MHC-I viral Ag presentation

John Richard Seavitt jrseavit at artsci.wustl.edu
Thu May 7 12:54:50 EST 1998

On 6 May 1998, Victor DeFilippis wrote:

> A potentially stupid question follows.  How can Ag's be presented to CD8+
> cells (via MHC-I) for viruses which never infect professional APC's?  It's
> my (admittedly naive) impression that in order for peptides to be presented
> on MHC-I molecules the proteins need to be synthesized in the cytoplasm.
> Does this mean that highly tissue specific viruses that totally avoid
> replication in APC's never have a CTL response directed toward them?  

Short answer:  the important feature of "professional APC"s is that they
phagocytose material, digest it with acid proteases, and present some of
the resulting peptides on MHC class II molecules.  MHC class I molecules,
however, are loaded with cytoplasmically-derived peptides from within the
same cell, as you suggest.  Unlike MHC class II and APCs, however,
essentially all of your cells express the machinery to present MHC class
I.  It's useful to think of it largely as a two-pronged system:  CD4 T
cells looking at APCs, which present material from bacteria and other
cellular pathogens, and CD8 T cells looking at (nearly) all cells, which
present a sampling of their cytoplasmic proteins, including any that may
be derived from viral pathogens.


"Seek enlightenment:  Thwack somebody upside the head with a big stick."

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