Organization of Immune System (2)

8/6/2019 Organization of Immune System (2)

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Learning OutcomesLearning Outcomes

At the end of the lecture, student should

be able to:

Explain the function of immune system

Classified the types of immune system.


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The Immune SystemThe Immune System

Types of Immune Response:Types of Immune Response:

Innate ImmunityInnate Immunity Acquired/ adaptive Immunity :Acquired/ adaptive Immunity :

a) Cella) Cell--Mediated ResponseMediated Response

b)b) HumoralHumoral ResponseResponse

Lymphatic TissuesLymphatic Tissues


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D

ual nature of the ImmuneSystemThe architecture of the immune system is multiThe architecture of the immune system is multi--layered,layered,with defenses on several levels.with defenses on several levels.

Several barriers (external to internal /simple toSeveral barriers (external to internal /simple to

complex) provided at many levels of infection and thecomplex) provided at many levels of infection and theimmune system has a series of dual natures:immune system has a series of dual natures:

1. Self/ non-self recognition

2. Natural / adaptive

3. Cell mediated / humoral4. Passive / active


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Characteristics of the immuneresponse

1. Specificity:: the ability to distinguish betweenthe ability to distinguish between

antigensantigens

2. Adaptiveness: the ability to respond to previouslythe ability to respond to previouslyunseen molecules.unseen molecules.

3. Recognition of self and non-self : the ability tothe ability to

recognize and respond to molecules that arerecognize and respond to molecules that are

foreign or nonforeign or non--self and the molecules that areself and the molecules that are

self.self.

4. Memory:: the ability to recall previous contact with athe ability to recall previous contact with a

foreign molecule and respond to it in a learnedforeign molecule and respond to it in a learned

manner.manner.


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Functions of immune systemFunctions of immune system

The immune system like any organization, hasThe immune system like any organization, has

members that perform different functions tomembers that perform different functions to

accomplish a common goal.accomplish a common goal.1.1. Provides defenses against pathogensProvides defenses against pathogens

2.2. Removes dead or worn out cells like RBCsRemoves dead or worn out cells like RBCs

3.3. Identifies and destroys abnormal cancer cellsIdentifies and destroys abnormal cancer cells

4.4. Protects from autoimmune diseasesProtects from autoimmune diseases

5.5. Rejects tissues cells of foreign antigens .Rejects tissues cells of foreign antigens .


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Mechanism of immune responseMechanism of immune response

The immune system specifically recognizes andThe immune system specifically recognizes andselectively eliminates pathogens.selectively eliminates pathogens.

There are two critical steps in the immune response:There are two critical steps in the immune response:

1.1. Detection eventsDetection events2.2. Elimination eventsElimination events

The detection and elimination of pathogens dependThe detection and elimination of pathogens dependupon the chemical bonding between receptors on theupon the chemical bonding between receptors on thesurface of an immune cell andsurface of an immune cell and epitopesepitopes found on thefound on thesurface of a pathogen.surface of a pathogen.

TheThe complementary receptorcomplementary receptor epitopeepitope bindingbinding(( monospecificitymonospecificity) activates a complex system of) activates a complex system ofsignallingsignalling that mediates the immune response.that mediates the immune response.


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Mechanism of immune responseMechanism of immune response

ImmuneImmune recognition phaserecognition phase is critical in theis critical in thenormal functioning of the system.normal functioning of the system.

This is accomplished by three sets of antigenThis is accomplished by three sets of antigenbinding molecules :binding molecules :

1. T- cell antigen receptors (TCR)

2. Class I and class II molecules of the MHC

3. B-cell antigen receptor (BCR,

immunoglobulin). TheThe effectoreffector phasephase is mediated by a variety ofis mediated by a variety of

cells and soluble factors.cells and soluble factors.


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Lymphatic vessels are responsible for flow of lymph withinthe lymphoid system

Plasma constantly leaks out of capillaries to deliveroxygen and nutrients to cells of the surrounding tissue.

Once in the tissue, the plasma is now called tissue fluid . While most of this tissue fluid re-enters capillaries and is

returned directly to the bloodstream, some fluid enterslymph vessels as lymph .

LYMPH- flows from the intercellular tissue spaces intolymphatic capillaries and then into a series of larger

collecting vessels called lymphatic vessels. Lymphaticvessels converge into the thoracic duct, which returns thefluid to the circulatory system by dumping into the leftsubclavian vein.


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Thoracicduct

Overview of blood and lymph system and howOverview of blood and lymph system and how

leukocytes travel from one system to anotherleukocytes travel from one system to another

Site of exchange between the

blood and lymph systems

Lymph carrying antibodiesand immune cells collect inthoracic duct where thelymph empties back into theblood circulatory system


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Immune cells travel back and forth fromImmune cells travel back and forth fromthe blood and lymph circulatory systemsthe blood and lymph circulatory systems

and interact with extraand interact with extra--vascular tissues invascular tissues in

the processthe process----extravasationextravasation

muscle


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Functions of lymphatic organsFunctions of lymphatic organs

1. Generate immuno-competantlymphocytes.

2. Concentrate antigens into lymphoidorgans.

3. Circulate lymphocytes throughlymphoid organs, exposing antigen to a

variety of lymphocytes.4. Deliver antibodies and effector T cells to

the blood and tissues.


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Lines of Defense

1st Line1st Line barriers at portals of entrybarriers at portals of entry primarily inborn and nonspecificprimarily inborn and nonspecific

physical barriers which include the skin, urine,physical barriers which include the skin, urine,tears,tears, ciliaryciliary elevator, mucosal membrane, etcelevator, mucosal membrane, etc..

come into play when barriers are breachedcome into play when barriers are breached

primarily inborn and nonspecificprimarily inborn and nonspecific

are the macrophage system, complement,are the macrophage system, complement,fever, interferon and inflammation.fever, interferon and inflammation.


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2nd Line2nd Line antibodies andantibodies and cytotoxiccytotoxic cellscells

provides longprovides long--term immunity afterterm immunity afterencountersencounters

primarily acquired and specificprimarily acquired and specific

consists of B cells (consists of B cells (humoralhumoral), and T cells), and T cells(cell(cell--mediated).mediated).


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Physical and Chemical DefensesPhysical and Chemical Defenses


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continuecontinue

SkinSkin provides an almost impenetrableprovides an almost impenetrablebiological barrier.biological barrier.

LysozymeLysozyme is an enzyme found in tears andis an enzyme found in tears andsaliva thatsaliva that can break down foreign agents .can break down foreign agents .

The clotting of blood near open woundsThe clotting of blood near open woundsprevents an open space for antigens.prevents an open space for antigens.

Mucus and cilia found in the nose andMucus and cilia found in the nose andthroat can catch foreign agents thenthroat can catch foreign agents then

sweep them outside viasweep them outside via coughing, sneezingcoughing, sneezingand vomiting.and vomiting.


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Second Line of DefenseSecond Line of Defense--22

Second lines of defense deal with antigens that

have bypassed the first lines of defense.

Interferons are a family of proteins that are

released by a cell that is under attack by anantigen.

One method of attacking antigens is byphagocytosis , where the contents of the

antigen are broken down by molecules called

phagocytes.


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A second line of defense is thespecific/adaptive immune system which

may take days to respond to a primaryinvasion

The production of antibodies and cell-mediated responses may occur in whichspecific cells recognize foreign pathogens

and destroy them. The response is often more rapid because

of the activation of memory B and T cells. cells of the immune system interact with one

another by a variety of signal molecules. These signals may be proteins such aslymphokines, cytokines and chemokineswhich stimulate cells of the immune system.


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Immune SystemImmune System

Two types of immune systemTwo types of immune system

InnateInnate immune systemimmune system

AdaptiveAdaptive immune systemimmune system


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Main Types of Immunity in ManMain Types of Immunity in Man

Immunity

Innateimmunity

Adaptiveimmunity

Natural Artificial

Passive (maternal)

Active (Infection)

Passive (Serotherapy)

Active (Vaccination)


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Innate ImmunityInnate Immunity responds immediatelyresponds immediately protects the body from all foreignprotects the body from all foreign

substancessubstances

Consists of various types of barrier thatConsists of various types of barrier that

prevent entry of foreign agents such as:prevent entry of foreign agents such as:

a) anatomical barriersa) anatomical barriers

b) physiological barriersb) physiological barriers

c) inflammatory barrier.c) inflammatory barrier. Comprises all defense elements which anComprises all defense elements which an

individual is born with it.individual is born with it.


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A) anatomical barriers:A) anatomical barriers:

-- Block the entry of organismBlock the entry of organism

-- Consist of skin and the mucousConsist of skin and the mucous

-- Entraps foreign microorganism and ciliaEntraps foreign microorganism and cilia

propels microorganism out of the body.propels microorganism out of the body.

-- B) Physiological barriersB) Physiological barriers

-- Factor like body temp, pH, and variousFactor like body temp, pH, and various

body secretions prevent growth ofbody secretions prevent growth ofpathogens.pathogens.


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C) Inflammatory barriersC) Inflammatory barriers

Response occur due to release ofResponse occur due to release ofchemical by the damaged most cells.chemical by the damaged most cells.

Redness, swelling, pain and production ofRedness, swelling, pain and production of

heat is known as inflammatory response.heat is known as inflammatory response. Influx ofInflux of phagocyticphagocytic cell into affectedcell into affected

area to inhibit and destroy the invadingarea to inhibit and destroy the invading

micromicro--organism.organism.


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Acquired immunityAcquired immunity The second level of defense increases in

strength and effectiveness with eachencounter. The foreign agent is recognized in a

specific manner and the immune systemacquires memory towards it.

The first encounter with an antigen is known asthe primary response. Re-encounter with thesame antigen causes a secondary responsethat is more rapid and powerful


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As response produce antibodies to specificinfections

Some features

Memory

Each successive encounter with the samepathogen improve the response

Clonal selection

Select the best and matured immune cells to

defend the organism against infections


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Acquired ImmunityAcquired Immunity

Also known as adaptive or specific

immunity.

Capable of recognizing and selectively

eliminating specific microorganism Supplements the protection provided by

innate immunity.

Require several days to be activated


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It has the following unique features:

1) specificity : ability to distinguishdifference among various foreign

molecules.

2) diversity: recognize a variety of foreignmolecules

3) memory:

4) discrimination between self and non

self molecules.


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Acquired immunity employs two majors

groups of:

a) lymphocytes ( B and T cell)

b) antigen presenting cells

The B and T cells, together generate 2

types of specific immunity:

a) cell mediated immunity ( by T cells)

b) humoral immunity ( by B cells)


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HumoralHumoral immunity (HI)immunity (HI)

It is also called antibody- mediated immunity

B cells produce specialized protein calledantibodies.

These protein is highly specific to specificantigens.

Each antigen has many different antigenicdeterminants, each of which matches a

specific antibody and bind to it. Antibody molecule can be free or may be

bound to a cell membrane.


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Free antibodies have 3 main functions:

1) Agglutination agglutinate particular

matter including bacteria and viruses.

2) Opsonisation opsonise of bacteria to

facilitate their subsequent phagocytesby cell.

3) Neutralization neutralize toxin released

by bacteria.


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Cell Mediated ImmunityCell Mediated Immunity

Responsibility of a subgroup of T-cells calledT-cytotoxic

An activated T-cytotoxic is specific to a

target cells which have been infected. Kill the target cell by variety of mechanism.

Dont secrete antibody but responsible forrecognition of antigen, on contact with

antigen. Responsible for immunity against many

disease


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Whenever T cells and B cells are activated,some become "memory" cells. The next timethat an individual encounters that sameantigen, the immune system is primed todestroy it quickly. This is active immunity.

Long-term active immunity can be naturallyacquired by infection or artificially acquired byvaccines

Short-term passive immunity can betransferred artificially from one individual toanother via antibody-rich serum;


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Active and Passive AcquiredActive and Passive AcquiredImmunityImmunity

Active immunity

Conferred by recovery from infectious disease

Depends on persons own immune system.

May be acquired artificially with vaccines.

Passive immunity

transferred from person to person through transfer of antibodies.

Natural instances include antibodies passing across placentafrom mother to fetus (provides temporary protection) or throughthe milk.

Transferred artificially. E.g. antibody injections for rabies, antirhesus factor, snake venom, botulinun toxin.


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Immunity is a coordinated effort by theImmunity is a coordinated effort by the

bodybody..

It was previously believed that the immune systemfunctioned independently in the body.

Its now known that there are several links between theimmune, nervous and endocrine systems.

Certain immune responses trigger endocrine &/or nervousactivity.

Lymphocytes & macrophages are responsive to signals fromthe nervous system and certain endocrine glands.

Therefore, immunity is the job of the entire body not just onesystem.


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Organization of Immune System (2)

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