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Humoral Immune Response

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Wh at Is Humoral Immune

Response

This is immune response t hat is med iated byant ibod ies secreted by t he B lymp hocytes

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Bas ic Structure o f an A nt ibody

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M ec han ism o f Humoral Immun ity

* A nt ibod ies induce res istance t h roug h:

1) A nt itox in neutral ize bacter ial tox ins (d iph ther ia, tetanus )

Ant itox in are developed act ively as a result o f:

a- Prev ious inf ect ion

b- A rt ificial immun izat ion

c- Trans f erred pass ively as ant iserum

* Neutral izat ion o f tox in w ith ant itox in prevents a comb inat ion w ith

t issue cells

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M ec han ism o f Humoral immun ity2) A nt ibod ies attac h to t he sur f ace o f bacter ia and :

a- act as opson ins and en hance p hagocytos is

A n opsonin is any molecule t hat acts as a b ind ing en hancer f or t heprocess o f phagocytos is.

b- prevent t he ad herence o f m icroorgan isms to

the ir target cells, e.g. Ig A in t he gut

c- A ct ivate t he complement and lead to bacter ial lys is

d- Clump bacter ia lead ing to p hagocytos is

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RECOGNITION and A CTIVATION

PHA SEThe Humoral response starts w hen a cell o f the immune system engul f s an ant igen.

Ins ide t he cell, t he new ves icle is called aphagosome.

The p hagosome f uses w ith a alysosome w hich conta ins d igest ive en zymes.

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A CTIVATION PHA SE CON T

The en zymes breakdown t he engul f ed part icleinto f ragments, in a p henomenon calledant igen process ing.

Wi thin t he cells t he processed ant igenscomb ine w ith class M HC prote ins.

The complex is d isplayed on t he macrop hage splasma membrane.

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A CTIVATION PHA SE CON T

This d isplay is known as ant igen presentat ion,and macrop hages are cons idered ant igenpresent ing cells ( A PC).A helper T cell part icipates in t he next stageo f the Humoral immune response.

This helper T cell has T cell receptors t hat canb ind to bot h the class II M HC prote in and t hispart icular presented ant igen. T he helper T-Cellis t he Opson in.

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A CTIVATION PHA SE CON T

This b ind ing tr iggers t he macrop hage torelease cytok ine interleuk in-1, w hich act ivatesthe helper T cell.

The act ivated helper T cell now releases itsown cytok ines, w hich st imulate t he helper Tcell to mult iply.

The cell prol if erates to f orm a clone o f helperT cells, all w ith the same T cell receptors.

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A CTIVATION PHA SE CON T

These receptors are spec ific f or t he ant igen icdeterm inant o f the or iginal processed ant igen.

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THE EFFECTOR PHA SE

The e ff ector p hase beg ins w ith a B cell.

The B cell has membrane bound Ig M receptors

that are spec ific f or t he same ant igen asor iginally engul f ed by t he macrop hage.A n IgM receptor b inds to t he ant igen and t hecell engul f s t he complex by receptor-med iatedendocytos is.

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EFFECTOR PHA SE

The internal ized ves icle f uses w ith a lysosome,which conta ins d igest ive en zymes.

The en zymes d igest t he ant igen, process ing itinto f ragments.

The processed ant igen is t hen attac hed toclass II M HC molecules and d isplayed on t hesur f ace o f the B cell.

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EFFECTOR PHA SE CON T

A helper T cell f rom t he clone o f the helper Tcells in t he act ivat ion p hase can now b ind tothe ant igen d isplayed by t he B cell.

The helper T cell receptor spec ificallyrecogn izes t he ant igen on t he class II M HCprote in.

Upon b ind ing, t he helper T cell releasescytok ines t hat st imulate t he B cell to d ivideand create a clone o f ident ical cells.

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EFFECTOR PHA SE CON TThe result ing B cells develop into e ither long-lived memory cells or into ant ibody-secret ingplasma cells.

Plasma cells have extens ive endoplasm icret iculum and numerous r ibosomes.

Plasma cells are essent ially ant ibody f actor ies

They produce and secrete ant ibod ies o f thespec ificity ident ical to t hat o f the sur f acereceptors on t he parent B cell.

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EFFECTOR PHA SE CON T

Like t he sur f ace Ig M receptors on t he parent Bcell, t he ant ibod ies secreted by t he plasma cellcan b ind to and inact ivate t he or iginal ant igen.

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Stages o f Humoral Immune Response