immune system. functions of immune system protect against infection by microbes. isolate or remove...
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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.