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
