defence mechanism of body

8/6/2019 Defence Mechanism of Body

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Defense Mechanism of the Body

Tika Ram Gurung

Coordinator

Oasis Medical College



�Defense mechanism literally or etymologically it

means:

� Defense: Protection against attack

� Mechanism: the system or the way in which somethingworks

� Body: the physical form of person or animal

�Hence, defense mechanism of body is also termed

immunity, may be defined as, the system or theway in which the body protects itself against the

attack of microorganism.



�Human body continuously encounters with

potentially pathogenic microorganisms.

� Infections and diseases are usually prevented or

minimized because a healthy body has a range of

defense mechanisms to protect them, called

Immunity. The study of defense mechanisms of

body is called Immunology.



� External defense mechanism (1st line of

defense)

� Internal defense mechanism

Non specific defense mechanism (2nd line of defense)

Specific defense mechanism (3rd line of defense)



� It comprises following:

� Skin

� Mucous membrane

� Chemical factors

� Skin: Skin is hostile to microorganism because it

consists of tissues, which are keratinized and water

proof.

� It has number of sebaceous gland that consists of

sebum, which is antimicrobial.



� Normal flora present on the skin produces unsaturated

fatty acid, which prevent the entry of other foreign

organism.

� Mucus Membrane: the mucus membrane contain

mucous gland which secret mucus. In addition, this

mucous contains lysozyme, which is anti-microbial.

�Chemi cal f actor : pH of the gastro-intestinal tract,

i.e., stomach is almost 1 to 2 pH, which is acidic and is

unfavorable for micro-organism which are pathogenic.



� Internal defense mechanism refers to phagocytic

cells, interferon, natural killer ( NK) cells, humoral

immunity (bone marrow derived lymphocytes; B-

cells) cellular immunity (thymus derivedlymphocytes; T-cells) or combination of these

(both B and T cells).

� It can be further classified in two categories,� Non specific defense mechanism &

� Specific defense mechanism



Non specific defense mechanism &� There are different mechanisms involved in non-

specific defense mechanism.

�

They include;� Phagocytic cell,

� Interferon and,

� Natural killer cells

� P hagocyt i c cell : Phagocytic cells are a group of WBCi.e., neutrophill and monocyte.

� They can engulf foreign particles or mocro-organism,and also called eat cells.



� I nter f eron: Interferon are the defensive protein

synthesized by the host cell.

� They are non-specific to bacteria but plays important rolein case of viruses or viral infections.

� They do not attack bacteria but attack different types of

viruses.



� N atural ki ller cells: Nk cells are large granular cells,

morphologically quite similar to lymphocytes.

� They are thought to be important in resistance to virusinfections and probably also in malignancy.

� They are actually lymphocyte and are very important

cells to provide immunity.

� It can destroy virally infected cells and tumors cells.



� It is also called 3rd line defense, which acts against

of specific group of micro-organism when foreign

body enters into the host cell.

�Active immunity Humoral immunity

Cellular immunity

Combination of the above� Passive immunity

Immunoglobulin



� It is the immunity which an individual develops as aresult of infection or by specific immunization and isusually associated with presence of antibodies or cellshaving a specific action on the microorganismconcerned with a particular infectious disease or on itstoxin.

� In the other words, active immunity depends upon thehumoral and cellular responses to the host.

� The immunity produced is specific for particular disease, i.e., the individual in most cases is immune tofurther disease with the same organism or or antigenically related organism for varying periodsdepending upon the particular disease.



� Active immunity may be acquired in 3 ways:

� Following clinical infection, e.g., chickenpox, rubella andmeasles.

� Following subclinical or inapparent infection, e.g., polio anddiphtheria

� Following immunization with an antigen which any be akilled vaccination, a live attenuated vaccine or toxoid.

� Expanded program of immunization is good examplefor active immunization, which includes vaccinesagainst TB, Polio, Diphtheria, Pertusis, Hepatitis- B,Tetanus and Measles. (JE in endemic area)



�Humoral immunity comes from the B-cells (bone-

marrow derived lymphocytes) which proliferate

and manufacture specific antibodies after antigen

presentation by macrophages.

�The antibodies are specific, i.e., they react with the

same antigen which provoked their production, or

a closely related one.



�Although antibodies are quite effective in

combating most infectious diseases, humoral

immunity does not cover all the situation that one

finds in infectious diseases.

� For example, some pathogens e.g., M. Leprae, M.

tuberculosis, and many viruses escape the

bactericidal action of leukocyte.



�They can even multiply in the mononuclear

leukocyte. However, these macrophages can be

stimulated by specific stimulated by substances

secreted by specific stimulated T-lymphocytes.

�The activated macrophages perform a much more

efficient phagocytic function than non-activated

macrophages.



� In addition to the B and T lymphoid cells which

are responsible for recognizing self and non-self,

very often, they co-operate with one another and

with certain accessory cells such as macrophagesand human K (K iller ) cells, and their joint

functions constitute the complex events of

immunity.



� When antibodies produced in one body are transferredto another to induce protection against disease, it isknown as passive immunity.

� In other words, the body does not produce its ownantibodies but depends upon ready-made antibodies.Passive immunity may be induced:

� By administration of an antibody-containing preparation(immunoglobulin or antiserum)

� By transfer of maternal antibodies across the placenta.Human milk also contains protective antibodies, (IgA)

� By transfer of lymphocytes, to induce passive cellular immunity- this procedure is still experimental.



� Immunoglobulin are synthesized by plasma cells

and also by lymphocytes.

� It makes 20-25% of total serum protein.

� Immunoglobulin are of 5 types based on their size,

carbohydrate content and amino acid analysis.

�These are IgG, Ig-A, Ig-M, Ig-D, and Ig-E.



� I gG : is the major serum immunoglobulin in

antibacterial immunity.

� In healthy adults it accounts for more than 70% of

the immunoglobulin.

� In man, IgG is only a immunoglobulin that is

transported across the placenta to reach the fetus

and provide the newborn baby with passivelyacquired antibody during its early life.



� I gA: consists 10% of total serum globulin, which

is found in body concentrations i.e., blood stream,

saliva, genital secretion, colostrums, tears,

respiratory, intestinal etc. Its prime function is to promote phagocytosis process.

� I gM : Often called macroglobulin, predominantly

found intravascular and consist of 5-10% of serumimmunoglobulin. It plays an important role in

providing antibacterial activity. Its deficiency is

associated with septicemia.



� I gD: It consisted 0.003 to 0.004 g/litter. IgD is

mostly exclusively found on the surface of

immature lymphocytes and may be involved in

their maturation and regulation.

� I gE : It is very low about of 17-450 ng/ml. It binds

firmly to mast cells and basophiles.

� I gE : antibodies are necessary for immediate

hypersensitivity reaction.



� Herd immunity is as the level of resistance of a

community or a group of people for a particular

disease.

� Herd immunity is a type of immunity that occurs when

the vaccination of the portion of the population

provides protection to un-vaccinated individuals.

� Maximum percentage (>80%) of the community is

immunized the rest of the community people will enjoy

protection for the disease as long as the herd structure

is unaltered.



70 ± 80%

immunized

No disease /

Elimination

Transmission

Block

Primary case-

Zero secondary

case

Primary case-

Less secondary

cases

Decrease

Susceptible



VV

SC

V

U

V

PC

U

V

U

V

U

V

V

V

V

V

V

V

V

V

V

SCSC

SC

defence mechanism of body

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