Organs and cells

8/7/2019 Organs and cells

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Cells and Organs of the immunesystem


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T he tissues of the immune systemfall into two groups based upon

their role in host defense:P rimaryS econdary


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P rimary (or central) create andeducate them during theirdifferentiation into mature cells: bonemarrow and thymus gland.

S econdary (peripheral) immuneorgans look after mature cells thatare an active part of defense: thespleen, the lymphatic system, lymphnodes.


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LYMPHOID TISSUES

Thymus(T-cell maturation)

Bone marrow Lymph nodes Spleen

Primary Secondary(Responsible for maturation of Ag-reactive) (Sites for Ag contact and response)

cells)


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T he circulatory system transportsthe components of the immunesystem, serve as a highway for thetransport of immune cells.


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T he major cell types found in blood arered blood cells, whose role is to transportoxygen and carbon dioxide into and out of

the body respectively. Blood contains manytypes of white blood cells, which are madeup of mainly neutrophils, but alsomonocytes, T- lymphocytes and B -lymphocytes.


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Serumand

Plasma


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Components of blood


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Bone marrow is the origin of all immune cells.

- Stems cells in the bone marrow are theprogenitors (forefathers) of all immune cells.

-S tems cells constantly divide and differentiateinto various types of immune cells under theinfluence of cytokines ( Cytokines are smallsignaling proteins that help to regulate thebehavior of the cells of the body).

LYMPHOID TISSUES

Primary:Bone marrow


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C ells made in bone marrow:

1- Red blood cells2-White blood cells ( cells of the immunesystm)3- Platelets

T he major cell type made by the bone marrow isred blood cells. Platelets also form in the bonemarrow and assist in formation of blood clotsfollowing any kind of injury. Neither of these celltypes plays a role in the immune response,


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LYMPHOID TISSUESPrimary: Bone marrow


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T ypes of immune cells and their progenitors

S tem cells in the bone marrow, under the influence ofdifferent cytokines, differentiate into different types ofimmune cells.

Naturalkiller cell


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lymphocytes:

a.Lymphocytes mediate the adaptiveimmune responses.

b. Only a small proportion of the body'slymphocytes are found in the blood. Themajority are found in lymphoid tissue . Infact the collective mass of all thelymphocytes in the human body is aboutthe same as the mass of the brain!


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c. Lymphocytes circulate back andforth between the blood and thelymphoid system of the body.

d. T hey have a life span of days to

years.

lymphocytes:


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Lymphocytes:

T here are 3 major populations oflymphocytes:

A: B cells (bone marrow)B: T Cells (maturation:thymus)

C: Natural killer (NK)cells


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LymphocytesA: B Lymphocytes

M ediate humoral immunity : the production ofantibody molecules against a specific antigen.

have B-cell receptors (BCR) for antigenrecognition.

Once activated, mostB- lymphocytesdifferentiate intoantibody - secreting

plasma cells .


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Some markers expressed on B cellAg recognition(BCR: B cell receptor)

Ag presentationMHC


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B. T-lymphocytes (T-cells):

- C ell-mediated immunity , the production ofcytotoxic T-lymphocytes ( C TLs), which

can kill the infected cell.-T wo subtypes:

T4 :surface marker: CD 4T8 : S urface marker: CD 8

Lymphocytes


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Some markers expressed on T cell

Antigenrecognotion)


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C. Natural killer (NK) cellsare large granular lymphocytes: lack B-

cell receptors and T-cell receptors

detect and killsome infected host cells,

including tumor cells,virus, or intracellularbacteria - infected cells.

Lymphocytes


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MHCII

T Cell

Lymphocytes


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T ypes of immune cells and their progenitors

S tem cells in the bone marrow, under the influence ofdifferent cytokines, differentiate into different types ofimmune cells.

Naturalkiller cell


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F unction:

take up large particulate antigens, pieces oftissue, old cells, bacteria by phagocytosis .

they can act as antigen processingpresenting cells ( APC ) for T cells.

P roduction of important immune proteins andpeptides. S uch as transferrin (an iron -binding protein), complement proteins andvarious cytokines necessary for immune

function.


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When they migrate to tissue arecalled M acrophage :F

or example macrophages in the liver,called Kupffer cells, phagocytize olderythrocytes from the blood and removethem.


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M acrophages in various

tissuesName of macrophageAlveolar macrophage

H istiocyteKupffer cellM icroglial cellOsteoclast

T issueLungConnective tissuLiverNeural tissueBone


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3) GRANULOCYT ES

T here are three types ofgranulocyte:

a.Neutrophils

b.EosinophilsC. Basophils

Cells of the immune system


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3) GRANULOCYT E S

a.Neutrophils are the most commontype of polymorphonuclear cells,making up 90% of granulocytes in theblood.F unction: phagocytsis

Neutrophil(Segmented


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b. Eosinophils make up 2- 5% ofgranulocytes in the blood, but thisnumber can rise considerably inpeople with parasitic diseases as wellas asthma, eczema or other diseasesassociated with allergies.

3) GRANULOCYT E S


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Eosinophils primarily found in the blood,but also near epithelia that have highbacterial populations (e.g., intestines,vagina, nasal passages). Eosinophil granulescontain a number ofdifferent enzymesincluding,

acid phosphatase,glucuronidase andperoxidase.


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Eosinophils combat antigenic challenges toobig to be attacked by phagocytes. S uch asparasitic worms or helminths. In battling

these infections, the body will first coverthe worm with antibody. T his then activateseosinophils, which bind to the parasite andrelease the contents of their granules, thuscausing external digestion of the worm.


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C. Basophils normally make up0-1% of thWBCs , Basophils release histamine , and

prostaglandins , chemicals that promotesinflammation by causing vasodilation,increasing capillary permeability,

3) GRANULOCYT E S


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Mast cellsT hey are found throughout the body inlymph nodes, spleen, bone marrow, aroundblood vessels, nerves, glands and in theskin. M ast cells have granules that, likebasophils, contain histamine. they

participate in immuneresponses to gram - negative

bacteria and allergic reaction.

Cells of the immune system


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LYMPHOID TISSUES

Thymus(T-cell maturation) Bone marrow

Lymph nodes Spleen

Primary Secondary

(Responsible for maturation of Ag-reactive) (Sites for Ag contact and response)

cells)


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Other specialized structures of thelymphoid system are the lymphaticvessels , which connect most tissues inthe body with lymph nodes and eventuallywith the blood stream. It is a branching

system whose vessels get ever smaller asit penetrates tissue.

lymphatic system


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Unlike the blood system, the lymphaticsystem is not circular, but ends in blindcapillaries. T he system focuses its

attention on areas of the body that aremost likely to be entry points forpathogens: skin dermis, respiratory tract,gastrointestinal tract and genitourinarytract mundane


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Cells and fluids are exchanged between blood andlymphatic vessels, enabling the lymphatic system tomonitor the body for invading microbes. T he lymphaticvessels carry lymph, a clear fluid that bathes thebodys tissues.


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T he thoractic(largets lymphaticvessle) duct collects liquid from the

lymph system and returns it to thecirculatory system( see next figure).


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Ly mphatic

system

via

thoracic ductand

right l ymphatic duct


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Secondary organs1. Lymph nodes

2. Spleen3. MALT

Here, lymphocytes encounter Ag andundergo antigen-dependentdifferentiation

LYMPHOID TISSUES


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1.Lymph nodes J unctional filters in the lymphaticsystem

F unctions:1. S upport the proliferation and

differentiation of lymphocytes2. Acts as a junction between the

lymphatic system and the

circulatory system


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Small, bean-shaped lymph nodes are lacedalong the lymphatic vessels. Each lymphnode contains specialized compartmentswhere immune cells assemble, and wherethe can encounter anti ens.

Ag &Ab

encounterPlasmacells(Absecerting)


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2.Spleen- Largest lymphatic organ:-T wo areas:

Red pulp : F ilters old and damaged RBCWhite :pulp F ilters antigen from the blood

Lymphocytes traffic through the spleencompletely by blood circulation


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Spleen


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3. MALT (M ucosa- Associated Lymphoid T issue)

Distributed throughout of GI,

respiratory and GU tractrespiratory adenoid, tonsil,digestive Peyers patches,

appendix

Large amount of IgA is secreted

Collection of lymphoid cells: M alt

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Major Tissues

Primary Lymphtissues Cells originate

or mature

SecondaryLymph Tissues

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Organs and cells