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EnteryEntery

Viruses enter the "ody in three main #aysViruses enter the "ody in three main #ays

&&

i.i. 'nhalation'nhalation& ia the respiratory tract.& ia the respiratory tract.ii.ii. 'n$estion'n$estion& ia $astrointestinal tract.& ia $astrointestinal tract.

iii.iii. 'noculation'noculation& throu$ht s!in a"rasions,& throu$ht s!in a"rasions,

mucous mem"ranes (e.$. se)ualmucous mem"ranes (e.$. se)ualtransmission* and ia the "ite of antransmission* and ia the "ite of an

arthropod ector.arthropod ector.

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HOST RESPONSE TO V'RS 'N-ET'ONHOST RESPONSE TO V'RS 'N-ET'ON

 The "ody defence mechanisms to irus infection are of The "ody defence mechanisms to irus infection are oft#o types&t#o types&

/./. Non speci0cNon speci0c

1.1. Speci0cSpeci0c

Non2speci0c defence mechanismsNon2speci0c defence mechanisms

 The "ody has defences #hich are not speci0cally The "ody has defences #hich are not speci0callydirected at particular infectious a$ents, "ut #hichdirected at particular infectious a$ents, "ut #hichsere as non2immunolo$ical "arriers to infection.sere as non2immunolo$ical "arriers to infection.

/./. S!inS!in& an e3ectie and impermea"le "arrier unless& an e3ectie and impermea"le "arrier unless"reached "y in4ury, disease, etc."reached "y in4ury, disease, etc.

1.1. Respiratory tractRespiratory tract& up#ard 5o# of mucus "y cilliated& up#ard 5o# of mucus "y cilliatedephithelium remoes irus particles to preentephithelium remoes irus particles to preentinasion of the lo#er respiratory tractinasion of the lo#er respiratory tract

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Non2speci0c defence mechanismsNon2speci0c defence mechanisms continuecontinue

6.6. 7astrointestinal tract7astrointestinal tract& stomach acid& stomach acidinactiates acid2la"ile iruses& "ileinactiates acid2la"ile iruses& "ile

(#hich lyses eneloped iruses*,(#hich lyses eneloped iruses*,

moement of intestinal contents andmoement of intestinal contents andupta!e of irus "y lymphoid tissue allupta!e of irus "y lymphoid tissue all

aid elimination of in$ested iruses.aid elimination of in$ested iruses.

8.8. rinary tractrinary tract& 5o# of urine e)erts a& 5o# of urine e)erts aprotectie 5ushin$ e3ect.protectie 5ushin$ e3ect.

9.9. on4unctiaon4unctia& tears 5ush iruses from& tears 5ush iruses from

the eyethe eye

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Non2speci0c defence mechanismsNon2speci0c defence mechanisms continuecontinue

:.:.

Pha$ocytosisPha$ocytosis

& an important defence mechanisms in "acterial& an important defence mechanisms in "acterial

infection and pro"a"ly in irus infections also inadin$ iruses+infection and pro"a"ly in irus infections also inadin$ iruses+li!e "acteria ; are in$ested "y t#o types of scaen$er cell.li!e "acteria ; are in$ested "y t#o types of scaen$er cell.

i.i. Neutrophil polymorphonuclear leucocytesNeutrophil polymorphonuclear leucocytes

ii.ii. Macropha$es (or mononuclear cells of the reticuloendothelialMacropha$es (or mononuclear cells of the reticuloendothelialsystem*+of t#o types&system*+of t#o types&

a.a. -ree macropha$e in lun$ aleoli, peritonium-ree macropha$e in lun$ aleoli, peritonium

".". -i)ed macropha$es in lymph nodes, spleen, lier (actiated? "y cyto!ines released "y T lymphocytes(a speci0c immune mechanism* hae increased "y pha$ocytic(a speci0c immune mechanism* hae increased "y pha$ocytic

actiity and are attracted "y chemota)is to the site of infectionactiity and are attracted "y chemota)is to the site of infection  

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Speci0c immunolo$ical defenceSpeci0c immunolo$ical defence

mechanismsmechanisms

'mmunolo$ical response are of t#o types &'mmunolo$ical response are of t#o types &

Main e3ect&Main e3ect&

/./. HumoralHumoral & Neutrali=ation of iruses& responsi"le for& Neutrali=ation of iruses& responsi"le forprotectie immunity.protectie immunity.

1.1. ellularellular & @ocali=es lesions% !ills irus ; infected cells& @ocali=es lesions% !ills irus ; infected cells

HMORA@ (ANT'BODC* RESPONSEHMORA@ (ANT'BODC* RESPONSE

@i!e other infectious a$ents, iruses induce production of@i!e other infectious a$ents, iruses induce production ofanti"odies in "lood.anti"odies in "lood. Anti"odies are&Anti"odies are& 

i.i. Immunoglobulins:Immunoglobulins: proteins #hich react speci0cally #ithproteins #hich react speci0cally #ith

anti$ens+#hich are also usually proteins+$enerally on theanti$ens+#hich are also usually proteins+$enerally on thesurface of irus particles.surface of irus particles.

ii.ii. Produced by plasma cells.Produced by plasma cells. -ormed #hen B2lymphocytes are-ormed #hen B2lymphocytes areactiated "y encounter #ith anti$en. B2lymphocytes haeactiated "y encounter #ith anti$en. B2lymphocytes hae

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Speci0c immunolo$ical defence mechanismsSpeci0c immunolo$ical defence mechanisms continuecontinue

immuno$lo"ulin on their surface #hichimmuno$lo"ulin on their surface #hichacts as receptor for irus anti$en. Helperacts as receptor for irus anti$en. Helper

 T cells contri"ute to the di3erentiation of T cells contri"ute to the di3erentiation of

B cells to plasma cells.B cells to plasma cells.iii.iii. Structure :Structure :  C2shaped. The stem is the -c C2shaped. The stem is the -c

fra$ment #hich actiates complementfra$ment #hich actiates complement

and "ind to receptors on infected hostand "ind to receptors on infected host

cells% the t#o arms are the -a"cells% the t#o arms are the -a"fra$ments and contain the anti"ody2fra$ments and contain the anti"ody2

com"inin$ sites.com"inin$ sites.

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Speci0c immunolo$ical defence mechanismsSpeci0c immunolo$ical defence mechanisms continuecontinue

 Three main immuno$lo"ulins Three main immuno$lo"ulins are responsi"le for humoralare responsi"le for humoralimmunity in irus infections&immunity in irus infections&

i.i. '$M'$M% the earliest anti"ody produced% formed a"out a% the earliest anti"ody produced% formed a"out a#ee! after infection, it persists for a"out 82: #ee!s,#ee! after infection, it persists for a"out 82: #ee!s,sometimes lon$er&a pentamer of 0e '$7 molecules.sometimes lon$er&a pentamer of 0e '$7 molecules.

ii.ii. '$7'$7& formed later than '$M "ut persists lon$ term+& formed later than '$M "ut persists lon$ term+often for years. Responsi"le for the immunity tooften for years. Responsi"le for the immunity toreinfection.reinfection.

iii.iii. '$A'$A& a dimeric molecule& found in "ody secretions (as& a dimeric molecule& found in "ody secretions (as#ell as "lood*, i.e. salia, respiratory secretions,#ell as "lood*, i.e. salia, respiratory secretions,tears and intestinal contents% the main anti"odytears and intestinal contents% the main anti"ody

inoled in immunity to respiratory iruses and forinoled in immunity to respiratory iruses and for$ut immunity assosiated #ith enteric irus infection.$ut immunity assosiated #ith enteric irus infection.Secretory '$A acuires a car"ohydrateSecretory '$A acuires a car"ohydrate >transport>transportpiece?piece? in e)tracellular 5uids that is a"sent in serumin e)tracellular 5uids that is a"sent in serum'$A'$A

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E@@@AR RESPONSEE@@@AR RESPONSE

ellular immunityellular immunity is the mechanism for elimination of irus2infectedis the mechanism for elimination of irus2infectedirus cells.irus cells.

't is mediated "y three types of T or thymus2dependent't is mediated "y three types of T or thymus2dependentlymphocytes& helper Tcells, supressor T cells, cytoto)ic T cells.lymphocytes& helper Tcells, supressor T cells, cytoto)ic T cells.

ell2mediated immune response to irus.ell2mediated immune response to irus.

PrincipallyPrincipally

 directed a$ainstdirected a$ainst

irus2infected cells, the response is e)tremely comple) andirus2infected cells, the response is e)tremely comple) andinoles other cells and cyto!ines, in addition to lymphocytes.inoles other cells and cyto!ines, in addition to lymphocytes.

Virus is reco$ni=ed as anti$en "y helper T cells #hen presented "yVirus is reco$ni=ed as anti$en "y helper T cells #hen presented "ymacropha$e or dendritic cell (found in lymph nodes and s!in*macropha$e or dendritic cell (found in lymph nodes and s!in*actin$ as an anti$en2presentin$ cell& reco$nition is dependent onactin$ as an anti$en2presentin$ cell& reco$nition is dependent on

H@A lass '' molecules, i.e. ma4or histocompati"ility (DR*H@A lass '' molecules, i.e. ma4or histocompati"ility (DR*anti$ens, of the macropha$e "ein$ compati"le #ith those on theanti$ens, of the macropha$e "ein$ compati"le #ith those on thehelper T cellshelper T cells

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E@@@AR RESPONSEE@@@AR RESPONSE continuecontinue

Helper T cellsHelper T cells stimulate the cytoto)icstimulate the cytoto)iccellular response and cause actiation ofcellular response and cause actiation ofB cells (the anti"ody2producin$*& theseB cells (the anti"ody2producin$*& thesee3ecfs are produced "y secretion ofe3ecfs are produced "y secretion ofcyto!ines, e.$. interleu!in '@21.cyto!ines, e.$. interleu!in '@21.

Supressor T cellsSupressor T cells control and re$ulate thecontrol and re$ulate thecytoto)ic cellular response "y supressioncytoto)ic cellular response "y supression

of T helper cells.of T helper cells.ytoto)ic T cellsytoto)ic T cells are the main e3ector cellsare the main e3ector cells

#hich !ill irus ;infected tar$et cells.#hich !ill irus ;infected tar$et cells.

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E@@@AR RESPONSE continueE@@@AR RESPONSE continue

@ysis of irus2infected cells is mediated "y seeral@ysis of irus2infected cells is mediated "y seeralmechanisms&mechanisms&

/./. Anti"ody2independent or direct !illin$ "y &Anti"ody2independent or direct !illin$ "y &i.i. ytoto)ic T cellsytoto)ic T cells

ii.ii. Natural !iller (N

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'nterferons'nterferons'nterferons are cyto!ines #hich act to render'nterferons are cyto!ines #hich act to render

cells refractory to irus infectioncells refractory to irus infection

'nterferons hae anti2proliferatie actiity on'nterferons hae anti2proliferatie actiity on

cells and the immune system, as #ell as oncells and the immune system, as #ell as onirus replication.irus replication.

Antiiral chemotherapyAntiiral chemotherapy

interferons #ere lon$ thou$ht to "e potentiallyinterferons #ere lon$ thou$ht to "e potentially

ideal chemotherapeutic a$ents a$ainstideal chemotherapeutic a$ents a$ainst

iruses, "ut this potential has not "eeniruses, "ut this potential has not "een

reali=ed in practice.reali=ed in practice.

E@@@AR RESPONSE continueE@@@AR RESPONSE continue