What is antigen presentation

1
What is antigen presentation? Degradation of
peptides so that they can be presented to T
cells by MHC Class I or Class II molecules on
the surface of APCs
2
Class I MHC molecules present to T
cells Endogenous peptides- viral proteins,
tumor proteins, etc.- that are processed in
the cytoplasm of the cell Class II MHC
molecules present to T cells Exogenous
antigens- internalized and processed by a
different pathway
3
Self-MHC restriction of T cells (1970s)
By TH cells
p. 206
4
By Tc (cytotoxic T) cells
p. 207
5
Role of antigen-presenting cells
Antigen must be processed (p. 208)
6
What is an antigen-presenting cell (APC)? Three
kinds of professional APCs Dendritic cells
(always express high levels of MHC Class
II) Macrophages- must be activated to express
high MHC Class II and B7 B cells- always
express high MHC Class II but must be stimulated
to express B7
7
To review, two pathways for processing
antigen In one pathway, antigens are processed
and associate with Class II molecules In the
other, antigens are processed through different
cellular compartments and associate with Class
I Various receptor and transporter proteins
have been elucidated
8
Summary of the pathways
p. 216
9
These pathways produce peptide (protein) antigens
What about nonpeptide antigens? Another
molecule on APCs, CD1, resembles MHC Class
I These molecules can present lipids and
glyco- lipids like those on bacterial
surfaces Not clear when, or how, this pathway
is exploited
10
Recent studies of CD1 indicate that CD1
presents lipid and glycolipid antigens derived
from bacteria for specific recognition by T
cells CD1 resembles MHC I and associates with
beta-2-microglobulin Five genes encode human
CD1 molecules May be an innate mechanism