It’s not only protein antigens of course
that are recognized by the immune response.
Most types of molecules
can be recognized.
So let’s look very briefly at
what happens with lipid antigens.
Well again, they can be
processed and presented.
The details are a little bit different
but the overall concept is very similar.
So for example here we have a glycolipid or
lipoprotein antigen, and this can be endocytosed or
phagocytosed just like protein antigens or indeed whole
intact microorganisms can be taken up by the cell.
So here we have the glycolipid or
lipoprotein antigen, and this can be
chewed up by lipases, rather than proteases chewing up proteins.
Lipases can chew up these
particular types of antigen.
Meanwhile in the endoplasmic reticulum,
the CD1 molecule is being produced.
Now this is a molecule that is
very, very similar to MHC Class I.
It’s not an MHC Class I molecule,
but it has a very similar structure.
It’s not identical structure,
but a very similar structure.
And it can bind lipid antigens.
So again it needs to be exported, it needs to
get together with the processed lipid antigen.
So it needs to be exported
from the endoplasmic reticulum.
And then these two vesicles need to get together just as
we saw previously with protein antigen and MHC Class II.
And the lipid antigens can be inserted
into the binding groove of the CD1
molecule which is specialized to bind
to lipid antigens, and then this
will be taken to the cell surface where
this combination of lipid plus CD1
can be presented to αβ T-cells, to
γδ T-cells or indeed to NKT-cells.