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
--
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Philip Fung
Sid Richardson College
Rice University GO OWLS!
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