🚀 go-pugleaf

In article <7vub1d$bm2$1@news.net.uni-c.dk>,
Morten Lindow <lindow@mdb.ku.dk> wrote:
>
>The question is: What happens if a virus doesn't infect APCs? Say it is
>specific for epithelial cells.  How does viral peptides  then end up on
>class I molecules on APCs?  I figure that APCs could phagocytise free viral
>particles, but wouldn't that result in presentation on class II MHCs?

An excellent question, actually.  The answer is not particularly
intuitive, and certainly won't be in your textbook, because it was just
published earlier this year:

Nature 1999 Mar 4;398(6722):77-80 
Cytotoxic T-cell immunity to virus-infected non-haematopoietic cells
requires presentation of exogenous antigen.
Sigal LJ, Crotty S, Andino R, Rock KL

The short explanation is that APC can phagocytose particulate antigen and
present it on MHC class I.  The molecular details of this aren't clear,
but the observation is.

Ian 
-- 
    Ian York   (iayork@panix.com)  <http://www.panix.com/~iayork/>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England

I may be wrong on this one, but I'm pretty sure that all (or nearly all)
nucleated
cells have MHC Is, right? and MHC Is present peptides processed in the
cytosol, right? That's how the viral peptides are presented on MHC Is... the
virus infects the cells, and starts transcribing its proteins. Then the cell,
by way
of the proteasome, processes those cyosolic proteins. Any cell infected by a
virus can present viral antigenic peptides on its MHC Is. As long as there is a

T-cell to be activated by it, it can happen. at least according to my textbook
(Kuby, 1997)

Activation doesn't have to happen in the lymphoid tissue, either. However, most

of it does happen there, at least from what I understand, but there are T cells
in
the bloodstream that can come in contact with the MHC Is of other cells in the
body. But you're right. epithelial viral infections, like HPV, often do not
elicit as
large of an immune response because it is relatively difficult to access, in
terms
of the lymphocytes abilities to "reach" MHCs in those areas.

One side note, there are also certain superantigens (certain proteins produced
by
certain viruses and bacteria) which serve to activate T-cells w/o an antigenic
peptide in Class II MHCs, but that's something else... But a virus can cause
T-cell activation by that route.

Phil

Morten Lindow wrote:

> I have got a question about the activation of naive T-cells by viral
> antigens.
>
> According to my textbook (Janeway-Travers) activation of CD8+ T-cells
> require recognition of MHC class I loaded with viral antigen and
> costimulation through CD28 by B7.1 or B7.2 on an APC. All this takes place
> in lymphoid tissue.
>
> The question is: What happens if a virus doesn't infect APCs? Say it is
> specific for epithelial cells.  How does viral peptides  then end up on
> class I molecules on APCs?  I figure that APCs could phagocytise free viral
> particles, but wouldn't that result in presentation on class II MHCs?
>
> Is there a flaw in my understanding? Any ideas and comments would be very
> welcome.
>
> Regards,
>
> Morten Lindow
> Copenhagen, Denmark

--
+++++++++++++++++++++++++++++++++++++++++++++
Philip Fung
Sid Richardson College
Rice University   GO OWLS!
+++++++++++++++++++++++++++++++++++++++++++++
Let us so live that when we come to die even the undertaker will be sorry.
- Mark Twain

that's correct, epithelial cells can express MHC

Philip Fung <phfung@NOSPAM4ME!owlnet.rice.edu> wrote in message
news:7vvlbb$n18$1@joe.rice.edu...
| I may be wrong on this one, but I'm pretty sure that all (or nearly all)
| nucleated
| cells have MHC Is, right? and MHC Is present peptides processed in the
| cytosol, right? That's how the viral peptides are presented on MHC Is...
the
| virus infects the cells, and starts transcribing its proteins. Then the
cell,
| by way
| of the proteasome, processes those cyosolic proteins. Any cell infected by
a
| virus can present viral antigenic peptides on its MHC Is. As long as there
is a
|
| T-cell to be activated by it, it can happen. at least according to my
textbook
| (Kuby, 1997)
|
| Activation doesn't have to happen in the lymphoid tissue, either. However,
most
|
| of it does happen there, at least from what I understand, but there are T
cells
| in
| the bloodstream that can come in contact with the MHC Is of other cells in
the
| body. But you're right. epithelial viral infections, like HPV, often do
not
| elicit as
| large of an immune response because it is relatively difficult to access,
in
| terms
| of the lymphocytes abilities to "reach" MHCs in those areas.
|
| One side note, there are also certain superantigens (certain proteins
produced
| by
| certain viruses and bacteria) which serve to activate T-cells w/o an
antigenic
| peptide in Class II MHCs, but that's something else... But a virus can
cause
| T-cell activation by that route.
|
| Phil
|
| Morten Lindow wrote:
|
| > I have got a question about the activation of naive T-cells by viral
| > antigens.
| >
| > According to my textbook (Janeway-Travers) activation of CD8+ T-cells
| > require recognition of MHC class I loaded with viral antigen and
| > costimulation through CD28 by B7.1 or B7.2 on an APC. All this takes
place
| > in lymphoid tissue.
| >
| > The question is: What happens if a virus doesn't infect APCs? Say it is
| > specific for epithelial cells.  How does viral peptides  then end up on
| > class I molecules on APCs?  I figure that APCs could phagocytise free
viral
| > particles, but wouldn't that result in presentation on class II MHCs?
| >
| > Is there a flaw in my understanding? Any ideas and comments would be
very
| > welcome.
| >
| > Regards,
| >
| > Morten Lindow
| > Copenhagen, Denmark
|
| --
| +++++++++++++++++++++++++++++++++++++++++++++
| Philip Fung
| Sid Richardson College
| Rice University   GO OWLS!
| +++++++++++++++++++++++++++++++++++++++++++++
| Let us so live that when we come to die even the undertaker will be sorry.
| - Mark Twain
|
|

I think that only bacteria produce proteins that can act as superantigens, toxic
shock toxin from Staph. aureus for example.  At least I have never heard of any
from viruses.

Philip Fung wrote:

> I may be wrong on this one, but I'm pretty sure that all (or nearly all)
> nucleated
> cells have MHC Is, right? and MHC Is present peptides processed in the
> cytosol, right? That's how the viral peptides are presented on MHC Is... the
> virus infects the cells, and starts transcribing its proteins. Then the cell,
> by way
> of the proteasome, processes those cyosolic proteins. Any cell infected by a
> virus can present viral antigenic peptides on its MHC Is. As long as there is a
>
> T-cell to be activated by it, it can happen. at least according to my textbook
> (Kuby, 1997)
>
> Activation doesn't have to happen in the lymphoid tissue, either. However, most
>
> of it does happen there, at least from what I understand, but there are T cells
> in
> the bloodstream that can come in contact with the MHC Is of other cells in the
> body. But you're right. epithelial viral infections, like HPV, often do not
> elicit as
> large of an immune response because it is relatively difficult to access, in
> terms
> of the lymphocytes abilities to "reach" MHCs in those areas.
>
> One side note, there are also certain superantigens (certain proteins produced
> by
> certain viruses and bacteria) which serve to activate T-cells w/o an antigenic
> peptide in Class II MHCs, but that's something else... But a virus can cause
> T-cell activation by that route.
>
> Phil
>
> Morten Lindow wrote:
>
> > I have got a question about the activation of naive T-cells by viral
> > antigens.
> >
> > According to my textbook (Janeway-Travers) activation of CD8+ T-cells
> > require recognition of MHC class I loaded with viral antigen and
> > costimulation through CD28 by B7.1 or B7.2 on an APC. All this takes place
> > in lymphoid tissue.
> >
> > The question is: What happens if a virus doesn't infect APCs? Say it is
> > specific for epithelial cells.  How does viral peptides  then end up on
> > class I molecules on APCs?  I figure that APCs could phagocytise free viral
> > particles, but wouldn't that result in presentation on class II MHCs?
> >
> > Is there a flaw in my understanding? Any ideas and comments would be very
> > welcome.
> >
> > Regards,
> >
> > Morten Lindow
> > Copenhagen, Denmark
>
> --
> +++++++++++++++++++++++++++++++++++++++++++++
> Philip Fung
> Sid Richardson College
> Rice University   GO OWLS!
> +++++++++++++++++++++++++++++++++++++++++++++
> Let us so live that when we come to die even the undertaker will be sorry.
> - Mark Twain

Might be. I'm just regurgitating what read in my book and what I was
told in class.  :-)

Tammy Ferguson wrote:

> I think that only bacteria produce proteins that can act as superantigens, toxic
> shock toxin from Staph. aureus for example.  At least I have never heard of any
> from viruses.
>
>
> >
> > One side note, there are also certain superantigens (certain proteins produced
> > by
> > certain viruses and bacteria) which serve to activate T-cells w/o an antigenic
> > peptide in Class II MHCs, but that's something else... But a virus can cause
> > T-cell activation by that route.
> >

--
+++++++++++++++++++++++++++++++++++++++++++++
Philip Fung
Sid Richardson College
Rice University   GO OWLS!
phfung@rice.edu
philfung@aol.com
http://www.owlnet.rice.edu/~phfung/
+++++++++++++++++++++++++++++++++++++++++++++
Let us so live that when we come to die even the undertaker will be sorry.
- Mark Twain

In article <3825E719.1D99B0B5@hsc.vcu.edu>,
Tammy Ferguson  <tjfergus@hsc.vcu.edu> wrote:
>I think that only bacteria produce proteins that can act as superantigens, toxic
>shock toxin from Staph. aureus for example.  At least I have never heard of any
>from viruses.

There are also viral superantigens.  Superantigens have been identified in
the murine retroviruses MMTV (mouse mammary tumor virus) and MuLV (murine
leukemia virus), and there is evidence that HIV may also produce a
superantigen.  I believe that the murine retroviral superantigens are
membrane-bound, but may have secreted forms as well.

Ken Frauwirth


-- 
Ken Frauwirth (MiSTie #33025)  kfrauwir@midway.uchicago.edu
Abramson Cancer Research Institute
University of Pennsylvania
http://mail.med.upenn.edu/~kfrauwir

The viral proteins expressed on infected cells are those produced
endogenously.  Virtually all nucleated cells express class I molecules
and have the proteasome pathway for the production of peptide
fragments of 8-13 amino acids which will bind to the class I
molecules.  These are then expressed on the surface of the cell for
interaction with the T cell receptor of CD8+ T cells.  When antigen is
expressed on class I molecules the convention is to call the cell a
target cell rather than an APC.

On Fri, 5 Nov 1999 11:20:07 +0100, "Morten Lindow" <lindow@mdb.ku.dk>
wrote:

>I have got a question about the activation of naive T-cells by viral
>antigens.
>
>According to my textbook (Janeway-Travers) activation of CD8+ T-cells
>require recognition of MHC class I loaded with viral antigen and
>costimulation through CD28 by B7.1 or B7.2 on an APC. All this takes place
>in lymphoid tissue.
>
>The question is: What happens if a virus doesn't infect APCs? Say it is
>specific for epithelial cells.  How does viral peptides  then end up on
>class I molecules on APCs?  I figure that APCs could phagocytise free viral
>particles, but wouldn't that result in presentation on class II MHCs?
>
>Is there a flaw in my understanding? Any ideas and comments would be very
>welcome.
>
>
>Regards,
>
>Morten Lindow
>Copenhagen, Denmark
>
>

I did receive a message stating that "depending on who I spoke with" some believe that
HIV-1 is capable of producing them.  I haven't checked it out yet. = )

Philip Fung wrote:

> Might be. I'm just regurgitating what read in my book and what I was
> told in class.  :-)
>
> Tammy Ferguson wrote:
>
> > I think that only bacteria produce proteins that can act as superantigens, toxic
> > shock toxin from Staph. aureus for example.  At least I have never heard of any
> > from viruses.
> >
> >
> > >
> > > One side note, there are also certain superantigens (certain proteins produced
> > > by
> > > certain viruses and bacteria) which serve to activate T-cells w/o an antigenic
> > > peptide in Class II MHCs, but that's something else... But a virus can cause
> > > T-cell activation by that route.
> > >
>
> --
> +++++++++++++++++++++++++++++++++++++++++++++
> Philip Fung
> Sid Richardson College
> Rice University   GO OWLS!
> phfung@rice.edu
> philfung@aol.com
> http://www.owlnet.rice.edu/~phfung/
> +++++++++++++++++++++++++++++++++++++++++++++
> Let us so live that when we come to die even the undertaker will be sorry.
> - Mark Twain