12.immune system

Immune system
Watch the video for more explanation  https://oke.io/Sv4JL7LC

INTRODUCTION
• Immunity is concerned with the recognition
and disposal of foreign or ‘non-self’ materials
that enter the body , usually in the form of
life-threatening infectious micro-organisms
but sometimes, unfortunately in the shape of
a life saving kidney graft.

INTRODUCTION....Contd
• Immunology is the study of the organs, cells, and
molecules responsible for the recognition and
disposal[immune system], how they interact, the
consequences weather desirable or otherwise of their
activities and ways in which they can be advantageously
increased or reduced.
• Immune system is the body’s natural defence system that
helps fight infections.
• Resistance to infection may be natural/innate or
acquired.

Immune system.....
HOW DOES IT WQRK?

Immune system cntd.....
• In order to be effective, the immune system needs to be
able to identify which particles are foreign and which are a
part of the body (a mechanism known as recognition)
hence the need to know the terms;
– Self; refers to particles, such as proteins and other molecules,
that are a part, or made by ones body. they can be found
circulating in the blood or attached to different tissues. Not
targeted or destroyed by the immune system.
– Tolerance; the non reactivity of the immune system to self
particles.
– Watch the video for more explanation 
https://oke.io/Sv4JL7LC

Immune system cntd....1
– Non self; refers to particles that are not made by the
body, and are recognised as potentially harmful. These
are often called foreign bodies. They can be bacteria,
viruses, parasites, pollens, dust and toxic chemicals.
– Antigens; substances capable, under appropriate
condition, of inducing the formation of antibodies and
reacting specifically with the antibodies produced.
They are divided into hetero-antigens and auto-
antigens.
– Note; these antigenic molecules may have several
antigenic determinants, called epitopes, and each
epitope can bind with specific antibody.

Immune system cntd.....2
– Hetero-antigens; foreign antigens originating from
outside the body. examples include parts of or
substances produced by non self particles.
– Auto-antigen; antigens that originate from the
body. an anomaly that occurs in persons with
autoimmune disorders e.g. Addison's disease,
myasthenia gravis

– Antibodies; proteins produced by the immune
system in response to the presence of antigen.
– Immunological memory refers to the ability of the
immune system to respond more rapidly and
effectively to a pathogen that has been previously
encountered.

– Vaccination; a method of stimulating the adaptive
immune response and generating memory and
acquired resistance without suffering the full
effect of the disease
– Hypersensitivity; is a set of undesirable reactions
produced by the normal immune system. occurs
as a result of re-exposure to a previous stimulus.
e.g. allergy

COMPONENTS OF THE IMMUNE
SYSTEM

Components of the immune system
• The immune system is made up of antibodies,
white blood cells and other chemicals and
proteins that attack and destroy substances
such as bacteria and viruses that they
recognise as foreign and different from the
body’s normal healthy tissue. they are;
– The lymphatic system made up of the lymph
nodes and vessels.

Components of the immune
system....Cntd
– The bone marrow made up of the red marrow
which produces RBCs AND WBCs as well as
platelets. And the yellow marrow.
– spleen: filters the blood by removing old or
damaged blood cells and platelets and helps the
immune system by destroying bacteria and other
foreign substances .
– The tonsils and thymus, which make the
antibodies.

Innate/natural immunity
• It is the first line of defence
• It is made up of defences against infections
that can be activated immediately once a
pathogen attacks.
• Watch the video for more explanation 

Innate/natural immunity....1
• It is always general or non specific, meaning
anything that is identified as foreign or non-
self is a target for the innate immunity.
• It is essentially made up of barriers that aim to
keep viruses, bacteria, parasites and other
foreign particles out of the body or limit their
ability to spread or move throughout the
body.

• It includes
– Physical barriers; such as skin, G.I tracts,
respiratory tract, naso-pharynx, cilia.
– Defence mechanism; such as secretions, saliva,
lysozyme( found in tears and sweat), gastric acid,
mucous, bile, lactic acid (found in vaginal and
urinary tract).

• General immune responses; such as inflammation
responses, complements, non specific cellular
responses. These inflammatory responses actively
bring cells to the site of an infection by increasing
blood flow to the area while complement marks
pathogens for destructions by making holes in the
cell membrane of the pathogen.

Cells of the innate immune system
• Phagocytes or
phagocytic cells ;
circulate throughout
the body, looking for
potential threats like
bacteria and viruses to
engulf and destroy.
• Watch the video for
more explanation 

Cells of the innate immune
system....cntd
• Macrophages; they are efficient phagocytic
cells that leave the circulatory system by
moving across the walls of capillary vessels.
They can also release cytokines in order to
signal and recruit other cells to an area with
pathogens.

Cells of the innate immune system....
• Mast cells; they are found
in mucous membrane
and connective
membrane and are
important. They are
involved in inflammatory
responses.
• When activated, they
release cytokines and
granules that contain
chemical molecules
create inflammatory
cascade.

• Neutrophils; are phagocytic cells that are also classified
as granulocytes as they contain granules in their
cytoplasm which are toxic to bacteria and fungi and
prevent them from proliferating or die on contact.
• Eosinophils; granulocytes, secreate a range of highly
toxic proteins and free radicals that kill bacteria and
parasites. Use of these toxicproteins and free radicals
also cause tissue damage during allergic reactions, thus
their activation and toxin release is highly regulated to
prevent unnecessary tissue damage.

• Basophils; granulocytes that attack
multicellular parasites.
• Natural killer cells: do not attack pathogens
directly, rather they destroy infected host cells
in order to stop the spread of an infection.
Infected or compromised host cells can signal
natural killer cells for destruction.

Cells of the innate immune system...
• Dendritic cells: Dendritic cells are antigen-presenting
cells that are located in tissues, and can contact
external environments through the skin, the inner
mucosal lining of the nose, lungs, stomach, and
intestines. Since dendritic cells are located in tissues
that are common points for initial infection, they can
identify threats and act as messengers for the rest of
the immune system by antigen presentation. Dendritic
cells also act as bridge between the innate immune
system and the adaptive immune system.

Cells of the innate immunity...

Adaptive immunity.
• Why do I recover faster
than previous times
following courses of
common cold, flu and
some small infections?

ADAPTIVE/ACQUIRED IMMUNITY
• Uses specific antigens to strategically mount an
immune response
• Specificity; term used to denote the production
of immune response more or less specific for the
stimulus.
• It is based on the special properties of
lymphocytes(T & B) which can respond selectively
to thousands of different non-self materials, or
antigens.

ADAPTIVE/ACQUIRED
IMMUNITY...Cntd
• This leads to specific memory and a
permanently altered pattern of response.
• Slower to respond to threats and infections
than the innate immunity.

CELLS OF ADAPTIVE IMMUNITY
• Relies on fewer types of cells to carry out its
tasks: the B and T cells.
• Both are lymphocytes that are derived from
specific types of stem cells, called multipotent
hematopoietic stem cells, in the bone marrow,
they need to mature and become activated.

CELLS OF ADAPTIVE IMMUNITY
• B lymphocytes; produced in the bone marrow.
– Migrates to the lymphatic system where it matures on contact
with antigens that fits or matches its membrane bound antibody
and divides into two types.
– Memory B cell; express the same membrane bound antibody
that is produced by the ‘parent’ B cell.
– Plasma/Effector B cell; also produce the same antibody as the
parent B cell but in this case, it isn't membrane bound rather
its secreted and have the ability to identify free pathogens that
are circulating in the body.

CELLS OF ADAPTIVE IMMUNITY....cntd
• T Lymphocyte
– Formed in the bone marrow as T progenitor cell
from where it migrates to the thymus for
maturation and becomes T cells.
– While in the thymus, the developing T cells start
to express ; T cell receptors
CD4 or CD8 receptors. meaning some will
express CD4 and some CD8 receptors.

– T cell receptors only recognise antigens that are
bound to certain receptor molecules, called Major
Histocompatibility Complex (MHC1) and MHC2. these
MHC molecules are membrane-bound surface
receptors on antigen presenting cells, like dendritic
cells and macrophages.
– T cell receptors undergo a process called
rearrangement which leads to either positive or
negative selection.
CELLS OF ADAPTIVE IMMUNITY....1

– 3 types of T cells is the result of selection and they
include.
• Helper T cells which expresses CD4, and helps with the
activation of cyto-toxic T cells and other immune cells.
• Cyto-toxic T cells which expresses CD8 and are responsible
for removing pathogens and infected host cells.
• T regulatory cells which expresses CD4 and CD25. Helps to
differentiate between self and non-self molecules and hence
reduce the risk of autoimmune diseases.

• Antigen presenting cells.
– These are cells on which MHC molecules are
bound.
– They form the link between innate and acquired
immunity.
– Examples are macrophages and dendritic cells.

Adaptive immunity (cntd)
• Adaptive immunity provides two types of
immunity which as earlier explained depend on
the B and T lymphocytes. They are;
– Humoural immunity
– Cell mediated immunity

HUMORAL IMMUNITY
• Involves B cells that recognize antigens or
pathogens that are circulating in the lymph or
blood(humor). The response follows this chain of
events.
– Antigens bind to B cells
– In most cases, interleukins or helper t cells co
stimulate the B cells.
– B cells proliferate and produce plasma cells. They
release antibodies which circulate through the body
and bind antigens.
– B cells produce memory cells which produce future
immunity.

CELL MEDIATED IMMUNITY
• Involves mostly T cells and respond to any
cells that displays aberrant MHC markers,
including cells invaded by pathogens, tumour
cells, or transplanted cells. Follows the
following chain of events.
– Self cells or APCs displaying antigens bind to T
cells.
– Interleukins secreted by APCs or helper T cells co
stimulate activation of T cells.

– If MHC-1 and endogenous antigens are displayed on the
plasma membrane, T cells proliferate producing cytotoxic T
cells. Cytotoxic T cells displaying the antigens.
– If MHC-2 and exogenous antigens are displayed on the
plasma membrane, T Cells proliferate producing helper T
cells.
– Helper T cells release interleukins(and other
cytokines),which stimulate B cells to produce antibodies to
the antigens and stimulate non specific agents(NK and
macrophages)to destroy the antigens.
CELL MEDIATED IMMUNITY...Cntd

INTERACTIONS BETWEEN NATURAL
AND ADAPTIVE IMMUNITY
• Antibody; serum globulins with a wide range
of specificity for different antigens. Although
they bind to neutralise bacterial toxins
directly, they exert most of their effects by
binding to the surfaces of bacteria, viruses, or
other parasites and thus increasing their
adherence to, and phagocytosis by myeloid
cells. This phenomenon is known as
opsonization.

AND ADAPTIVE IMMUNITY
• Complement; it is often activated by antibody to
microbial surfaces. However binding of a
complement to antigen can also greatly increase
its ability to activate a strong and lasting B cell
response.
• Presentation of antigen to T and B cells is
necessary for most of adaptive responses. this is
made possible by the APCs such as macrophages
and dendritic cells(cells of innate immunity).

AND ADAPTIVE IMMUNITY....Cntd
• Help by T cells is required for many branches
of the immune system. it is required for the
secretion of most antibodies by B cells and for
activating macrophages to stimulate cellular
immunity.

INTERACTION BETWEEN INNATE AND
ACQUIRED IMMUNITY.

SUMMARY
INNATE
INNATE
• Response time is fast; minutes
or hours
• Non specific or only specific for
molecules and molecular
patterns associated with general
pathogens or foreign particles
• Major cell types; NK cells,
macrophages, neutrophils,
basophils, eosinophils, dendritic
cells
• No immunological memory
ADAPTIVE
ADAPTIVE
• Slow; takes days
• Highly specific. Can
differentiate between
pathogen and non pathogen
structures.
• Major cell types; T cells, B cell
and other antigen presenting
cell.
• Possess immunological
memory which leads to faster
response to recurrent or
subsequent infections.

Innate.
• Key component;
antimicrobial peptides and
proteins, such as toxic
granules.
• Diversity and customization;
limited as receptors used
are standard and only
recognise antigen patterns.
No new receptors are made
to adapt to immune
responses.
Adaptive.
• Antibodies
• Highly diverse; can be
customized by genetic
recombination to recognize
epitopes and antigenic
determinants.
SUMMARY...Cntd

Undesirable effects of immune system
• Hypersensitivity reaction
• Auto-immune diseases
• Transplant rejection.

The concept of autoimmunity and
autoimmune diseases.
• Autoimmunity signifies an immune response
against self and may be assymptomatic as
opposed to autoimmune disease which occurs
when autoimmunity leads to an inflammatory
response, resulting in tissue injury.
• That is, an autoimmune response doesn’t
necessarily imply the existence of autoimmune
disease.

Autoimmune diseases
• Autoimmune disease may be mediated primarily
by
– T cells as in multiple sclerosis.
– B cells that produce auto-antibodies that bind to self
antigens (proteins, nucleic acids, or other molecules
from ones body, also known as auto-antigens) and can
damage cells either by binding directly to cell surface
antigens or by formation of autoimmune complexes.

Autoimmune diseases
• Autoimmune diseases could also be;
– System specific e.g.
• Systemic lupus erythematosus (joints, skin, nervous system,
kidneys, blood cells, heart, lungs).
• Rheumatoid athritis (joints, blood vessels, lungs).
– Organ specific such as in
• Graves disease (thyroid)
• Hashimoto thyroiditis (thyroid)
• Myasthenia gravis (nervous system)

Transplant rejection.
• example of these can be seen in
– ABO blood typing incompatibility: occurs when
recipients lacking a certain blood type produce IgM
antibodies against that antigen and cause subsequent
activation of complement and lysis of transfused
incompatible red blood cells.
– Solid organ allograft rejection.

12.immune system

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