Immune system

Functions of immune system

Protect against infection by microbes.

Isolate or remove nonmicrobial foreign substances.

Destroy cancer cells that arise in the body.

Body Defense System

Non- specific Specific

Passive Active Humoral Cell-mediated

~Mechanical ~ Phagocytosis Immune Immune

barrier Response Response

~Chemical ~ Inflammation (HIR) (CMIR)

barrier

~Blood clots

Body Defense System

Non-specific mechanism

Specific mechanism

Non- specific mechanism

Non-specific mechanism~ do not depend on previous exposure~ do not selectively protect against foreign substan

cea) Passive mechanismb) Active mechanism

Passive mechanism

Mechanical skin & epithelium, ciliated epithelium & mucus

Chemical barrier acid in gastric juice, tears, sebaceous secretion, nasal secretions & saliva, acidic secretion in vagina

Blood clots blood clots prevent further blood loss & entry of pathogenic micro- organisms

Active mechanism

Phagocytosis

~ invading micro-organisms are engulfed by phagocytes

Phagocytosis I

Chemicals released by bacterium are detected by neutrophil

Plasma proteins become attached to bacterium aid identification by neutrophil & adherence of bacterium to neutrophil

Neutrophil moves towards bacterium

Phagocytosis II

Phagosome formed by pseudopodia

Phagocytosis III

Lysosome fuses with phagosome and releases hydrolytic enzymes

Digestion of bacterial call and absorption of products into neutrophil

Phagocytes

amoeboid cells attracted to damaged

area

stimulus for migration chemical liberated by the ruptured blood cells & tissues

found in liver, spleen & lymph nodes

engulf toxic foreign particles localize infection

Inflammation

The body’s response to injury. It involves pain, heat, redness, swelling and loss of function of the affected part.

Active mechanism - Inflammation

Bacteria invade the body

vasodilatation of affected

region

blood supply

reddening, swelling, temp. , pain

Biological significance of inflammation

enables neutrophils migrate to the destroyed area & engulf invaders.

localizes the invading pathogens

plasma protein i.e. fibrinogen blood clot

excess tissue fluid dilute & negate potential toxic irritants

Specific defense mechanism

It depends upon, prior exposure to the specific foreign substances, recognition of it upon subsequent exposure, and the reaction to it.

Terminologies

Antigen ~ foreign body to the host

Antibody ~ blood protein in response to its corresponding antigen;

~circulates in blood to attack

antigen & render it’s harmless.

Specific defense mechanism

Toxoid ~ non- toxic protein toxin, useful

in vaccines

Endotoxin ~ toxic substance produced by bacteria, stay in cell wall

Antitoxin ~ antibody counteracting toxin produced by specific antigen

Lymphocytes ~ a variety of white blood cells

Types of lymphocytes

T- lymphocytes (T- cells)

~ circulate permanently in the blood once produced,

~ colonize in lymph nodes

~ for cell- mediated immune response

~ do not synthesize antibody

Lymphocytes

B- lymphocytes (B-cells)

~ circulate between blood stream & lymphoid organs

~ less than T- cells

~ for humoral immune response

~ able to synthesize antibodies

T & B cells

B cells for humoral immune r

esponse (HIR) thymus independent with finger- like projec

tion on surface synthesize antibodies

when stimulated by antigens

T cells for cell- mediated

immune response (CMIR)

thymus dependent smooth cell surface do not synthesize

antibody

Humoral immune response (HIR)

by B cells

also called antibody- mediated immunityClonal selection B cell proliferation plasma cells & B memory differentiation cells

Humoral Immune Response (HIR)

Antibody

Protein in nature Synthesized by plasma

cells once stimulated by antigen

Ig :2 identical heavy chains (H chain ) + 2 identical light chain (L chain)

A family of proteins with variation in antigen- binding capacities

Humoral immune response

B cells for self proteins will be destroyed during fetal life.

Antigen do not provide information to

plasma cells but select those which can tailor make the specific antibodies.

The unique DNA base sequence in lymphocytes determine the specificity of antibody.

Action of antibodies

Lysis of cell membrane

Agglutination

Stimulation of phagocytosis

Neutralization of toxins

Secondary response of HIR

Memory cells activate body response to second infection of the antigen

Enables prompt & vigorous response in second encounter

short latent period

higher production of antibodies

high specificity

larger population of memory cells

Cell- mediated immune response (CMIR)

by T cells

do not possess antibodies

thymosin promotes T cell maturation

CMIR

HIR vs CMIR

HIRHIR

Time coursePrimary response: 4-5

days

Secondary response: 1-2 days

VenueB cell : lymphoid tissues

e.g. lymph nodes, liver

CMIRCMIR

Time course1 - 2 days

VenueT cell: circulating aroun

d

Importance of HIR

Antibodies ~ act against bacteria, viruses & toxic matters.

Memory cells~ prevent disease.Immunoglobulins ~ replacement therapy in h

umoral- antibody- immunodeficiency diseases.

Serum from horse~ therapy of tetanus, snake bites, rabies etc.

immunoglobulins ~ prevention of graft rejection

Importance of CMIR

Resist infection.Induces unwanted immune response, graft

s or transplants.Destroys tumour.Fast in action to combat the invading path

ogens.Failure/ deficiency of CMIR AIDSAIDS

Specific vs non- specific defence system

SpecificSpecific foreign body: act on

specific substances B & T memory cell

develop secondary response immunity can be

established

Non- specificNon- specific eliminate all foreign

substances non- selectively

no memory cell no secondary

response fight against invading

substances in a fast fashion

Both fight against invading foreign bodies

ImmunityImmunity

Passive Active

Passive immunity in infants Naturally induced

~ antibodies from mother ~ natural encounter

fetus long duration

Artificial passive immunity Artificially induced

~ injection with ~ immunization

immunoglobulin long duration

short duration

Characteristics of active immunity

Antigens are recognized by Lymphocytes first before activating the cells.

Specific antigen elicit the specific antibodies production.

Memory cells can be established.

Naturally acquired immunity

A result of contact to diseases or vaccination.

Achieved injecting small amount of antigen (vaccine) into the body of an individual.

The small dose of antigen is safe.The individual does not contact the diseas

e, but is stimulated to form abtibodies against the antigen.

Booster injection is needed sometimes.

Vaccination

Small dose of antigen is injected to the individual.

either killed or attenuated

~ not contact with disease

~ stimulated to manufacture antibodies

Booster injection quicker production of antibody & long lasting immunity.

Types of vaccine Toxoids e.g. tetanus

~ a preparation of the poisonous material that is produced by dangerous infective organisms.

Killed organisms e.g. dead influenza viruses

Attenuated organisms e.g. TB, measles, poliomyelitis

~ modified but living organisms

Infective agents of a related disease e.g. smallpox

Duration of protection

Smallpox & polio vaccines long lasting, complete protection

BCG fairly long lasting, but not complete protection

TAB typhoid rather temporary & partial protection

Vaccines for special group

Sex groupSex group

Young girls : German measles

Age groupAge group

Young children : Polio, smallpox, measles, cough

OccupationOccupation

Medical workers: Hepatitis B

Sewage workers, field workers: Plague

Traveller

Pros & cons of vaccination

ProsPros

Establishes active immunity against specific diseases

ConsCons

Induces hypersensitivity in some people

Unwanted immune responses

Transfusion reaction Rejection of tissue transplantation

Blood transfusion

If a patient receives blood that is incompatible, a type of unwanted immune response occurs.

Agglutinogens( act as antigens) exist on donor’s RBC membrane.

Incompatible agglutinated donor’s cell

Rejection of tissue transplantationTransplantation ~ replacement of diseased tissues

or organs by healthy ones

Foreign tissue acts as an antigen once inserted into recipient stimulates immune response in the recipient

Rejection of transplanted tissueGraft

CMIR of the host

Proliferation of killer cells

Enhanced phagocytosis

Vascularisation between grafts & the host

REJECTION

Methods to avoid/ minimize graft rejectionTissue matching

~ graft between genetically identical individuals are not rejected.

Immunosuppressive drugs

~ any drug inhibiting mitosis suppresses the response. More prone to cancer

X- irradiation

~ X -irradiation inhibits blood cell production

slow down rejection

Drugs used to treat infectious diseases

For example: Antibiotics Sulphonamides

Antibiotics ~ Organic compounds produced by micro-

organisms.

~ Able to kill or inhibit the activities of other micro- organisms.

Action Action Inhibit cell wall formation

Destroy the selective permeability of cell membrane

Interfere protein synthesis

Inhibit nucleic acid metabolism

Mechanisms of antibiotic resistance

Inactivation of the antibiotics Absence of sensitive structures to antibiotics Presence of barrier to protect the cell Develop alternate metabolic pathway

Avoid antibiotics resistance

Avoid overuse & indiscriminate use Use correct dosage of proper antibiotics Use different antibiotics once

micro-organism shows resistance Use combination of antibiotics

Non- medical use of antibiotics

Growth stimulation

~ poultry & livestock Food preservation

~ preserve fresh meat Controlling plant

diseases

Sulphonamides

~ A group of chemical disturbing the metabolism of folic acid in bacteria

Normal:

Para-aminobenzoic acid Folic acid Normal growth of bacteriaNormal growth of bacteria Presence of Sulphonamides:

Sulpha drug no folic acid produced Bacteria will die Bacteria will die

Problems of drug therapy

Induce the development of drug resistant strains of micro-organism.

Cause undesirable side effects. May not be used in some patients. Eliminate the normal micro-organism in patients’ guts.