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Immunity and
its types
Immunity is derived from Latin word “immunis” which means free from burden.
In this case burden refers to disease caused by microorganisms or their toxic
products.
Therefore Immunity is defined as the state of resistance or in susceptibility to
disease caused by particular microorganisms or their toxic products. For example
some individuals having genetic deficiency of glucose-6-phosphate dehydrogenase
are resistant to malaria. Such individuals are said to be immune to Plasmodium.

In biology, immunity is the balanced state of multicellular organisms having

adequate biological defenses to fight infection, disease, or other unwanted
biological invasion, while having adequate tolerance to avoid allergy,
and autoimmune diseases

Immunity is the capability of multicellular organisms to resist

harmful microorganisms from entering it. Immunity involves both specific and
nonspecific components. The nonspecific components act as barriers or eliminators
of a wide range of pathogens irrespective of their antigenic make-up. Other
components of the immune system adapt themselves to each new disease
encountered and can generate pathogen-specific immunity.

An immune system may contain innate and adaptive components. The innate
system in mammalians, for example, is composed of primitive bone marrow cells
that are programmed to recognise foreign substances and react. The adaptive
system is composed of more advanced lymphatic cells that are programmed to
recognise self-substances and don't react. The reaction to foreign s
ubstances is etymologically described as inflammation, meaning to set on fire. The
non-reaction to self-substances is described as immunity, meaning to exempt or as
immunotolerance. These two components of the immune system create a dynamic
biological environment where "health" can be seen as a physical state where the
self is immunologically spared, and what is foreign is inflammatorily and
immunologically eliminated. "Disease" can arise when what is foreign cannot be
eliminated or what is self is not spared.
History of theories
The concept of immunity has intrigued mankind for thousands of years. The
prehistoric view of disease was that supernatural forces caused it, and that illness
was a form of theurgic punishment for "bad deeds" or "evil thoughts" visited upon
the soul by the gods or by one's enemies.[1] Between the time of Hippocrates and
the 19th century, when the foundations of the scientific methods were laid,
diseases were attributed to an alteration or imbalance in one of the four
humors (blood, phlegm, yellow bile or black bile).[2] Also popular during this time
before learning that communicable diseases came from germs/microbes was
the miasma theory, which held that diseases such as cholera or the Black
Plague were caused by a miasma, a noxious form of "bad air".[1] If someone were
exposed to the miasma in a swamp, in evening air, or breathing air in a sickroom or
hospital ward, they could get a disease.

The modern word "immunity" derives from the Latin immunis, meaning
exemption from military service, tax payments or other public services.[3] The first
written descriptions of the concept of immunity may have been made by the
Athenian Thucydides who, in 430 BC, described that when the plague hit Athens:
"the sick and the dying were tended by the pitying care of those who had
recovered, because they knew the course of the disease and were themselves free
from apprehensions. For no one was ever attacked a second time, or not with a
fatal result".[3] The term "immunes", is also found in the epic poem "Pharsalia"
written around 60 B.C. by the poet Marcus Annaeus Lucanus to describe a North
African tribe's resistance to snake venom.[2]
The first clinical description of immunity which arose from a specific disease-
causing organism is probably Kitab fi al-jadari wa-al-hasbah ('A Treatise on
Smallpox and Measles', translated 1848[4]) written by the Islamicphysician Al-
Razi in the 9th century. In the treatise, Al Razi describes the clinical presentation
of smallpox and measles and goes on to indicate that exposure to these specific
agents confers lasting immunity (although he does not use this term).[2] The first
scientist who developed a full theory of immunity was Ilya Mechnikov after he
revealed phagocytosis in 1882. With Louis Pasteur's germ theory of disease, the
fledgling science of immunology began to explain how bacteria caused disease,
and how, following infection, the human body gained the ability to resist further
infections.[3]

Albert Edelfelt, Louis Pasteur in his laboratory, 18

Immunity and its types: Innate and Acquired immunity

Innate or Natural immunity:

 Immunity with which an individual is born is called innate or natural

immunity.

 Innate immunity is provided by various components such as Skin, mucus

membrane, Phagocytic cells etc

 Innate immunity acts as first line of defense to particular microorganisms.

Mechanism of innate immunity:

1. Anatomical barrier
2. Physicochemical barrier
3. Phagocytic barrier or Phagocytosis
4. Inflammatory barrier or Inflammation
Types of innate immunity:

1. Species immunity

2. Racial immunity

3. Individual immunity

1. Species immunity:
 If one species is resistant to certain infection and the other species is
susceptible to the same infection then it is called as species immunity.

 Anatomic, physiological and metabolic differences between species

determine species immunity. For example, Birds are resistant to anthrax but
Human are susceptible. It is simply because higher body temperature of
birds kills Bacillus anthracis.
 Anatomic differences between species also determine species immunity. For
example, Human are more susceptible to skin infection whereas Cattles are
more resistant to the same skin infection. It is because of tough and hairy
skin (hides) of Cattles.

2. Racial immunity:
 If one race is susceptible while other race is resistant to same infection, then
it is called Racial immunity.

 For examples; certain African race are more resistant to malaria and yellow
fever where are Asian or Americans are susceptible to same infection.
Similarly Orientals (East Asia) are relatively resistant to syphilis.

 Racial immunity is determined by difference in Socio-economic status,

habitat, culture feeding habits, environments, genetic, etc.
3. Individual immunity:
 If one individual of certain race or cast is resistant while other individuals of
same race or cast are susceptible to certain infection, then it is called as
individual immunity

 Individual immunity is determined by various factors such as health status,

nutritional status, previous illness, personal hygiene, genetic differences etc.

 For examples; Individual with genetic deficiency of glucose-6 phosphate

dehydrogenase are resistant to Malaria.
 As its name nonspecific suggests that it lacks specific responses to specific
invaders. Innate immunity or nonspecific immunity is well done by
providing different barriers to the entry of the foreign agents into our body.
Innate immunity consists of four types of barriers— physical, physiological,
cellular and cytokine barriers

1. Physical Barriers:
 They are mechanical barriers to many microbial pathogens. These are of two
types. Skin and mucous membrane.

(a) Skin:
 The skin is physical barrier of body. Its outer tough layer, the stratum
corneum prevents the entry of bacteria and viruses.

(b) Mucous Membranes:

 Mucus secreted by mucous membrane traps the microorganisms and
immobilises them. Microorganisms and dust particles can enter the
respiratory tract with air during breathing which are trapped in the mucus.
The cilia sweep the mucus loaded with microorganisms and dust particles
into the pharynx (throat). From the pharynx it is thrown out or swallowed for
elimination with the faeces.


 2. Physiological Barriers:
 The skin and mucous membranes secrete certain chemicals which dispose
off the pathogens from the body. Body temperature, pH of the body fluids
and various body secretions prevent growth of many disease causing
microorganisms. Some of the important examples of physiological barriers
are as follows:

 (a) Acid of the stomach kills most ingested microorganisms,

 (b) Bile does not allow growth of microorganisms,

 (c) Cerumen (ear wax) traps dust particles, kills bacteria and repels insects,

 (d) Lysozyme is present in tissue fluids and in almost all secretions except in
cerebrospinal fluid, sweat and urine. Lysozyme is in good quantity in tears
from eyes. Lysozyme attacks bacteria and dissolves their cell walls.
Lysoenzyme is also found in saliva,

 (e) Nasal Hair. They filter out microbes and dust in nose,

 (f) Urine. It washes microbes from urethra,

 (h) Sebum (sweat). It forms a protective acid film over the skin surface that
inhibits growth of many microbes
 3. Cellular Barriers:

 These are certain white blood corpuscles (leucocytes), macrophages, natural

killer cells, complement system, inflammation, fever, antimicrobial
substances, etc.

(i) Certain Leucocytes:

 Neutrophils and monocytes are major phagocytic leucocytes.

 (a) Polymorpho-nuclear Leucocytes (PMNL- neutrophils):

 As they have multiplied nucleus they are normally called
polymorphonuclear leucocytes (PMNL-neu- trophils). Neutrophils are short
lived and are highly motile phagocytic killers. Neutrophils are formed from
stem cells in the bone marrow. Neutrophils are the most numerous of all
leucocytes. They die after a few days and must therefore, be constantly
replaced. Neutrophils constitute about 40% to 75% of the blood leucocytes
in humans.

(b) Monocytes:
 They are the largest of all types of leucocytes and somewhat amoeboid in
shape. They have clear cytoplasm (without cytoplasmic granules). The
nucleus is bean-shaped. Monocytes constitute about 2-10% of the blood
leucocytes. They are motile and phagocytic in nature and engulf bacteria and
cellular debris. Their life span is about 10 to 20 hours. Generally they
change into macrophages after entering tissue spaces.
 (ii) Macrophages:
 Monocytes circulate in the bloodstream for about 8 hours, during which time
they enlarge and then migrate into the tissues and differentiate into specific
tissue macrophages. Macrophages are long lived and are highly motile
phagocytic.

(iii) Natural Killer Cells (NK Cells):

 Besides the phagocytes, there are natural killer cells in the body which are a
type of lymphocytes and are present in the spleen, lymph nodes and red bone
marrow. NK cells do not have antigen receptors like T cells and В cells. NK
cells cause cellular destruction in at least two ways:

 (a) NK cells produce perforins which are chemicals that when inserted into
the plasma membrane of a microbe make so weak that cytolysis (breakdown
of cells particularly their outer membrane) occurs and creates pores in the
plasma membrane of the target cells. These pores allow entry of water into
the target cells, which then swell and burst. Cellular remains are eaten by
phagocytes.
(iv) Complement (Fig. 8.7):
 Complement is a group of 20 proteins, many of which are enzyme
precursors and are produced by the liver. These proteins are present in the
serum of the blood (the fluid portion of the blood excluding cells and
clotting factors) and on plasma membranes. They are found circulating in
the blood plasma and within tissues throughout the body. They were named
complement by Ehrlich because they complement the actions of other
components of the immune system (e.g., action of antibody on antigen) in
the fight against infection. Jules Bordet is the discoverer of complement.
 (v) Inflammation:
 Inflammation is a defensive response of the body to tissue damage. The
conditions that may produce inflammation are pathogens, abrasions
(scraping off) chemical irritations, distortion or disturbances of cells, and
extreme temperatures. The signs and symptoms of inflammation are redness,
pain, heat and swelling.

 Inflammation can also cause the loss of function in the injured area,
depending on the site and extent of the injury.

 (vi) Fever:
 Fever may be brought about by toxins produced by pathogens and a protein
called endogenous pyrogen (fever producing substance), released by
macrophages. When enough pyrogens reach the brain, the body’s thermostat
is reset to a higher temperature, allowing the temperature of the entire body
to rise.

 Mild fever strengthens the defence mechanism by activating the phagocytes

and by inhibiting the growth of microbes. A very high temperature may
prove dangerous. It must be quickly brought down by giving antipyretics.
 4. Cytokine Barriers:
 Cytokines (Chemical messengers of immune cells) are low molecular weight
proteins that stimulate or inhibit the differentiation, proliferation or function
of immune cells. They are involved in the cell to cell communication. Kinds
of cytokines include interleukins produced by leucocytes, lymphocytes
produced by lymphocytes, tumour necrosis factor and interferon’s (IFNs).
Interferon’s protect against viral infection of cells.
Acquired or Developed immunity:

 Immunity which is developed later in life after microbial infection in host is

called as Acquired or developed immunity. For example, If an individual is
infected with chicken pox virus, he/she become resistant to same virus in
later life.

 Acquired immunity is provided by Antibodies and certain T-lymphocytes.

 Components of acquired immunity such as Antibodies and T- cells are

specific to particular microorganism. Therefore acquired immunity is also
known as Specific immunity.

Characteristics of Acquired immunity:

 Specificity

 Self/non-self recognition

 Immunological memory

 Diversity

Types of acquired immunity:

1. Active immunity

2. Passive immunity
 Components of Acquired Immunity:
 Acquired immunity has two components: humeral immunity or Antibody
mediated immune system (AMIS) and cellular immunity or cell mediated
immune system (CMIS).

I. Antibody Mediated Immune System (AMIS) or Humoral

Immunity:
 It consists of antibodies (specialised proteins produced in the body in
response to antigen) that circulate in the body fluids like blood plasma and
lymph. The word ‘humor’ pertains to fluid. В lymphocytes (B cells) produce
antibodies that regulate humoral immunity. The T-lymphocytes themselves
do not secrete anti-bodies but help В lymphocytes produce them.

II. Cell-Mediated Immune System (CMIS) or Т-Cell

Immunity:
 A healthy person has about a trillion lymphocytes. Lymphocytes are of two
types: T lymphocytes or T cells and В lymphocytes or В cells. As we know
both types of lymphocytes and other cells of the immune system are
produced in the bone marrow. The process of production of cells of immune
system in the bone marrow is called haematopoiesis.
Passive
 If host does not produce antibodies itself but antibodies produced in other
host provides immunity, than it is known as Passive immunity.

 It is of two types; natural passive immunity and Artificial passive immunity

 Natural passive immunity: IgG antibody produced in mother cross

placenta and protects fetus up to 6 month old age.
 Artificial passive immunity: if preformed antibody are injected into host
for immunity. Eg. Anti-venom, Rabies vaccine (* it is not a vaccine, it is
preformed anti rabies antibody).

Passive immunity is the transfer of active immunity, in the form of readymade

antibodies, from one individual to another. Passive immunity can occur naturally,
when maternal antibodies are transferred to the foetus through the placenta, and
can also be induced artificially, when high levels
of human (or horse) antibodies specific for a pathogen or toxin are transferred to
non-immune individuals. Passive immunization is used when there is a high risk of
infection and insufficient time for the body to develop its own immune response,
or to reduce the symptoms of ongoing or immunosuppressive diseases.[7] Passive
immunity provides immediate protection, but the body does not develop memory,
therefore the patient is at risk of being infected by the same pathogen later.[8]

Naturally acquired
Maternal passive immunity is a type of naturally acquired passive immunity, and
refers to antibody-mediated immunity conveyed to a fetus by its mother during
pregnancy. Maternal antibodies (MatAb) are passed through the placenta to the
fetus by an FcRn receptor on placental cells. This occurs around the third month
of gestation. IgG is the only antibody isotype that can pass through the placenta.
Passive immunity is also provided through the transfer of IgA antibodies found
in breast milk that are transferred to the gut of the infant, protecting against
bacterial infections, until the newborn can synthesize its antibodies. Colostrum
present in mothers milk is an example of active immunity. [8]

Artificially acquired
Artificially acquired passive immunity is a short-term immunization induced by
the transfer of antibodies, which can be administered in several forms; as human or
animal blood plasma, as pooled human immunoglobulin for intravenous (IVIG) or
intramuscular (IG) use, and in the form of monoclonal antibodies (MAb). Passive
transfer is used prophylactically in the case of immunodeficiencydiseases, such
as hypogammaglobulinemia.[9] It is also used in the treatment of several types of
acute infection, and to treat poisoning.[7] Immunity derived from passive
immunization lasts for only a short period of time, and there is also a potential risk
for hypersensitivity reactions, and serum sickness, especially from gamma
globulin of non-human origin.[8]

The artificial induction of passive immunity has been used for over a century to
treat infectious disease, and before the advent of antibiotics, was often the only
specific treatment for certain infections. Immunoglobulin therapy continued to be a
first line therapy in the treatment of severe respiratory diseases until the 1930s,
even after sulfonamide lot antibiotics were introduced
Active immunity:

The time course of an immune response. Due to the formation of immunological

memory, reinfection at later time points leads to a rapid increase in antibody
production and effector T cell activity. These later infections can be mild or even
unapparent.

 If host itself produces antibodies, it is called active immunity.

 It is of two types; artificial active immunity and natural active immunity.

 Artificial active immunity: Immunity provided by vaccination.

 Natural active immunity: immunity provided by natural infection.

When B cells and T cells are activated by a pathogen, memory B-cells and T- cells
develop, and the primary immune response results. Throughout the lifetime of an
animal, these memory cells will "remember" each specific pathogen encountered,
and can mount a strong secondary response if the pathogen is detected again.
The primary and secondary responses were first described in 1921 by English
immunologist Alexander Glenny[10] although the mechanism involved was not
discovered until later.This type of immunity is both active and adaptive because
the body's immune system prepares itself for future challenges. Active immunity
often involves both the cell-mediated and humoral aspects of immunity as well as
input from the innate immune system.

Naturally acquired

Naturally acquired active immunity occurs when a person is exposed to a live

pathogen and develops a primary immune response, which leads to immunological
memory.[7] This type of immunity is "natural" because deliberate exposure does not
induce it. Many disorders of immune system function can affect the formation of
active immunity such as immunodeficiency (both acquired and congenital forms)
and immunosuppression.

Artificially acquired[edit]

Artificially acquired active immunity can be induced by a vaccine, a substance that

contains antigen. A vaccine stimulates a primary response against the antigen
without causing symptoms of the disease.[7] Richard Dunning coined the term
vaccination, a colleague of Edward Jenner, and adapted by Louis Pasteur for his
pioneering work in vaccination. The method Pasteur used entailed treating the
infectious agents for those diseases, so they lost the ability to cause serious disease.
Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery,
which Pasteur's work built upon.
Poster from before the 1979 eradication of smallpox, promoting vaccination.

In 1807, Bavaria became the first group to require that their military recruits be
vaccinated against smallpox, as the spread of smallpox was linked to
combat.[11] Subsequently, the practice of vaccination would increase with the
spread of war.
There are four types of traditional vaccines:

 Inactivated vaccines are composed of micro-organisms that have been killed

with chemicals and/or heat and are no longer infectious. Examples are vaccines
against flu, cholera, plague, and hepatitis A. Most vaccines of this type are
likely to require booster shots.
 Live, attenuated vaccines are composed of micro-organisms that have been
cultivated under conditions which disable their ability to induce disease. These
responses are more durable and do not generally require booster shots.
Examples include yellow fever, measles, rubella, and mumps.
 Toxoids are inactivated toxic compounds from micro-organisms in cases where
these (rather than the micro-organism itself) cause illness, used prior to an
encounter with the toxin of the micro-organism. Examples of toxoid-based
vaccines include tetanus and diphtheria.
 Subunit vaccines are composed of small fragments of disease-causing
organisms. A characteristic example is the subunit vaccine against Hepatitis B
virus.

Most vaccines are given by hypodermic or intramuscular injection as they are not
absorbed reliably through the gut. Live attenuated polio and
some typhoid and cholera vaccines are given orally in order to produce immunity
based in the bowel.
 Immune Response:
The immune response involves primary immune response and secondary
immune response.
(a) The primary immune response:
 After an initial contact with an antigen, no antibodies are present for a period
of several days. Then, a slow rise in the antibody titer o(arbitrary units)
occurs, first IgM and then IgG followed by a gradual decline in antibody
titer. This is called the primary immune response.
 (b) The secondary immune response:
 Memory cells may remain in the body for decades. Every new encounter
with the same antigen results in a rapid proliferation of memory cells. This is
also called “booster response”. The antibody titer after subsequent
encounters is far greater than during a primary response and consists mainly
of IgG antibodies. This accelerated, more intense response is called the

 secondary immune response. Antibodies produced during a secondary

response have an even higher affinity for the antigen.

 A person who had been suffering from diseases like measles, small pox or
chicken pox becomes immune to subsequent attacks of these diseases. It
includes spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and
appendix.

 The increased power and duration of the secondary immune response

explain why immunization (method of providing immunity artificially, it is
called vaccination) is usually accomplished by injecting antigen in multiple
doses.
 Summary Of Immunity -
 the study of immunity help to understand immune power of the body and its
function. immunity is the protection power of body its protect from invasion
of pathogen it is resistances power of body. immunity mostly divided into
two type natural and artificial. the natural immunity is the birth immunity it
is transfer from one generation to other generation, natural immunity
made before birth natural immunity is also individual immunity its come
from birth. natural immunity divided into to types specific and non specific.
the specific immunity generated in individual to any infection such as small
pox and non specific immunity of individual such as skin,mucus,digestive
system,urinary system,respiratory system etc they are help to protection
from infection.artificial immunity it is ready made immunity
its acquired after birth such as antibody transfer through mother milk and
other example is vaccination or immunization.
Bibliography

 Onlinebiologynotes
 Biologydiscussion
 nursinglectureclass.blogspot.in