proportion of immune
individuals that should lead to a decline in individuals that should lead to a decline in
incidence of infection.incidence of infection.

37. Effects of Herd immunity


Protection of those without
immunity.
Evolutionary pressure.


Serotype replacement.


Eradication of diseases.

38. Types of Herd ImmunityTypes of Herd Immunity
Innate (Inherent) Herd Immunity: Innate (Inherent) Herd Immunity:
It is genetically determined physiological It is genetically determined physiological
changes with respect to antibody production changes with respect to antibody production
or other defense mechanism in a herd.or other defense mechanism in a herd.
 It does not depend on the previous exposure It does not depend on the previous exposure
of herd with infection or it may arise in a of herd with infection or it may arise in a
herd through prolonged exposure to an herd through prolonged exposure to an
infection or natural selection. infection or natural selection.

39. Acquired Herd Immunity: Acquired Herd Immunity:
It is a type of herd immunity where a It is a type of herd immunity where a
sufficient number of its members have sufficient number of its members have
actually been exposed naturally or artificially actually been exposed naturally or artificially
to infectious agents during their lifespan. This to infectious agents during their lifespan. This
kind of exposure may be made very early in kind of exposure may be made very early in
lifelife..

40. Advantages & Disadvantages Advantages & Disadvantages
of Herd Immunityof Herd Immunity
Potential for infection elimination. Potential for infection elimination.
Reduced risk of infection for those Reduced risk of infection for those
refusing vaccination.refusing vaccination.




Reduced risk of infection for those for Reduced risk of infection for those for
whom vaccination is contraindicated.whom vaccination is contraindicated.

41. DisadvantagesDisadvantages
Herd immunity generally applies Herd immunity generally applies
only to diseases that are contagious.only to diseases that are contagious.




Raise the average age of Raise the average age of
infection among those who are infection among those who are
infected (e.g. polio, rubella, etc., ).infected (e.g. polio, rubella, etc., ).