Antigen Presenting Cells (APCs)
369
Endogenous
antigen
HLA-DM
MHC II-
invariant
chain
TAP
Proteasome
MHC I
Tapasin
Peptides
MHC class II
MHC class I
Plasma
membrane
Trans-Golgi
network/
Golgi
Endoplasmic
reticulum
Peptides
Endosomes/
lysosomes
Exogenous
antigen
CD1
CD1
CLIP
Lipid
Fig. 5
Antigen processing pathways leading to the generation of MHC class
I-peptide, MHC class II–peptide, and CD1-lipid complexes.
for the regular supply of MHC class I
molecules with peptide antigen. More-
over, TAP is an essential constituent of
a multimolecular peptide–loading com-
plex in the ER that regulates loading of
MHC class I molecules with cognate anti-
genic peptides.
6.1.3
The MHC Class I Loading Complex
Newly synthesized MHC class I heavy
chains (
α
) are stabilized by binding to
the chaperone calnexin until the heavy
chain forms dimers with
β
2
-microglobulin
(
β
2m
).
After
dissociation
of
calnexin,
the chaperone calreticulin allows
α
:
β
2m
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