Blood Lec 17 by Dr Sadia

7/30/2019 Blood Lec 17 by Dr Sadia

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Immunity

Human body has the ability to resist almost alltypes of organisms or toxins that tend to damagethe tissues and organs.

This capability is called immunity.


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Innate immunity

results from generalprocesses

Acquired immunity develops after the body is first attacked by a bacterium, virus, or toxin,

often requiring weeks or months to develop the

immunity.


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Innate immunity

1. Phagocytosis of bacteria and other invaders byWBC and cells of the tissue macrophage system.

2. Destruction of swallowed organisms by the acidsecretions of the stomach and the digestiveenzymes.


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3. Resistance of the skin to invasion byorganisms.

4. Presence in the blood of certain

chemical compounds that attach to foreignorganisms or toxins and destroy them.


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Some of these compounds are:

(1) lysozyme, a mucolytic polysaccharide

attacks bacteriacauses them todissolute;

(2) basic polypeptides, react with &inactivate certain types of gram +vebacteria;


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(3) Complement complexa syst of about20proteins activated in various waysto destroy bacteria

(4) natural killer lymphocytesrecognize & destroy foreign cells,

tumor cells, and infected cells.


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This innate immunity makes the human

body resistant to such diseases as paralytic viral infections of animals,

hog cholera,

cattle plague,

distempera viral disease that kills alarge% of dogs.


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Acquired (Adaptive) Immunity

Ability of the human body to develop extremelypowerful specific immunity against individualinvading agents lethal bacteria, viruses, toxins,and even foreign tissues from other animals.

Called acquired or adaptive immunity.

Acquired immunity iscaused by a special immunesyst antibodies and/or activated lymphocytes

attack and destroy the specific invadingorganism or toxin.


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Basic Types of Acquired Immunity

Two basic types of acquired immunity are:

Humoral immunity or B-cell immunity Body develops circulating antibodies, which are

globulinmolecules in the blood plasma

capable ofattacking the invading agent.

Cell-mediated immunity or T-cell immunity

Formation of large numbers of activated Tlymphocytesin the lymph nodes to destroy theforeign agent.


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Antigen

Both Types of Acquired Immunity are

initiated by Antigens.

Each toxin or organism always contains one or

more specific chemical compounds in its makeupthat are difft from all other compounds.

These are proteins or large polysaccharides

initiate the acquired immunity.

These substances are called antigens.


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Substance to be antigenic,must have a high mol wt,8000 or greater.

Process of antigenicity depends on regularlyrecurring molecular groups, called epitopes, onthesurface of molecule.

Proteins and large polysaccharides are alwaysantigenic, b/c both of these have this

characteristic.


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Lymphocytes Are Responsible forAcquired Immunity

Acquired immunity is the product of the bodyslymphocytes.

People who have a genetic lack of lymphocytes orwhose lymphocytes have been destroyed by radiationor chemicals, no acquired immunity can develop.

Lymphocytes are located in the lymph nodes &lymphoidtissues such as the spleen, submucosal areasof the GIT, thymus, and bone marrow.


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Lymphoid tissue is distributed in the body tointercept invading organisms or toxins before

they can spread too widely.

Invading agent first enters the tissue fluidscarried by way of lymph vessels to the lymph nodeor other lymphoid tissue.

Lymphoid tissue of the GIT is exposed immediatelyto antigens invading from the gut.


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Lymphoid tissue of the throat and pharynxintercept antigens that enter from upper

respiratory tract. Lymphoid tissue in the lymph nodes is exposed to

antigens that invade the peripheral tissues of thebody.

Lymphoid tissue of the spleen, thymus, & bonemarrow plays the specific role of interceptingantigenic agents in circulating blood.


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Two Types of Lymphocytes PromoteCell-Mediated or Humoral Immunity

T lymphocytes, is responsible for cell-mediatedimmunity,

B lymphocytes, is responsible forhumoralimmunity.

Both types of lymphocytes are derived frompluripotent hematopoietic stem cellsthat formlymphocytes.


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All the lymphocytes are preprocessed in the

following ways.

Lymphocytes that form activated T lymphocytesfirst migrate & preprocessed in the thymus gland,

->called T lymphocytes to designate the role ofthe thymus.

B lymphocytes that are destined to formantibodiesare preprocessed in the liver duringmid fetal life and in the bone marrow in late fetallife & after birth.


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This populations of cells was first

discovered in birds, which have a specialpreprocessing organ called the bursa ofFabricius.

These lymphocytes are calledBlymphocytes to designate the role ofthe bursa.


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P f h & B


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Preprocessing of the T& BLymphocytes

All lymphocytes in the body originate fromlymphocyte-committed stem cellsof the embryo,are incapable of forming directly either activatedT lymphocytes or antibodies.

They must be further differentiated in appropriateprocessing areas.


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Thymus Gland Preprocesses theT Lymphocytes

T lymphocytes, after origination in the bonemarrow migrate to the thymus gland dividerapidly develop extreme diversity for reactingagainst difft specific antigens.

One thymic lymphocyte develops specificreactivity against one antigen.


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Next lymphocyte develops specificityagainst another antigen.

This continues thousands of diff typesof thymic lymphocytes with specificreactivities against many thousands ofdifft antigens.


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Difft types of preprocessed T lymphocytes

leave the thymus

spread by way of the bloodthroughout the body lodge in lymphoid tissueeverywhere.

Any T lymphocytes leaving the thymus will notreact against proteins or other antigens that arepresent in the bodys own tissues.


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Thymus selects which T lymphocytes will bereleased by first mixing them with virtuallyall the specific self-antigens from thebodys own tissues

If a T lymphocyte reacts, it is destroyed &

phagocytized instead of being released.


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Cells that are finally released arenonreactive against the bodys ownantigensthey react only againstantigens from an outside source

such as a bacterium, a toxin, or even

transplanted tissue from anotherperson.


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Preprocessing of T lymphocytes in the thymus

occurs shortly before birth of a baby & for

few months after birth.

Beyond this period, removal of the thymusgland diminishes the T-lymphocytic immunesystem.

Removal of the thymus several months beforebirth can prevent development of all cell-mediated immunity.


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Liver and Bone MarrowPreprocess the B Lymphocytes

B lymphocytes are preprocessed in the liverduring midfetal life and in the bone marrowduring late fetal life and after birth.

B lymphocytes are different from Tlymphocytes in two ways:

First, B lymphocytes actively secrete

antibodiesthat are the reactive agents. These are large protein molecules capableof combining with & destroying the antigenicsubstance,.


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Second,

B lymphocytes have even greater diversitythan the T lymphocytes, thus formingmany millions of types of B-lymphocyteantibodies with diff specific reactivities.

After preprocessing, the B lymphocytes,migrate to lymphoid tissue throughout thebody, where they lodge.


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T Lymphocytes and B-LymphocyteAntibodies React Highly

SpecificallyAgainst Specific Antigens


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Specific antigen comes in contact withT& Blymphocytes in the lymphoid tissue,Tlymphocytes activated to form activated Tcells, & B lymphocytes activated to formantibodies.

Activated T cells & antibodies react highlyspecifically against the particular types ofantigens that initiated their development.


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Clone of lymphocytes

All the difft lymphocytes that are capableof forming one specificity of antibody or Tcell are called a cloneof lymphocytes.

Lymphocytes ineach clone are alike & arederived originally from one or a few early

lymphocytes of its specific type


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The Thymus. (a) The thymu s is extremely large in a newbo rn infant.

(b) The adult thym us is atrophied and o ften barely no t iceable


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Blood Lec 17 by Dr Sadia

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