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Section | III Microbiology 269
Topic 9
Immunity
LONG ESSAY
Q. 1. Define and classify immunity. Discuss acquired 5. Once developed the active immunity is long lasting.
immunity. Following antigenic exposure it develops slowly over a
period of days or weeks but persists for a long time,
Ans.
usually for years.
The resistance exhibited by the host towards injury caused by 6. Active immunity is associated with immunological
microorganisms and their products is known as immunity. memory besides the development of humoral and cel-
Immunity may be classified into different types as follows: lular immunity.
7. It is more effective and confers better protection than
Innate or Native Immunity passive immunization.
8. Active immunity is of two types as follows:
a. Natural
Nonspecific Specific b. Artificial
9. Natural active immunity
a. It is acquired after the natural infection by the or-
Species Racial Individual Species Racial Individual ganisms or recovery from disease or subclinical
infection.
Acquired or Adaptive Immunity b. In large majority of cases, it occurs by subclinical
infections after repeated exposure to small doses of
the infecting organism which pass unnoticed.
Active Passive c. Subclinical attacks by pathogenic microorganisms
play important roles in preventing epidemics, e.g.
poliomyelitis, tuberculosis.
Natural Artificial Natural Artificial d. Natural active immunity may follow overt infec-
tions, e.g. smallpox.
e. Such immunity is usually long lasting.
ACQUIRED OR ADAPTIVE IMMUNITY 10. Artificial active immunity
1. The resistance that an individual acquires during life is a. It is the resistance produced by vaccination.
known as acquired immunity. b. Vaccines are the preparations of live attenuated
2. It is of two types as follows: or killed microorganisms or active materials de-
a. Active rived from the microorganisms (toxoids) used for
b. Passive immunization.
c. Examples of various vaccines are as follows:
i. Bacterial vaccines
I. Active Immunity
– Live: BCG, anthrax, plague, brucella vac-
1. It is the resistance developed by an individual as a re- cines
sult of an antigenic stimulus. – Killed: Cholera vaccine
2. It is also known as adaptive immunity as it represents – Subunit: Typhoid VI antigen
an adaptive response of the host to a specific pathogen – Bacterial products: Tetanus toxoid
or other antigen. ii. Viral vaccines:
3. It usually follows either natural infection or vaccina- – Live: Oral polio vaccine (sabin), smallpox,
tion. It involves active functioning of the person’s im- measles, influenza and mumps
mune apparatus leading to the synthesis of antibodies – Killed: Injectable polio vaccine (salk)
and production of immunologically active cells. – Subunit : Hepatitis B vaccine
4. It develops only after a latent period. iii. Toxoids: Tetanus, diphtheria
,Click here to Visit - www.thedentalhub.org.in
270 Quick Review Series: BDS 2nd Year
They are prepared by inactivating the bacterial exotox- The agents used for this purpose are as follows:
ins by formalin or alum so that immunogenicity is retained 1. Hyperimmune sera of animal or human origin
but not toxigenicity. 2. Convalescent sera
3. Pooled human gamma globulin
II. Passive Immunity These are used for prophylaxis and therapy.
1. Passive immunity is the resistance induced in the 1. Hyperimmune sera of animal or human origin: Animal
recipient by transfer of antibodies preformed against antitoxin serum is produced by injection of toxoid into
infective agent or toxin in another host. horses in increasing doses till the blood is rich in circu-
2. The immune system plays no active role and the protec- lating antibodies.
tive mechanism comes into force immediately after Equine hyperimmune sera like antitetanus serum and
transfer of antibodies or immune serum. ATS prepared from hyperimmunized horses used to be
3. Passive immunization lasts for a short period and is in- employed extensively.
dicated for immediate and temporary protection in a They gave temporary protection but carried the risk of
nonimmune host faced with the threat of infection. hypersensitivity and immune elimination.
4. It is useful when instant immunity is required. Nowadays antisera of animal origin are recommended
5. Passive immunity is of two types as follows: only where human preparations are not available, for
a. Natural example: Antibotulism and polyvalent antigas gangrene
b. Artificial sera, antivenoms, equine antisera against diphtheria.
2. Convalescent sera: Sera of the patients recovering from
infectious diseases containing high levels of specific
a. Natural Passive Immunity antibody.
It is the resistance transferred from the mother to fetus or 3. Pooled human immunoglobulin (gamma globulins from
infant. pooled sera of healthy adults): It is prepared from plasma
Example: Transfer of maternal IgG to fetus transplacentally pools of healthy adults containing high levels of antibod-
or transfer of maternal IgA to infant through colostrums ies against all common pathogens prevalent in the region.
(first milk of mother after delivery) which gives protection Convalescent sera and pooled human gamma globulins
to neonates. were used for passive immunization against some viral
infections like viral hepatitis A.
The half-life of human immunoglobulin is 26 days and the
b. Artificial Passive Immunity
effect of passive immunization may last for 3–4 months.
It is the resistance passively transferred to a recipient by the Human gammaglobulins are used in treatment of pa-
administration of antibodies. tients with some immunodeficiencies.
SHORT ESSAYS
Q. 1. Classify immunity and describe active immunity period of days or weeks but persists for a long time,
with example. usually for years.
l Active immunity is associated with immunological
Ans.
memory besides the development of humoral and cel-
l Active immunity is a type of acquired immunity and is lular immunity.
the resistance developed by an individual as a result of l Active immunity develops either in form of humoral or
an antigenic stimulus. cell mediated or both.
It is also known as adaptive immunity as it represents an
Humoral or Antibody-mediated Immunity
l
adaptive response of the host to a specific pathogen or
other antigen. l It depends upon the active production of the antibodies
l It usually follows either natural infection or vaccination. against the antigens by the plasma cells.
It involves active functioning of the person’s immune l The specific circulating antibodies in the host combine
apparatus leading to the synthesis of antibodies and specifically with the corresponding antigens and modify
production of immunologically active cells. their activity.
l It develops only after a latent period. l Thus antigen molecules or particles may be clumped or
l Once developed the active immunity is long lasting. lysed, their toxins may be neutralized and readily re-
Following antigenic exposure it develops slowly over a moved after phagocytosis by neutrophils or macrophages.
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Section | III Microbiology 271
l Tissue invasion by virus particles may be prevented by Acquired or Adaptive Immunity
neutralizing activity of antiviral antibody.
Cell-mediated Immunity Active Passive
l It mainly depends on the specifically developed T cells by
certain antigens. The sensitized T lymphocytes are impor- Natural Artificial Natural Artificial
tant in resistance to chronic bacterial infections character-
ized by intracellular parasitism like TB, brucellosis, leprosy
and also in some viral diseases like herpes simplex. Active Immunity
l Active immunity is of two types as follows: 1. It is the resistance developed by an individual as a result
a. Natural of an antigenic stimulus.
b. Artificial 2. It is also known as adaptive immunity as it represents an
l Natural active immunity adaptive response of the host to a specific pathogen or
1. It is acquired after the natural infection by the organ- other antigen.
isms or recovery from disease or subclinical infection. 3. It usually follows either natural infection or vaccination.
2. In large majority of cases, it occurs by subclinical It involves active functioning of the person’s immune
infections after repeated exposure to small doses of apparatus leading to the synthesis of antibodies and
the infecting organism which pass unnoticed. production of immunologically active cells.
3. Subclinical attacks by pathogenic microorganisms 4. It is more effective and confers better protection than
play important roles in preventing epidemics. For passive immunization.
example: Poliomyelitis, tuberculosis. 5. Active immunity is of two types as follows:
4. Natural active immunity may follow overt infec- a. Natural
tions. Example: Smallpox b. Artificial
5. Such immunity is usually long lasting. 6. Natural active immunity
l Artificial active immunity a. It is acquired after the natural infection by the organ-
a. It is the resistance produced by vaccination. isms or recovery from disease or subclinical infec-
b. Vaccines are the preparations of live attenuated or tion. Examples: Poliomyelitis, tuberculosis.
killed microorganisms or active materials derived 7. Artificial active immunity
from the microorganisms (toxoids) used for immuni- a. It is the resistance produced by vaccination.
zation. Examples of various vaccines are as follows: b. Vaccines are the preparations of live attenuated or
i. Bacterial vaccines killed microorganisms or active materials derived from
– Live: BCG, anthrax, plague, brucella vaccines the microorganisms (toxoids) used for immunization.
– Killed: Cholera vaccine c. Examples of various vaccines are as follows:
– Subunit: Typhoid VI antigen i. Bacterial vaccines:
– Bacterial products: Tetanus toxoid – Live: BCG, anthrax, plague, brucella vaccines
ii. Viral vaccines – Killed: Cholera vaccine
– Live: Oral polio vaccine (sabin), smallpox, – Subunit: Typhoid VI antigen
measles, influenza and mumps – Bacterial products: Tetanus toxoid
– Killed: Injectable polio vaccine (salk) ii. Viral vaccines
– Subunit: Hepatitis B vaccine – Live: Oral polio vaccine (sabin), smallpox,
iii. Toxoids: Tetanus, diphtheria measles, influenza and mumps
They are prepared by inactivating the bacterial exotoxins by – Killed: Injectable polio vaccine (salk)
formalin or alum so that immunogenicity is retained but not – Subunit : Hepatitis B vaccine
toxigenicity. iii. Toxoids: Tetanus, diphtheria
Active immunity is more effective and confers better
protection than passive immunization.
Passive Immunity
Q. 2. Describe briefly about acquired immunity. l Passive immunity is the resistance induced in the recipi-
Ans. ent by transfer of antibodies preformed against infective
agent or toxin in another host.
l The resistance that an individual acquires during life is l The immune system plays no active role and the protec-
known as acquired immunity. tive mechanism comes into force immediately after
l It is of two types: active and passive. transfer of antibodies or immune serum.
Section | III Microbiology 269
Topic 9
Immunity
LONG ESSAY
Q. 1. Define and classify immunity. Discuss acquired 5. Once developed the active immunity is long lasting.
immunity. Following antigenic exposure it develops slowly over a
period of days or weeks but persists for a long time,
Ans.
usually for years.
The resistance exhibited by the host towards injury caused by 6. Active immunity is associated with immunological
microorganisms and their products is known as immunity. memory besides the development of humoral and cel-
Immunity may be classified into different types as follows: lular immunity.
7. It is more effective and confers better protection than
Innate or Native Immunity passive immunization.
8. Active immunity is of two types as follows:
a. Natural
Nonspecific Specific b. Artificial
9. Natural active immunity
a. It is acquired after the natural infection by the or-
Species Racial Individual Species Racial Individual ganisms or recovery from disease or subclinical
infection.
Acquired or Adaptive Immunity b. In large majority of cases, it occurs by subclinical
infections after repeated exposure to small doses of
the infecting organism which pass unnoticed.
Active Passive c. Subclinical attacks by pathogenic microorganisms
play important roles in preventing epidemics, e.g.
poliomyelitis, tuberculosis.
Natural Artificial Natural Artificial d. Natural active immunity may follow overt infec-
tions, e.g. smallpox.
e. Such immunity is usually long lasting.
ACQUIRED OR ADAPTIVE IMMUNITY 10. Artificial active immunity
1. The resistance that an individual acquires during life is a. It is the resistance produced by vaccination.
known as acquired immunity. b. Vaccines are the preparations of live attenuated
2. It is of two types as follows: or killed microorganisms or active materials de-
a. Active rived from the microorganisms (toxoids) used for
b. Passive immunization.
c. Examples of various vaccines are as follows:
i. Bacterial vaccines
I. Active Immunity
– Live: BCG, anthrax, plague, brucella vac-
1. It is the resistance developed by an individual as a re- cines
sult of an antigenic stimulus. – Killed: Cholera vaccine
2. It is also known as adaptive immunity as it represents – Subunit: Typhoid VI antigen
an adaptive response of the host to a specific pathogen – Bacterial products: Tetanus toxoid
or other antigen. ii. Viral vaccines:
3. It usually follows either natural infection or vaccina- – Live: Oral polio vaccine (sabin), smallpox,
tion. It involves active functioning of the person’s im- measles, influenza and mumps
mune apparatus leading to the synthesis of antibodies – Killed: Injectable polio vaccine (salk)
and production of immunologically active cells. – Subunit : Hepatitis B vaccine
4. It develops only after a latent period. iii. Toxoids: Tetanus, diphtheria
,Click here to Visit - www.thedentalhub.org.in
270 Quick Review Series: BDS 2nd Year
They are prepared by inactivating the bacterial exotox- The agents used for this purpose are as follows:
ins by formalin or alum so that immunogenicity is retained 1. Hyperimmune sera of animal or human origin
but not toxigenicity. 2. Convalescent sera
3. Pooled human gamma globulin
II. Passive Immunity These are used for prophylaxis and therapy.
1. Passive immunity is the resistance induced in the 1. Hyperimmune sera of animal or human origin: Animal
recipient by transfer of antibodies preformed against antitoxin serum is produced by injection of toxoid into
infective agent or toxin in another host. horses in increasing doses till the blood is rich in circu-
2. The immune system plays no active role and the protec- lating antibodies.
tive mechanism comes into force immediately after Equine hyperimmune sera like antitetanus serum and
transfer of antibodies or immune serum. ATS prepared from hyperimmunized horses used to be
3. Passive immunization lasts for a short period and is in- employed extensively.
dicated for immediate and temporary protection in a They gave temporary protection but carried the risk of
nonimmune host faced with the threat of infection. hypersensitivity and immune elimination.
4. It is useful when instant immunity is required. Nowadays antisera of animal origin are recommended
5. Passive immunity is of two types as follows: only where human preparations are not available, for
a. Natural example: Antibotulism and polyvalent antigas gangrene
b. Artificial sera, antivenoms, equine antisera against diphtheria.
2. Convalescent sera: Sera of the patients recovering from
infectious diseases containing high levels of specific
a. Natural Passive Immunity antibody.
It is the resistance transferred from the mother to fetus or 3. Pooled human immunoglobulin (gamma globulins from
infant. pooled sera of healthy adults): It is prepared from plasma
Example: Transfer of maternal IgG to fetus transplacentally pools of healthy adults containing high levels of antibod-
or transfer of maternal IgA to infant through colostrums ies against all common pathogens prevalent in the region.
(first milk of mother after delivery) which gives protection Convalescent sera and pooled human gamma globulins
to neonates. were used for passive immunization against some viral
infections like viral hepatitis A.
The half-life of human immunoglobulin is 26 days and the
b. Artificial Passive Immunity
effect of passive immunization may last for 3–4 months.
It is the resistance passively transferred to a recipient by the Human gammaglobulins are used in treatment of pa-
administration of antibodies. tients with some immunodeficiencies.
SHORT ESSAYS
Q. 1. Classify immunity and describe active immunity period of days or weeks but persists for a long time,
with example. usually for years.
l Active immunity is associated with immunological
Ans.
memory besides the development of humoral and cel-
l Active immunity is a type of acquired immunity and is lular immunity.
the resistance developed by an individual as a result of l Active immunity develops either in form of humoral or
an antigenic stimulus. cell mediated or both.
It is also known as adaptive immunity as it represents an
Humoral or Antibody-mediated Immunity
l
adaptive response of the host to a specific pathogen or
other antigen. l It depends upon the active production of the antibodies
l It usually follows either natural infection or vaccination. against the antigens by the plasma cells.
It involves active functioning of the person’s immune l The specific circulating antibodies in the host combine
apparatus leading to the synthesis of antibodies and specifically with the corresponding antigens and modify
production of immunologically active cells. their activity.
l It develops only after a latent period. l Thus antigen molecules or particles may be clumped or
l Once developed the active immunity is long lasting. lysed, their toxins may be neutralized and readily re-
Following antigenic exposure it develops slowly over a moved after phagocytosis by neutrophils or macrophages.
, Click here to Visit - www.thedentalhub.org.in
Section | III Microbiology 271
l Tissue invasion by virus particles may be prevented by Acquired or Adaptive Immunity
neutralizing activity of antiviral antibody.
Cell-mediated Immunity Active Passive
l It mainly depends on the specifically developed T cells by
certain antigens. The sensitized T lymphocytes are impor- Natural Artificial Natural Artificial
tant in resistance to chronic bacterial infections character-
ized by intracellular parasitism like TB, brucellosis, leprosy
and also in some viral diseases like herpes simplex. Active Immunity
l Active immunity is of two types as follows: 1. It is the resistance developed by an individual as a result
a. Natural of an antigenic stimulus.
b. Artificial 2. It is also known as adaptive immunity as it represents an
l Natural active immunity adaptive response of the host to a specific pathogen or
1. It is acquired after the natural infection by the organ- other antigen.
isms or recovery from disease or subclinical infection. 3. It usually follows either natural infection or vaccination.
2. In large majority of cases, it occurs by subclinical It involves active functioning of the person’s immune
infections after repeated exposure to small doses of apparatus leading to the synthesis of antibodies and
the infecting organism which pass unnoticed. production of immunologically active cells.
3. Subclinical attacks by pathogenic microorganisms 4. It is more effective and confers better protection than
play important roles in preventing epidemics. For passive immunization.
example: Poliomyelitis, tuberculosis. 5. Active immunity is of two types as follows:
4. Natural active immunity may follow overt infec- a. Natural
tions. Example: Smallpox b. Artificial
5. Such immunity is usually long lasting. 6. Natural active immunity
l Artificial active immunity a. It is acquired after the natural infection by the organ-
a. It is the resistance produced by vaccination. isms or recovery from disease or subclinical infec-
b. Vaccines are the preparations of live attenuated or tion. Examples: Poliomyelitis, tuberculosis.
killed microorganisms or active materials derived 7. Artificial active immunity
from the microorganisms (toxoids) used for immuni- a. It is the resistance produced by vaccination.
zation. Examples of various vaccines are as follows: b. Vaccines are the preparations of live attenuated or
i. Bacterial vaccines killed microorganisms or active materials derived from
– Live: BCG, anthrax, plague, brucella vaccines the microorganisms (toxoids) used for immunization.
– Killed: Cholera vaccine c. Examples of various vaccines are as follows:
– Subunit: Typhoid VI antigen i. Bacterial vaccines:
– Bacterial products: Tetanus toxoid – Live: BCG, anthrax, plague, brucella vaccines
ii. Viral vaccines – Killed: Cholera vaccine
– Live: Oral polio vaccine (sabin), smallpox, – Subunit: Typhoid VI antigen
measles, influenza and mumps – Bacterial products: Tetanus toxoid
– Killed: Injectable polio vaccine (salk) ii. Viral vaccines
– Subunit: Hepatitis B vaccine – Live: Oral polio vaccine (sabin), smallpox,
iii. Toxoids: Tetanus, diphtheria measles, influenza and mumps
They are prepared by inactivating the bacterial exotoxins by – Killed: Injectable polio vaccine (salk)
formalin or alum so that immunogenicity is retained but not – Subunit : Hepatitis B vaccine
toxigenicity. iii. Toxoids: Tetanus, diphtheria
Active immunity is more effective and confers better
protection than passive immunization.
Passive Immunity
Q. 2. Describe briefly about acquired immunity. l Passive immunity is the resistance induced in the recipi-
Ans. ent by transfer of antibodies preformed against infective
agent or toxin in another host.
l The resistance that an individual acquires during life is l The immune system plays no active role and the protec-
known as acquired immunity. tive mechanism comes into force immediately after
l It is of two types: active and passive. transfer of antibodies or immune serum.
