Chapter – 1.5
Defence Against Diseases. Production of
Monoclonal and Polyclonal Antibodies, Role of
B and T - Lymphocytes, Primary and Secondary
Immunity and Immunization. Hypersensitivity or
Allergic Reactions and Auto Immune Diseases
We are aware that to protect children from infectious diseases such as typhoid,
hepatitis, chicken pox, small pox, diphtheria etc they need to be vaccinated. The
recent immunization drive to eradicate polio is to save children form the
disease. It is a known fact that once a person contacts chicken pox he is not
likely to get it again. This is called immunity. The body has a wonderful system
called the, ‘immune system’ which guards us from succumbing to infections.
There are special cells that produce antibodies and some of them devour and
destroy the bacteria and virus to save us from further complications.
DEFENSE AGAINST DISEASES
Microorganisms are all round us. As they are not visible to the naked eye we do
not give them much importance. Many of the microorganisms are harmless but
some of them are pathogens. It is easy for the microorganisms to enter
unnoticed, causing various diseases and a lot of harm. Though we do fall ill
sometimes we are most of the time in good health. This is because the entry of
microorganisms can be checked. The body has a number of barriers that
restrict the entry of microorganisms. They can be divided into
a. Mechanical or anatomical barriers
b. Physiological barriers
c. Phagocytic barriers
d. Inflammatory response
a. Mechanical Barriers
Mechanical barriers are the skin and the lining of mucous membrane. The skin
that covers the body is the most important barrier, which can ward off the entry
of microorganisms even though there are pores of the sweat glands. The
secretions of the sweat glands and the sebaceous glands (oil glands) are acidic in
nature as they contain lactic acid and fatty acids. The skin has a pH of 3 to 5.
Most microorganisms do not survive in the acidic medium. If the skin is cut due
to injury or due to burns then infection sets in, as the microorganisms can enter.
There are several places through which the microorganisms can enter
such as the mouth, nose, vagina, urethra and anus. All these openings
,54 Defence Against Diseases…
produce mucous in which the bacteria can be trapped as they enter. In addition
to this the respiratory passage is lined by ciliated epithelium that sweeps
the microorganisms trapped in the mucous towards the pharynx. The reflex
action of coughing and sneezing removes them.
b. Physiological Barriers
The body produces several secretions capable of acting as barriers
preventing the entry of microorganisms
i. The mouth secretes saliva that contains antibacterial substances like
lysozyme, a hydrolytic enzyme that can destroy the cell wall of the bacteria.
ii. The ears secrete wax that blocks the entry of microorganisms.
iii. The vagina has no secretory glands but the surface is kept moist by cervical
secretions. The environment of the vagina is acidic, the pH is about 4.9 to
3.5. This is because the Lactobacillus acidophilus microbes are normally
present and they secrete lactic acid. The acidity inhibits the growth of
most microbes that may enter the vagina from the perianal region.
iv. The urethra is the opening through which urine is excreted. The action of
excretion washes away the microorganisms.
v. Tears help in washing away microorganisms. They also contain lysozyme
that kill the bacteria and keep the eyes free from infection.
vi. The gastric juice secreted by the stomach kill the bacteria that enter along
with the food.
vii. The semen contains spermine and zinc that kill the bacteria.
viii. The presence of colonies of non-pathogenic flora on the mucous
membrane does not allow the attachment of the pathogens.
Body temperature is one of the factors that act as a barrier as many pathogens
do not survive at normal body temperature. The onset of fever due to infections
prevents the growth of the pathogens.
All the above-mentioned barriers are effective and form the first line of defense.
In spite of this many microorganisms still manage to enter into our body.
Examples,
i. Bacteria that can metabolize sebum or the oil produced by the oil gland
live on the skin causing acne.
ii. Vectors that carry pathogens like mosquito pierce the skin and inject
plasmodium as it sucks blood. The flea causes bubonic plague.
iii. The virus that cause flu has a surface molecule that helps in attaching to
the mucous membrane of the respiratory tract. Thus the cilia in the tract
cannot dislodge it.
iv. The pathogen causing gonorrhea attaches itself to the mucous membrane
of the urinogenital tract by the help of hair like projections called pili. They
are able to attach themselves to certain glycoproteins on the membrane.
v. Urinary tract infections or vaginal infections caused by bacteria are
also common.
When the microorganisms gain entry, there are other means of
destroying the pathogens.
c. Phagocytic Barriers
, 55 Defence Against Diseases…
There are certain cells in the body that are capable of ingesting the
pathogens. The macrophages in the connective tissue, monocytes and
neutrophils engulf the pathogens and destroy them. The cells are capable of
phagocytosis and form a vesicle in which the pathogens are digested.
Production of certain chemicals that defend the body once the
microorganisms are inside.
Interferon
These are a group of proteins secreted by animal cells in response to a viral
infection. Issacs and Linderman discovered interferon in 1957. The name
interferon was given because of its property of interfering with or the blockage of
a viral infection. Interferon not only protects other cells from a particular viral
infection but also from other viral infections. Interferon is a glycoprotein, which
can be digested by proteolytic enzymes. Based on their physico-chemical
properties interferons are designated as, alpha, beta, and gamma interferons.
During a viral infection the virus binds to a receptor on the cell and transmits a
signal to the cell nucleus and this triggers a production of interferon. The
interferon produced is released into the intercellular spaces. This interferon
activates a gene complex in the neighboring cells inducing them to produce a
protein that interferes with viral multiplication and thus protects them from the
viral infection. Interferon confers temporary resistance to the neighboring cells
and thus limits the spread of the viral infection. The action of interferon is to
inhibit the energy required for viral multiplication.
Complement and collectins
Complement is a type of serum protein that exists in an inactive state. These are
a series of 20 proteins, when activated they lyse the pathogens or help in the
process of phagocytosis. Collectins are like complement and can kill the
pathogens by destroying their membranes or helping in phagocytosis.
Toll like receptors
Toll-like receptors are associated with cells. They are capable of recognizing the
liposaccharides on the Gram-negative bacteria. On entry of the bacteria the toll-
like receptors cause production of a number of molecules that causes
inflammation required to eliminate the bacteria.
d. Inflammatory Response
An inflammation is a sign of infection. The injured area turns, red, gets swollen,
there is an increase in temperature and there is pain, after some time pus
can be seen and later there is formation of a scab or scar tissue.
When the skin is cut or is damaged, the pathogens gain entry. Tissue damage
causes a release of vasoactive and chemotactic factors. This causes an increase
in the blood flow and an increase in the permeability of the capillaries. There is
vasodilation or an increase in the diameter of the capillaries supplying that
area and constriction of capillaries that drain the blood. The area becomes red
and there is an increase in temperature. The vasodilation increases the
permeability of the capillaries and there is movement of fluid and cells out of
the capillaries into the tissue. The fluid that accumulates is called exudate and
contains a number of proteins. The collection of fluid causes edema or
swelling.
Defence Against Diseases. Production of
Monoclonal and Polyclonal Antibodies, Role of
B and T - Lymphocytes, Primary and Secondary
Immunity and Immunization. Hypersensitivity or
Allergic Reactions and Auto Immune Diseases
We are aware that to protect children from infectious diseases such as typhoid,
hepatitis, chicken pox, small pox, diphtheria etc they need to be vaccinated. The
recent immunization drive to eradicate polio is to save children form the
disease. It is a known fact that once a person contacts chicken pox he is not
likely to get it again. This is called immunity. The body has a wonderful system
called the, ‘immune system’ which guards us from succumbing to infections.
There are special cells that produce antibodies and some of them devour and
destroy the bacteria and virus to save us from further complications.
DEFENSE AGAINST DISEASES
Microorganisms are all round us. As they are not visible to the naked eye we do
not give them much importance. Many of the microorganisms are harmless but
some of them are pathogens. It is easy for the microorganisms to enter
unnoticed, causing various diseases and a lot of harm. Though we do fall ill
sometimes we are most of the time in good health. This is because the entry of
microorganisms can be checked. The body has a number of barriers that
restrict the entry of microorganisms. They can be divided into
a. Mechanical or anatomical barriers
b. Physiological barriers
c. Phagocytic barriers
d. Inflammatory response
a. Mechanical Barriers
Mechanical barriers are the skin and the lining of mucous membrane. The skin
that covers the body is the most important barrier, which can ward off the entry
of microorganisms even though there are pores of the sweat glands. The
secretions of the sweat glands and the sebaceous glands (oil glands) are acidic in
nature as they contain lactic acid and fatty acids. The skin has a pH of 3 to 5.
Most microorganisms do not survive in the acidic medium. If the skin is cut due
to injury or due to burns then infection sets in, as the microorganisms can enter.
There are several places through which the microorganisms can enter
such as the mouth, nose, vagina, urethra and anus. All these openings
,54 Defence Against Diseases…
produce mucous in which the bacteria can be trapped as they enter. In addition
to this the respiratory passage is lined by ciliated epithelium that sweeps
the microorganisms trapped in the mucous towards the pharynx. The reflex
action of coughing and sneezing removes them.
b. Physiological Barriers
The body produces several secretions capable of acting as barriers
preventing the entry of microorganisms
i. The mouth secretes saliva that contains antibacterial substances like
lysozyme, a hydrolytic enzyme that can destroy the cell wall of the bacteria.
ii. The ears secrete wax that blocks the entry of microorganisms.
iii. The vagina has no secretory glands but the surface is kept moist by cervical
secretions. The environment of the vagina is acidic, the pH is about 4.9 to
3.5. This is because the Lactobacillus acidophilus microbes are normally
present and they secrete lactic acid. The acidity inhibits the growth of
most microbes that may enter the vagina from the perianal region.
iv. The urethra is the opening through which urine is excreted. The action of
excretion washes away the microorganisms.
v. Tears help in washing away microorganisms. They also contain lysozyme
that kill the bacteria and keep the eyes free from infection.
vi. The gastric juice secreted by the stomach kill the bacteria that enter along
with the food.
vii. The semen contains spermine and zinc that kill the bacteria.
viii. The presence of colonies of non-pathogenic flora on the mucous
membrane does not allow the attachment of the pathogens.
Body temperature is one of the factors that act as a barrier as many pathogens
do not survive at normal body temperature. The onset of fever due to infections
prevents the growth of the pathogens.
All the above-mentioned barriers are effective and form the first line of defense.
In spite of this many microorganisms still manage to enter into our body.
Examples,
i. Bacteria that can metabolize sebum or the oil produced by the oil gland
live on the skin causing acne.
ii. Vectors that carry pathogens like mosquito pierce the skin and inject
plasmodium as it sucks blood. The flea causes bubonic plague.
iii. The virus that cause flu has a surface molecule that helps in attaching to
the mucous membrane of the respiratory tract. Thus the cilia in the tract
cannot dislodge it.
iv. The pathogen causing gonorrhea attaches itself to the mucous membrane
of the urinogenital tract by the help of hair like projections called pili. They
are able to attach themselves to certain glycoproteins on the membrane.
v. Urinary tract infections or vaginal infections caused by bacteria are
also common.
When the microorganisms gain entry, there are other means of
destroying the pathogens.
c. Phagocytic Barriers
, 55 Defence Against Diseases…
There are certain cells in the body that are capable of ingesting the
pathogens. The macrophages in the connective tissue, monocytes and
neutrophils engulf the pathogens and destroy them. The cells are capable of
phagocytosis and form a vesicle in which the pathogens are digested.
Production of certain chemicals that defend the body once the
microorganisms are inside.
Interferon
These are a group of proteins secreted by animal cells in response to a viral
infection. Issacs and Linderman discovered interferon in 1957. The name
interferon was given because of its property of interfering with or the blockage of
a viral infection. Interferon not only protects other cells from a particular viral
infection but also from other viral infections. Interferon is a glycoprotein, which
can be digested by proteolytic enzymes. Based on their physico-chemical
properties interferons are designated as, alpha, beta, and gamma interferons.
During a viral infection the virus binds to a receptor on the cell and transmits a
signal to the cell nucleus and this triggers a production of interferon. The
interferon produced is released into the intercellular spaces. This interferon
activates a gene complex in the neighboring cells inducing them to produce a
protein that interferes with viral multiplication and thus protects them from the
viral infection. Interferon confers temporary resistance to the neighboring cells
and thus limits the spread of the viral infection. The action of interferon is to
inhibit the energy required for viral multiplication.
Complement and collectins
Complement is a type of serum protein that exists in an inactive state. These are
a series of 20 proteins, when activated they lyse the pathogens or help in the
process of phagocytosis. Collectins are like complement and can kill the
pathogens by destroying their membranes or helping in phagocytosis.
Toll like receptors
Toll-like receptors are associated with cells. They are capable of recognizing the
liposaccharides on the Gram-negative bacteria. On entry of the bacteria the toll-
like receptors cause production of a number of molecules that causes
inflammation required to eliminate the bacteria.
d. Inflammatory Response
An inflammation is a sign of infection. The injured area turns, red, gets swollen,
there is an increase in temperature and there is pain, after some time pus
can be seen and later there is formation of a scab or scar tissue.
When the skin is cut or is damaged, the pathogens gain entry. Tissue damage
causes a release of vasoactive and chemotactic factors. This causes an increase
in the blood flow and an increase in the permeability of the capillaries. There is
vasodilation or an increase in the diameter of the capillaries supplying that
area and constriction of capillaries that drain the blood. The area becomes red
and there is an increase in temperature. The vasodilation increases the
permeability of the capillaries and there is movement of fluid and cells out of
the capillaries into the tissue. The fluid that accumulates is called exudate and
contains a number of proteins. The collection of fluid causes edema or
swelling.
