Immunity gihs

OUTLINE
 Overview
 Definition
 Types
 Vaccination

Overview of the immune system
 The immune system is a complex system of interacting
cells whose primary purpose is to identify foreign
(“non-self”) substances referred to as antigens.
 The immune system provides protection from
infectious disease by identify most of these microbes
as foreign.

THE LYMPHATIC SYSTEM
 The lymphatic vessels (or lymphatics) are a network of
thin tubes that branch, like blood vessels, into tissues
throughout the body.
 Lymphatic vessels carry lymph, a colorless, watery
fluid originating from interstitial fluid (fluid in the
tissues).
 Along this network of vessels are small organs called
lymph nodes.
 Clusters of lymph nodes are found in the underarms,
groin, neck, chest, and abdomen.

 The lymphatic system, which transports infection-fighting
cells called lymphocytes, is involved in the removal of
foreign matter and cell debris by phagocytes (cells that
engulf) and is part of the body's immune system.
 When the body is fighting an infection, these lymphocytes
multiply rapidly and produce a characteristic swelling of the
lymph nodes
 Lymphatic tissue is also found in other parts of the body,
including the stomach, intestines, and skin. Other parts of
the lymphatic system are the spleen, thymus, tonsils, and
bone marrow.

 The thymus and bone marrow are the primary lymphatic organs.
 Lymphocytes are produced by stem cells in the bone marrow and
then migrate to either the thymus or bone marrow where they
mature.
 T-lymphocytes undergo maturation in the thymus (hence their
name), and B-lymphocytes undergo maturation in the bone
marrow.
 After maturation, both B- and T-lymphocytes circulate in the
lymph and accumulate in secondary lymphoid organs, where they
await recognition of antigens.

Cells and molecules of the
immune system
 Immune responses are mediated by a variety of
cells, and by the soluble molecules that they
secrete. Although the leucocytes are central to
all immune responses, other cells also
participate, by signaling to the lymphocytes
and responding to the cytokines (chemical
messengers) released by T lymphocytes and
macrophages.

SELECTED CELLS AND THEIR
FUNCTIONS
Leukocytes (White Blood Cells)
 B-cells: Lymphocytes normally involved in the production of
antibodies to combat infection.
 They are precursors to plasma cells.
 During infections, individual B-cell clones multiply and are
transformed into plasma cells, which produce large amounts
of antibodies against a particular antigen on a foreign
microbe.
 This transformation occurs through interaction with the
appropriate CD4 T-helper cells.

 T-cells:
 A class of lymphocytes, so called because they are
derived from the thymus and have been through
thymic processing.
 Involved primarily in controlling cell-mediated
immune reactions and in the control of B-cell
development.
 The T-cells coordinate the immune system by
secreting lymphokine hormones (these are cytokines
released by lymphocytes).
 There are 3 fundamentally different types of T-cells :
helper, killer, and suppressor. Each has many
subdivisions. T-cells are also called T lymphocytes.

Phagocytes - Mononuclear phagocytes,
Neutrophils, Eosinophils.
These cells engulf foreign organisms or
particles.
 They form a link between the specific and the
non specific arms of the immune system by
presenting foreign fragments on their surface
to T-cells and B-cells.

A phagocyte is a cell that ingests (and
destroys) foreign matter, such as
microorganisms or debris via a
process known as phagocytosis,
in which these cells ingest and kill
offending cells by cellular digestion.

ANTIGEN
An antigen is a substance that stimulates
an immune response, especially the
production of antibodies.
 Antigens are usually proteins or
polysaccharides (long chains of sugar
molecules that make up the cell wall of
certain bacteria),

 Antigens induce immunity.
 The immune system develops a defence against foreign
antigens.
 This defence is known as the immune response and
usually involves the production of protein molecules,
called antibodies (or immunoglobulins or Ig), and of
specific cells (also known as cell-mediated immunity)
whose purpose is to facilitate the elimination of
foreign substances

Antibody
 An antibody is a protein used by the immune system to
identify and neutralise foreign objects like bacteria
and viruses. Each antibody recognises a specific
antigen unique to its target.

There are five classes of antibody – IgG,
IgA, IgM, IgD and IgE.
These are all structurally slightly different
have a range of functions.
 Each B-cell can produce only one
specific antibody to an antigen, each
antibody is highly specific and will bind
to only one antigen.

 IgA is found primarily in secretions such as breast milk, tears,
saliva and mucosal membranes.
 IgE – evolved to provide protection against certain parasitic
infections however in developed countries it is more
commonly associated with allergic diseases such as asthma
and hayfever.
 IgD – there is little known about this antibody.

 IgG- This class of antibody is the most important
class of immunoglobulin in secondary immune
responses. IgG crosses the placenta, conferring
protection to the new born and is able to activate the
complement system through the classical pathway.
 IgM is the predominant antibody in the primary
immune responses. It can also activate the classical
pathway complement.

NON SPECIFIC DEFENCES
In the first instance the exterior defenses of the
body present an effective barrier to most
organisms and very few infectious agents can
penetrate the intact skin.
There are also a variety of biochemical and
physical barriers.
The body also tolerates a number of
commensal organisms, which compete
effectively with many potential pathogens.

Examples of non-specific immunity:
Skin - a great physical barrier, like a
waterproof wall.
Mucus – sticky, germs get stuck in it, it also
has antibody in it.
Cilia – hairs that pass debris up throat and out
to the nostrils.
Lysosyme - an enzyme present in tears that
breaks down bacteria.
Phagocytes – various cells that scavenge up
and engulf cell debris.

 Commensal bacteria- Non-harmful bacteria on skin and
gut that leave little or no room for harmful bacteria to
attach, and limited nutrients for them to grow.
 Acid - in stomach and urine, make it hard for any germs
to survive.
 Fever – elevates the temperature making it difficult for
infectious agents to survive.
 Non-specific defences are present in all normal
individuals. The non-specific system alerts the specific
arm of the immune system to infection.

Non-specific defenses are present in all
normal individuals. The non-specific
system alerts the specific arm of the
immune system to infection.

DEFINITION OF IMMUNITY
immunity is the state of having sufficient
biological defences to avoid infection,
disease, or other unwanted biological
invasion.
 It is the capability of the body to resist
harmful microbes from entering it.

TYPES OF IMMUNITY
 Active and passive immunity
 There are two basic mechanisms for acquiring
immunity - active and passive.
 Active immunity is protection that is produced by the
person’s own immune system. This type of immunity is
usually permanent.

Active immunity is stimulation of the
immune system to produce antigen-specific
humoral (antibody) and cellular immunity.
active immunity usually lasts for many
years, often for a lifetime.
One way to acquire active immunity is to
have the natural disease.
In general, once persons recover from an
infectious disease, they will be immune to
those diseases for the rest of their lives.

Another way to produce active
immunity is by vaccination.

 Passive immunity is protection by products produced
by an animal or human, and transferred to another
human, usually by injection.
 Passive immunity often provides effective
protection, but this protection disappears with time,
usually a few weeks or months.

 The most common form of passive immunity is that
which an infant receives from its mother.
 Antibodies are transported across the placenta during
the last 1-2 months of pregnancy.
 These antibodies will protect the infant from certain
diseases for up to a year.
 Protection is better against some diseases (e.g.,
measles, rubella, tetanus) than others (e.g., polio,
pertussis).

TYPES OF IMMUNE RESPONSE.
 Any immune response involves, firstly, recognition of the
pathogen or other foreign material, and secondly, a reaction
to eliminate it.
Broadly, the different types of immune response fall into
two categories;
innate (non adaptive)
adaptive immune responses.
.

adaptive immune response is highly
specific for a particular pathogen.
Moreover, innate response does not alter
on repeated exposure to a given infectious
agent, the adaptive response improves
with each successive encounter.

 the adaptive immune system ‘remembers’
the infection agent and can prevent it from
causing disease later.
For example diseases such as measles and
diphtheria induce adaptive immunity which
generates lifelong immunity following
infection.

Immunization, or immunization, is
the process by which an individual's
immune system becomes fortified
against an agent (known as the
immunogen).

TYPES
 Active immunization can occur naturally when a person comes in
contact with, for example, a microbe.
 If the person has not yet come into contact with the microbe and
has no pre-made antibodies for defense, as in passive
immunization, the person becomes immunized.
 The immune system will eventually create antibodies and other
defenses against the microbe.
 The next time, the immune response against this microbe can be
very efficient; this is the case in many of the childhood infections
that a person only contracts once, but then is immune.

 Artificial active immunization is where the
microbe, or parts of it, are injected into the person
before they are able to take it in naturally. If
whole microbes are used, they are pre-treated.

 Passive immunization is where pre-synthesized
elements of the immune system are transferred to
a person so that the body does not need to produce
these elements itself. Currently, antibodies can be
used for passive immunization. This method of
immunization begins to work very quickly, but it
is short lasting, because the antibodies are
naturally broken down, and if there are no B cells
to produce more antibodies, they will disappear.

Vaccination
Vaccination is the administration of
antigenic material (a vaccine) to
stimulate an individual's immune
system to develop adaptive immunity
to a pathogen.

Artificial passive immunization is
normally administered by injection and
is used if there has been a recent
outbreak of a particular disease or as an
emergency treatment for toxicity, as in
for tetanus

Immunity gihs

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Immunity gihs