Voie d'immunisation et séquence d'administration de l ... - TEL

tel-00827710, version 1 - 29 May 2013
(b) Presentation of extracellular antigens on MHC-II
While MHC-I molecules are expressed by all nucleated cells, only few cell types express
MHC-II molecules (B cells, thymic epithelial cells, macrophages and DCs) and can thus
present extracellular antigens to CD4 + T cells.
Following engulfment, the exogenous antigen is partially degraded and the resulting peptides
are transferred to the MHC-II compartment where they compete with the Class II associated
invariant chain peptide (CLIP) for binding to the pre-assembled MHC-II molecule. Then
MHC molecules loaded with peptides are stabilized and transported to the cell surface
(Figure 3, pathway 1, orange arrows). Degradation of the engulfed antigen is dependent on
the acidic pH in endosomes and phagosomes, which allows the activation of lysosomal
proteases required for the digestion of antigens and their loading on MHC-II molecules. Of
note, endogenous peptides originating from endosomal proteins, proteins from plasma
membrane, or from cytosolic components transferred into endosomes via autophagy can also
be presented on MHC-II (Buckwalter and Albert, 2009) (Figure 3, pathway 2, green
arrows).
Figure 3. Generation of MHC-II-peptide complexes from endogenous and exogenous antigen.
The pathway 1 (orange arrows) represents the presentation of exogenous antigen on MHC-II. The
pathway 2 (green arrows) corresponds to the presentation of endogenous antigen on MHC-II
molecules. Figure from Buckwalter et al., 2009.
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