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APC

Postby nehal » Sun Feb 12, 2006 3:39 am

hello I have FEW questionS
1.A virus normally is inside a cell...how does the antigen PRESENTING CELL recognise it??
according to how much i know,it needs to recognize the MHC class II to trigger signal for the Th cell to release cytokines...which is a very primary need of the immune response....BUT HOW??

2.Also APC cells internalize the antigen(a virus/anythin) either by phagocytosis or endocytosis....what does this mean ...as in does the virus get phagocytosed with the cell it flourishes in...how does it escape the phagolysosomal phase.......and also what exactly is the difference between endocytosis and phagocytosis...
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Postby victor » Sun Feb 12, 2006 12:02 pm

1. Free virus can be arrested by APC but other can be already infiltrated another cells, this condition is taken control by presenting viral antigen by the infected cell (because virus infiltration and replication already changed the cell's surface antigen). The infected cell will also as APC to the specific immune system and the result is: cytotoxicity will occur in that infected cell.

2. Phagocytosis is an endocytosis process done by Phagocytes..:lol:
Some virus have a special ability based on their morphological, physiologycal and biochemistry aspects...so, if they can escape from endolysosomic process, don't be too surprised for that thing..:lol:
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Postby MrMistery » Sun Feb 12, 2006 3:51 pm

Actually there are a lot of differences between phagocytosis and endocytosis. One involves mainly polimerisation of actin molecules outwards while the other involves polimerisation of clatrin molecules inwards... And a lot of other things, which would be useless to post here...

However, to my surprise, Neil Campbell classifies phagocytosis as a type of endocytosis in BIOLOGY 7th edition
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Postby victor » Mon Feb 13, 2006 10:35 am

Ow..:shock: then you should give me that book then..because it contains less detailed informations..:lol:
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Re: APC

Postby Dr.Stein » Mon Feb 13, 2006 11:26 am

nehal wrote:hello I have FEW questionS
1.A virus normally is inside a cell...how does the antigen PRESENTING CELL recognise it??
according to how much i know,it needs to recognize the MHC class II to trigger signal for the Th cell to release cytokines...which is a very primary need of the immune response....BUT HOW??

A virus-infected cell will present modified peptide via MHC-I on its surface. This will attract CTL to kill the cell.

MHC-II is for recognizing external pathogens, MHC-I is for internal pathogens.

nehal wrote:2.Also APC cells internalize the antigen(a virus/anythin) either by phagocytosis or endocytosis....what does this mean ...as in does the virus get phagocytosed with the cell it flourishes in...how does it escape the phagolysosomal phase.......and also what exactly is the difference between endocytosis and phagocytosis...

Antigen is internalized and processed to break up into peptide. Then, the peptide will be externalized to present to T-Cell via MHC-I or MHC-II.
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Postby MrMistery » Mon Feb 13, 2006 6:38 pm

@victor
Poetry is for literature people. We aim to break down and understand, not simplify and memorise(well, Poison's teachers do from what she told us :D ). That's what makes us scientists
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Postby Nite » Sat Feb 18, 2006 3:42 am

how does APC recognise the intracellular viral antigens (peptides or dna/rna)?
before the intracellular viral antigens can bind to MHC class I, some kind of receptors have to bind to the antigens first rite?

Recently, my classmate presented a topic that mention that some APCs expressed TLR3 intracellularly. This TLR3 can then bind to the intracelluar viral dsRNA.. wondering if there are any receptors that can bind to antigen intracellularly?

and also how does the virus break out from the endosome after it has been engulf by the cell??
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Postby victor » Sat Feb 18, 2006 6:22 am

Nite wrote:and also how does the virus break out from the endosome after it has been engulf by the cell??


they fuse their capsids with the endosome and release their genetic materials..
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Postby Dr.Stein » Mon Feb 20, 2006 10:01 am

Nite wrote:how does APC recognise the intracellular viral antigens (peptides or dna/rna)?

For APCs, it is not necessary to recognize whether it is pathogenic or nonpathogenic material. Their job is to process antigens that coming inside our body as much as they can, and present them as peptide with appropriate MHC to T-cell that will recognize and determine whether it is pathogenic or nonpathogenic material. It is T-cell job to take action whether we will generate immun response or immune tolerance.

Nite wrote:before the intracellular viral antigens can bind to MHC class I, some kind of receptors have to bind to the antigens first rite?

We have three professional APCs i.e. dendritic cells (DC), macrophage (MΦ) and B-cell. As you may know, in innate immunity DC and MΦ have a job to engulf nonspecific antigens by pattern recognition, via FcR (Fc reseptor), complement system, etc. Here, to bridge between innate and adaptive immunity, after engulf antigen, they will process and externalize them to be presented with appropriate MHC. B-cell has a BCR (B-cell receptor, similar as Ig but bound on the surface of B-cell) to bind specific antigens and then internalize and externalize with the same mechanism as the former two APC. Virus-infected cell can also act as APC to present viral antigens after with MHC-I (new-made).

Nite wrote:Recently, my classmate presented a topic that mention that some APCs expressed TLR3 intracellularly. This TLR3 can then bind to the intracelluar viral dsRNA.. wondering if there are any receptors that can bind to antigen intracellularly?

Oh a nice topic! Very nice! I never read about this before. If you don't mind, could you please send me the paper please? I'll be more than happy to get it. Thanks in advance :D

However, since this is new to me, I try to digest your question. I am a bit confused to this question. TLR3 is an internal receptor for virus. If this TLR3 is a family of Toll-like receptor, means that it will bind nonspecifically to virus before it comes into nucleus to hijack infected-cell's DNA. In cytoplasm there is a giant protein complex known as proteasome that will cut viral protein into peptides. After some steps of reaction (if you need this in detail, I'll explain it later, this is a bit complicated), eventually the peptide will bind to newly synthesized MHC-I and externalize to be presented to T-cell. So.. that's it. Is this what you want to know or...? :roll: I hope I provide a good explanation :)

Nite wrote:and also how does the virus break out from the endosome after it has been engulf by the cell??

Is virus engulfed and trapped in endosome? I am not sure :? So far I know only its DNA/RNA that come inside the cell. The body of virus is attached aoutside on the surface of the cell membrane. I have no idea about the product (new made virus parts) whether they are packed in endosome or free or bound by some protein or something else. Victor knows about this much better then me ;)

FOR ALL:
I have a nice figure of MHC-I and MHC-II generation. If you think you will understand with this caricature, you can save it; if not then just leave it ;)

MHC class I:
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MHC clas II:
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For myself they are grrreat figures, explain me a lot of things in funny ways :D
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Postby victor » Tue Feb 21, 2006 12:50 pm

Dr.Stein wrote:
Nite wrote:and also how does the virus break out from the endosome after it has been engulf by the cell??

Is virus engulfed and trapped in endosome? I am not sure :? So far I know only its DNA/RNA that come inside the cell. The body of virus is attached aoutside on the surface of the cell membrane. I have no idea about the product (new made virus parts) whether they are packed in endosome or free or bound by some protein or something else. Victor knows about this much better then me ;)


some types of viruses can send their capsides along with their genetic material via endosome..(usually for the lipid enveloped virus). It's due to prevent the Viruses' genetic material from nuclease inactivation in cytoplasm.
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Postby Dr.Stein » Wed Feb 22, 2006 9:27 am

Ah ya, true. By covering their 'body' in lipid envelope, they can diffuse cell membrane easily and slap! they come inside the cell and ready to hijack it. Thanks for reminding me this mechanism, my dear ;)
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Postby victor » Thu Feb 23, 2006 7:38 am

*sigh*....'hijack' word is easy to be written but the truth is...so hard for me to define it...:lol:
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