Blood Lec 19 by Dr Sadia

7/30/2019 Blood Lec 19 by Dr Sadia

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There are two types of MHC

proteins:

(1)MHC I proteins, which present

antigens to cytotoxic T cells,

(2) MHC II proteins, which presentantigensto T helper cells.


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e ant gens on t e sur ace o ant gen-presenting

cells bind with receptor moleculeson the

surfaces ofTcells in the same way thatthey bind with plasma protein antibodies.These receptor molecules are composed of a

variable unit similar to the variable portionof the humoral antibody, but its stemsection is firmly bound to the cell membrane

of the T lymphocyte. There are as many as 100,000 receptorsites on a single T Lymphocyte.


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Different Types of T Cells and TheirDifferent Functions

(1)helper T cells, (2) cytotoxic T cells,

(3) suppressorT cells.

Helper T CellsTheir Role in Overall Regulationof Immunity

Helper T cells are most numerous of the T cells,usually constituting more than three quarters ofall of them.


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Helper T Cells

Serve as the major regulator of all immunefunctions by forming a series of proteinmediators called lymphokines,.


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Among the impt lymphokines secreted by the helperT cells are:

Interleukin-2

Interleukin-3 Interleukin-4 Interleukin-5 Interleukin-6

Granulocyte-monocyte colony-stimulating factor Interferon-gamma


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Specific Regulatory Functions ofthe Lymphokines.

Absence of the lymphokines from the helper Tcells, remainder of the immune system is almostparalyzed.

Helper T cells are inactivated or destroyed by the(AIDS) virus, leaves the body unprotected

against infectious disease,


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Specific regulatory

functions of Helper T cells

Stimulation of Growth and Proliferation ofCytotoxic Cells and Suppressor T Cells. interleukin-2.

Stimulation of B-Cell Growth and Differentiation toForm Plasma Cells and Antibodiesinterleukins 4,

5, and 6 also known as B-cell stimulating factors.


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Activation of the Macrophage System

Slow or stop the migration of themacrophages great accumulation ofmacrophages in inflamed area.

Activate the macrophages to cause farmore efficient phagocytosis.


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Feedback Stimulatory Effect on theHelper Cells Themselves.

Interleukin-2, have a direct +ve

feedback effect in stimulatingactivation of the helper T cellsthemselves.


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Cytotoxic T Cells

Cytotoxic T cells or killer cell are Tlymphocytesdirectly attack & kill othercells.

They are particularly responsive to

Cells of transplanted tissues & organs, Cancer cells Host cells that are infected with viruses,


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Cytotoxic cell recognizes a complex ofantigen and MHC-I protein on a diseasedor foreign cell or antigen presenting cell.

Receptor proteins on thesurfaces of thecytotoxic cells bind tightly to thoseorganisms or cells that contain theappropriate binding-specific antigen.


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After binding, the cytotoxic T cell secretes:

(1) hole forming protien calledperforins

punchround holes in the memb of theattacked cell.

Fluid flows rapidly into the cell from the

interstitial space

attacked cell becomesgreatly swollen, dissolves.

Cytotoxic T cell releases cytotoxicsubstances directly into the attacked cell.


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(2) Lymphotoxin, destroys the

target cells DNA (3) Tumor necrosis factor (TNF)

kills cancer cells & stimulatesfever,leukopoiesis,& eosinophil

activity. (4) interferon, inhibits the

replication of viruses,

(5) interleukins

regulatemacrophage activity, .


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1. Antigen

recognition

2. Costimulation

3. Clonal selection

4. Lethal hitMHC-I

protein

MTC TH

Costimulation

protein

MHC protein

Antigen

APC

TC or TH

TC

TH

APC


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Suppressor T Cells

Suppressor T cells suppressing the functions ofboth cytotoxic & helper Tcells.

Suppressor T cell preventing the cytotoxic Tcells from causing excessive immune reactionsthat might be damaging to the bodys own tissues

. Suppressor cells & helper T cells, are regulatory

T cells.

Suppressor T-cellsyst plays an impt role inlimiting the ability of the immune system toattack a persons own body tissues, called immunetolerance.


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Tolerance of the Acquired Immunity System to OwnTissues

Immune mechanism normally recognizes apersons own tissues being distinctive frombacteria or viruses, and forms few antibodies oractivated T cells against his or her own antigens.

Most tolerance develops during preprocessing ofT lymphocytes in the thymus & B lymphocytes inthe bone marrow.


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During the preprocessing oflymphocytes all or most of those

clones of lymphocytes that arespecific to damage the bodys owntissues are self-destroyed.


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Failure of the Tolerance MechanismCauses Autoimmune Diseases.

Sometimes people lose their immunetolerance of their own tissues.

It occurs after destruction of some of thebodys own tissuesreleases self-antigens circulate in the body cause

acquired immunity


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Several specific diseases thatresult from autoimmunity

(1) Rheumatic fever

(2)Glomerulonephritis

(3) Myasthenia gravis (4)Lupus erythematosus,


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Immunization by Injection ofAntigens

1.By njecting dead organisms not capable ofcausing disease but have chemical antigens.

It is used against typhoid fever, whooping cough,diphtheria,& other bacterial diseases.

2.Immunity can be achieved against toxins thattreated with chemicals. It is used in immunizationagainst tetanus & botulism.


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Person can be immunized by beinginfected with live organisms that havebeen attenuated.

This is used to protect againstpoliomyelitis, yellow fever, measles,smallpox, and many other viral diseases.


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Passive Immunity

Done by infusing antibodies, activated T cells, or boththat has been actively immunized against the antigen.

Antibodies last in the body of the recipient for 2-3weeks, & during that time, the person is protectedagainst the invading disease.

Activated T cells last for a few weeks if transfusedfrom another person & only for a few hrs to a few daysif transfused from an animal.

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Blood Lec 19 by Dr Sadia