IMMUNITY- ENGLISH
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IMMUNITY
Immunity is the capability of multicellular organisms (
i.e. human being) to resist harmful microorganisms from entering their
cells. It is also known as Host Defense. The most important physiologic
function of the immune system is to prevent or eradicate infections .The study
of immunity is known as immunology.
CLASSIFICATION
Basically
immunity is classified in two types-
1.Innate Immunity
(Nonspecific Immunity)- Innate immunity,
also called natural immunity or native immunity, is always present in healthy
individuals (hence the term innate), prepared to block the entry of
microbes and to rapidly eliminate microbes that do succeed in entering host
tissues. It is non specific, means it acts against all the pathogens.
The innate
immune system is essentially made up of barriers that aim to keep
viruses, bacteria, parasites, and other foreign particles out of your body or
limit their ability to spread and move throughout the body. The innate immune
response is able to combat microbes immediately upon infection
The innate
immune system includes following components-
Physical defense
system
Chemical defense
system
Cellular defense
system
Physical defense system includes:
Skin acts as
physical barrier against entry of microorganisms into our body. Mucus membrane
is also a physical barrier but is less stronger than skin. If there is cut ,
wound or skin infection than microbes can enter into our body. It is first line
of defense and acts as strong fort against invaders.
The Chemical defense system includes :
Antimicrobial peptides and cytokines produced by skin,
sebaceous glands associated with hair follicles produce large amounts of fatty
acids which create an acidic environment that is hostile to microorganisms.
Acid produced by stomach and lysozyme present in tears and saliva also acts as
chemical defense as they are able to destroy pathogens.
Cellular defense system
There are many
types of white blood cells, or leukocytes, that work to defend and
protect the human body. The following cells are leukocytes of the innate immune
system:
Phagocytes, or Phagocytic cells: Phagocyte means
“eating cell”, which describes what role phagocytes play in the immune
response. Phagocytes circulate throughout the body, looking for potential
threats, like bacteria and viruses, to engulf and destroy.
Macrophages: Macrophages, can leave the circulatory system by
moving across the walls of capillary vessels. The ability to roam outside of
the circulatory system is important
Mast cells: Mast cells are found in mucous membranes and
connective tissues, and are important for wound healing and defense against
pathogens via the inflammatory response.
Neutrophils: Neutrophils are phagocytic cells that are also
classified as granulocytes because they contain granules in
their cytoplasm. These granules are very toxic to bacteria and fungi, and cause
them to stop proliferating or die on contact.
Eosinophils: Eosinophils are granulocytes target multicellular
parasites. Eosinophils secrete a range of highly toxic proteins and free
radicals that kill bacteria and parasites.
Basophils: Basophils are also granulocytes that attack
multicellular parasites. Basophils release histamine, much like mast cells.
Natural Killer
cells: Natural Killer cells (NK
cells), do not attack pathogens directly. Instead, natural killer cells destroy
infected host cells in order to stop the spread of an infection.
2.Acquired
Immunity
( Specific Immunity)- Acquired immunity, is acquired in the life time of a person by means of antigen-antibody
response. It is also called specific immunity because it is against a
particular or specific antigen (disease)
Antigen is a specific protein of microbes (bacteria, virus or
any other pathogen.)
Antibody is also a protein against the antigen produced by our
defense system.
acquired Immunity is further classified into two
types-
Ø
Active Immunity
(Active acquired Immunity)
Ø
Passive Immunity
(Passive acquired Immunity)
ACTIVE IMMUNITY- This type of immunity is acquired
actively by our immune system after exposure to pathogenic antigen naturally by
means of having infection and producing antibody against the particular antigen
and also artificially by getting vaccine against the particular disease and
producing antibody against the particular antigen (Our vaccination system is
based on this type of acquired immunity process)
The active immunity is further divided into two types
– Humoral immunity which is produced by B-Lymphocytes (lymphocytes produced by
bone marrow) which manufacture specific antibodies. Theses antibodies are
immunoglobulins known as – igG, igM, igA ,igD and igE.
Cell Mediated immunity which is produced by
T-Lymphocytes (lymphocytes produced by Thymus gland). T-Lymphocytes do not
manufacture antibodies but are responsible for recognition of antigen and
produce a chain of immune response after contact with the specific antigen
again.
PASSIVE INMMUNITY-
In passive immunity, an individual receives
antibodies from another individual who
is already immune to an infection. Passive immunity is therefore useful for
rapidly getting immunity even before the individual is able to mount an active
response, but it does not induce long-lived resistance to the infection.
Example of passive immunity is seen in newborns, whose immune systems are not
mature enough to respond to many pathogens but who are protected against
infections by acquiring antibodies from their mothers through the placenta and
breast milk (Natural passive immunity)
Clinically,
passive immunity is limited to treatment of some immunodeficiency diseases with
antibodies pooled from multiple donors, and for emergency treatment of some
viral infections and snakebites by using anti-serum(artificial passive
immunity). Plasma therapy is based on this types of immunity. So we can
understand that When the antibodies produced in one body (human or animal) and
transferred to another body to help fight against infection it is known as
passive immunity. In other words it is a
readymade immunity.
HERD
IMMUNITY-
Herd immunity
occurs when a large portion of a community (the herd) becomes immune to a
disease, naturally by getting infected and recovered or artificially by getting
vaccine, making the spread of disease from person to person unlikely. As a
result, the whole community becomes protected. Herd immunity is defined as the
resistance to the spread of a contagious disease within a population when
sufficiently high proportion of individuals are immune to the disease.
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