interferon

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iri_black
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Post by iri_black » Sat Jul 23, 2005 9:36 am

Following phagocytosis of a pathogen, fragments of the pathogen are complexed with MHC proteins and displayed on the surface of the macrophage or dendritic cells of the innate immune system. If the cell encounters a dangerous pathogen, a co-receptor called B7 is produced. This is a crucial step for turning on the adaptive immune response and developing a memory of pathogen threats.

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Post by victor » Sat Jul 23, 2005 11:28 am

IMMSMR, fragments of pathogen that complexed with MHC are called antigens right?? Um, talking about that, I read about super antigen that can't be complexed with either MHC or the variable regio of the T-cell. can someone explain that?? (the book's language is truly difficult to understand.. :( )
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Post by Dr.Stein » Mon Jul 25, 2005 9:53 am

I think you have a wrong idea, victor.

Unlike other protein antigens, which need to be internalized by APCs and being processed into peptides prior to be presented on MHC molecules, thus the complex MHC:peptide can be recognized by T cell receptor, superantigens are directly bind to T cell receptors without being any processings. They can bind independently to MHC class II molecules and to T cell receptors. This enables them to stimulate very large numbers of T cells.

This mode of stimulation does not prime an adaptive immune response specific for the pathogen. Instead, it causes a massive production of cytokines by CD4+ T cells, the predominant responding population of T cells. These cytokines have two effects on the host: systemic toxicity and suppression of the adaptive immune response.

Superantigens are produced by many different pathogens, including bacteria. mycoplasmas, and viruses, and the responses they provoke are helpful to the pathogens rather than the host.
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Post by victor » Mon Jul 25, 2005 11:20 am

When I saw the picture, superantigens are bind to the variable regio of the T-cell. Oh yes, can you help me to define these words??
Regio Fab
Regio Fc
Constant regio
Variable regio
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Post by iri_black » Mon Jul 25, 2005 11:42 am

Immunoglobulins = polypeptides - two heavy chaines and two light chaines that form a Y shaped molecule.
The sequence of aminoacids in the tips of the "Y" varies= variable region - gives specificity for binding antigen.

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Post by victor » Mon Jul 25, 2005 11:50 am

Can you explain that more detail?? :wink:
What is the component of them and why that some parts are called variable and constant?
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Post by iri_black » Mon Jul 25, 2005 12:44 pm

The variable regions in the tips of the Y are composed of more than 100 aminoacids, both in the light and heavy chaines. An enzyme can cleave the variable region, producing FAB (fragment antigen binding )
The constant region determines the mechanism used to destroy antigen.

At liest that's how i remember it... :?
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Post by Dr.Stein » Tue Jul 26, 2005 10:01 am

Look, I have nice pics for you ;)
I like to explain things with pics much better than words, because pics will tell you and give you more :D

victor wrote:When I saw the picture, superantigens are bind to the variable regio of the T-cell. Oh yes, can you help me to define these words??
Regio Fab
Regio Fc
Constant regio
Variable regio


victor wrote:Can you explain that more detail?? Wink
What is the component of them and why that some parts are called variable and constant?


About B cell receptor (BCR) and immunoglobulin (Ig)
Image

1. Fab region = Fragmen antigen-binding = VL-VH-Cl-CH1, function to bind epitope of specific antigen
2. Fc region = Fragmen crystallizable = CH2-CH3, function to attach on cell surface (of BCR) or to other cells that has receptor for it (of Ig)
3. Constant region = CL-CH1-CH2-CH3, it is so-called because the amino acid sequences is constant
4. Variable region = VL-VH, it is so-called because the amino acid sequence is specific to certain epitope of antigen, means that every BCR or Ig has different variable region

All parts are consisted of amino acids, N terminus on variable region, C terminus on constant region, connected to each other by disulphide bond -S-S-

The structure of T cell receptor (TCR), the region, is somewhat similar to Fab of BCR or Ig (see below):

About superantigen:
Image

The yellow thing is a peptide processed from antigen, whereas the blue one is a superantigen, with no processing it can bind to TCR (variable region) directly and MHC class II independently.

Can you explain me now what's the main difference of antigen and superantigen? ;)
Image

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Post by victor » Wed Jul 27, 2005 11:16 am

From the pic that I saw below....Antigen is bound by both MHC II and T-cell receptor (need processing) while the other pic need no processing to be bound... :wink: (forgive me if I'm wrong... :lol: )
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