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This is a
talk on antigen processing
and presentation, and
in particular how it's
regulated by innate immune signals.
And it's given by Colin Watts
from the University of Dundee.
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Antigen presentation refers to
the display of short process
peptides on so-called MHC,
or major histocompatibility
complex molecules.
Seen here is a class I MHC molecule
with the short 8-residue peptide
found in a peptide binding groove.
Class I MHC molecules generally
have peptides between 8
and 10 amino acid residues.
Whereas class II MHC molecules
display considerably longer
peptides due to a more open
ended peptide-binding groove.
It's the recognition
of these peptide MHC
complexes by the T
cell antigen receptors
that initiates most
immune responses.
We can distinguish the two
classes of MHC molecule
by the types of
peptide they present.
As simply diagrammed here, class
I MHC molecules display peptides
which are derived
from intracellular,
i.e. cytosolic or nuclear proteins,
which as we'll see in a moment,
become loaded in the
endoplasmic reticulum
and transported to
the cell surface where
they're recognized by CD8 T cells.
Usually the outcome
of recognition is
killing, for example, of the
virally infected or a tumor cells.
In contrast, class II MHC molecules
capture and display peptides
derived from exogenous
proteins, i.e. proteins taken up
into the cell by one or
more forms of endocytosis,
for example, bacterial
toxins like tetanus toxin.
Here the endocytic pathway acts
as the site for peptide loading.
And then following transport
to the cell's surface,
the CD4 T cell can perform various
functions, for example can help
a B lymphocyte to differentiate and become
an antibody producing cell.
The two T cells seen in this slide
are so-called effector T cells.
They have previously
been activated and are
primed to perform an effector
function, which was just described.
But these T cells must have already
been activated by a different type
of antigen presenting cell.
And it's clear, and as well
discussed elsewhere in the series,
that dendritic cells are uniquely
able to prime naive T cells.
