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antigen presentation 53 antigen presentation
C
Presentation of MHC histocompatibility antigen HLA-B270S complexes
with nonapeptide ARG-ARG-ILE-LYS-ALA-ILE-THR-LEU-LYS. The
C terminal amino acid of the antigen-binding domain is protected by an
N-methyl group. Three water molecules bridge the binding of the peptide
to the histocompatibility protein.
endoplasmic reticulum. Following cleavage of the invariant
chain, DM molecules remove a tiny piece of invariant
chain from the MHC molecules’ peptide-binding grooves.
Following complexing of extracellular-derived peptide with
Class I
TGN
Golgi
Endoplasmic
reticulum
N
C
N
αβli
the class II MHC molecule, the MHC–peptide complex
is transported to the cell surface where presentation to
CD4 + cells occurs. Proteins in the cytosol, such as those
derived from viruses, may be processed through the class
I MHC route of antigen presentation. The multiprotein
complex in the cytoplasm, known as the proteasome, leads
to proteolytic degradation of proteins in the cytoplasm
to yield many of the peptides that are presented by class
I MHC molecules. TAP molecules transport peptides
from the cytoplasm to the endoplasmic reticulum where
they interact and bind to class I MHC dimeric molecules.
Once the class I MHC molecules have become stabilized
through peptide binding, the complex leaves the endoplasmic
reticulum, entering the Golgi apparatus en route to the
surface of the cell. Thus, mechanisms are provided through
MHC-restricted antigen presentation to guarantee that
peptides derived from extracellular microbial proteins can
be presented by class II MHC molecules to CD4 + helper T
cells and that peptides derived from intracellular microbes
can be presented by class I MHC molecules to CD8 + cytotoxic
T lymphocytes. The generation of microbial peptides
produced through antigen processing to combine with self
Class II
LFA-3
Early
endosome
Processing pathways for class II-restricted antigen presentation.
MHC
Class II
APC
(macrophage or dendritic cell)
αβ
ICAM-1
Ag
peptide
Late
endosome
Lysosome
LFA-1
Antigen presentation.
TCR
CD4 CD2
T cell
A