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Account for 0.5% of WB Cs an d: Have U- or S-sha ped nuclei with tw o or three

cons picuous c onstricti ons Are f uncti onally si milar t o mast cells Have large, pur plish-black (bas ophilic)

granules that c ontain hista mineHistamine in f lamm atory che mical that acts as avas odilator an d attracts other WB Cs (antihista minescounter this e ff ect)

Bas ophils

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Agranulocytes ly mphocytes an d monocytes: L ack visible cyt op lasmic granules Are si milar structurally, but are f uncti onally

distinct an d unrelate d cell ty pes

Have s pherical (ly mp hocytes) or kidney-sha ped (mo nocytes) nuclei

Agranul ocytes

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Account for 25% or mo re of WB Cs an d: Have large, dark- pur ple, circular nuclei with a

thin ri m of blue cyt op lasm Are found mo stly en meshe d in ly mphoid tissue

(some circulate in the bl ood )There are tw o ty pes of lymphocytes: T cellsand B cells T cells f uncti on in the i mm une res ponse B cells give rise t o plasma cells, which pr oduce

antib od ies

L ymphocytes

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Monocytes acc ount for 48% of leuk ocytes They are the largest leuk ocytes They have abun dant pale-blue cyt op lasms They have pur ple-staining, U- or kidney-sha ped

nuclei

They leave the circulati on, enter tissue, an d diff erentiate int o macr ophages

Monocytes

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Macr ophages: Are highly mo bile an d actively phag ocytic Activate ly mp hocytes t o mo unt an i mm une

res ponse

Monocytes

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Summ ary of For med Ele ments

Table 17.2

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Summ ary of For med Ele ments

Table 17.2

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L euk opo iesis is h or monally sti mulate d bytwo f amilies of cytokines (he matopo ieticf actors) interleukins an d colony-stimulating f actors ( CSFs) Interleukins are nu m bere d (e.g., I L -1, I L -2),

whereas CSFs are na med for the WB Cs theystimulate (e.g., granul ocyte- CSF sti mulatesgranul ocytes)

Macr ophages an d T cells are the mostimpo rtant s ources of cytokinesMan hemato oietic h or mones are use d

Pr oducti on of L euk ocytes

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For mation of L

euk ocytes

Figure 17.11

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The Immune SystemDefends body against pathogens

Can distinguish between self and non-self

General Defence System (innate)Non-specific = acts against all pathogensRapid

1. First line of general defenceSkin = barrier. Sweat (acidic pH)Clotting = also helps protect skinLysozyme = enzyme in saliva, sweat, tears. Attacks bacterial cell walls

Mucous (respiratory, digestive, urinary & reproductive tracts) = traps pathogensCilia= little hairs that help clear mucous (and pathogens) from respiratory tractAlimentary canal = lysozyme in saliva, stomach HCl kills many pathogens, specialisedimmune areas in the GI tract, very high turnover of epithelial cells, antibodies

Specific Defence System (adaptive)

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2 . Second line of general defencePhagocytic white blood cells (leukocytes) = destroy pathogens that enterComplementInflammation

Phagocytes ( Phago= eat; cyte=cell)attracted to a site of infection ( chemotaxis ) by chemicals released by injured cellsThree types neutrophils (short lived),

monocytes (short-lived..in blood) and macrophages (long-lived..in tissue)

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Macrophages very large white cells that can move

around body, or remain in certain tissues. Long lived,act as scavengers

Immune organs

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Complementset of 30 proteins found in plasma that are activated by

infectioncomplicated chain reaction that leads to the bursting ofviruses and bacteria

made in the liver

Interferonsset of proteins produced by virally infected cells cells to limit the spread of viral

infections, by inducing a state of resistance in healthy cells.induced by viruses, bacteria and other signals from the immune system

Inflammationinfected cells ( mast cells ) release histamine , which is a vasodilator . This causeslocalised swelling, redness, heat, pain. Can also cause high temperature.

brings white cells to the area of infectionAnti-histamines

2 . Second line of general defence cont.

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Comp lement Pathways

Figure 21.5

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Inter f er on (IFN)

Figure 21.4

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N eutrophilsenter blood

from bonemarrow

1

2

3

4

Margination

Diapedesis

Positive

chemotaxis

Capillary wallEndotheliumBasal lamina

Inflammatorychemicalsdiffusing fromthe inflamedsite act aschemotacticagents

n amm a ory es ponse: ag ocy cMo bilizati on

Figure 21.3

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Red bone marrow

1

2

3

Immunocompetent,but still naive,lymphocytemigrates via blood

Mature (antigen-activated)immunocompetent lymphocytescirculate continuously in thebloodstream and lymph andthroughout the lymphoid organs of the body.

Key: = Site of lymphocyte origin

= Site of development of immunocompetence

as B or T cells; primary lymphoid organs= Site of antigen challenge and final

differentiation to activated B and T cellsImmaturelymphocytesCirculation in

blood 11 Lymphocytes destined to become T

cells migrate to the thymus and developimmunocompetence there. B cellsdevelop immunocompetence in redbone marrow.

ThymusBone

marrow

Lymph nodes,spleen, and other lymphoid tissues

2 2 After leaving the thymus or bonemarrow as naive immunocompetentcells, lymphocytes seed the lymphnodes, spleen, and other lymphoidtissues where the antigen challengeoccurs.

3 3

ActivatedimmunocompetentB and T cellsrecirculate in bloodand lymph

Imm unocomp etent B or T cells

Figure 21.8

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Major r olls in i mmunity are: To engul f foreign particles

To present f rag ments of antigens on their ownsur f aces, t o be rec ognize d by T cells

Major AP Cs are dendritic cells (D Cs),macr ophages, an d activate d B cellsThe major initiat ors of ada ptive i mm unityare D Cs, which actively migrate t o thelymph nodes an d secondary ly mphoid

organs an d present antigens t o T an d B cells

Antigen-Presenting Cells (AP Cs)

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Secrete soluble pr oteins that activate T cellsActivated T cells in turn release che micalsthat: Rev u p the maturati on an d mo bilizati on of DCs Pr od macr ophages t o bec om e activate d

macr ophages, which are insatiable phag ocytesthat secrete bacterici dal che micals

Macr ophages an d Den dritic Cells

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Specific Defence System (Adaptive Immune System)

Antigens foreign molecules thatgenerate anti body production

Antibodies (immunoglogulins) proteinsproduced by lymphocytes in responseto antigens

Monocytes develop into macrophages which phagocytose foreign particles ( antigens )Lymphocytes -

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IgD mo nomer attache d to the sur f ace of B cells,impo rtant in B cell activati onIgM penta mer release d by plasma cells duringthe primary i mm une res ponse

IgG

mo nomer that is the mo st abun dant an d diverse antib ody in primary an d sec ondaryres ponse; cr osses the placenta an d conf ers passiveimm unityIgA dimer that hel ps prevent attach ment of

pathogens t o e pithelial cell sur f acesIgE monom er that bin ds to mast cells an d

bas ophils, causing hista mine release whenactivate d

Classes of Antib od ies

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Mechanis ms of Antib ody Acti on

Figure 21.13

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Maj or Ty pes of T Cells

Figure 21.14

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T-lymphocytes

Helper T-CellsRecognise antigens on

surface of leukocytes,especially macrophages

Enlagre and form aclone of T-helper cells

Secrete interferon andcytokines whichstimulate B-cells andstimulate killer -cells

Can be infected by HIV

Killer T-CellsAlso called cytotoxic

Destroy abnormal bodycells, e.g. virus infectedor cancer cells

Stimulated by cytokines(THcells)

Release perforin , whichforms pores in targetcells. This allows waterand ions in = lysis

Suppressor T-CellsControl the

immune systemwhen the antigen/pathogen hasbeen destroyed

Only recentlydiscovered solittle is knownabout them

Memory T-CellsCan survive a long tim

and give lifelongimmunity frominfection

Can stimulate memoryB-cells to produceantibodies

Can trigger productionof killer T cells

Mature in Thymus, which is most active just before and after birth.The thymus starts to shrink during puberty.

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Abnormal cell e.gcancer cell, infected cell

Normal cell

Antigen

Killer T-cellrecognises antigen

Clones of killer T-cellattach to antigen

Helper T-cell stimulatescorrect killer T-cell to

multiply

Killer T-cells releaseperforin pores

Abnormal cell gainswater, swells andbursts

Helper T-cell alsostimulates B-cellsto make antibodies

Memory T-cells stay incirculationSuppressor T-cellsturn off immune

response

X X

X

How T-cells work

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Duration of immunityMemory B-cells circulate for a long time. If the same pathogen infects thebody again, these B-cells can produce large amounts of specific antibodyvery quickly. This is why you usually dont suffer from the same infectiontwice.Memory T-cells survive a long time and trigger an immune response

Tumours in most cases the body recognises tumours as being bad, because theyexpress abnormal molecules on the cell surface. However sometimes the body doesntnotice and cancers can develop

Immune disordersSometimes the body produces antibodies against its own tissues e.g. autoimmunediseases e.g. rhumatoid arthritis, Crohns disease, SCID (bubble boy disease),

asthma

Allergies occur when the body reacts to materials which should notbe antigenic e.g. peanuts

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Induced Immunity

Active immunityProduction of a persons ownantibodies. Long lasting

Passive immunityAn individual is given antibodies by anotherShort-term resistance (weeks- 6months)

Natural ActiveWhen pathogen

enters body in the

normal way, wemake antibodies

Natural PassiveBaby in utero

(placenta)

Breast-fed babies

Artificial PassiveGamma globulin

injection

Extremely fast, butshort lived (e.g. snakevenom)

Edward Jenner

Artificial ActiveVaccination usually

contains a safe antigen

from the pathogen.Person makesantibodies without

becoming ill

yumm y

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Overview of the Immune Response