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Review
. 1999 May;44(5):759-64.
doi: 10.1136/gut.44.5.759.

Mechanisms of immune escape in viral hepatitis

W Rosenberg  1
Affiliations
Review

Mechanisms of immune escape in viral hepatitis

W Rosenberg. Gut. 1999 May.
No abstract available

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Figures

Figure 1
Figure 1
Antigen processing and presentation. T lymphocytes recognise short linear peptides bound to MHC molecules on the surface of antigen presenting cells (APC) through the antigen specific T cell receptor (TCR). Specificity of recognition is determined by a conformational interaction between the peptide binding to the MHC molecule and between the TCR and MHC-peptide antigen complexes. (A) Exogenous antigen processing: CD4+ T cells recognise exogenously derived peptides presented in the antigen binding cleft of class II MHC molecules. Exogenous proteins are taken up into endocytic vesicles which fuse with lysozomes to bring about proteolytic degradation of proteins to peptides and the removal of invariant chain from the antigen binding cleft of MHC class II molecules. Peptides capable of binding to MHC class II molecules occupy the antigen binding cleft and the MHC-peptide complex is then expressed on the cell surface where it can engage antigen specific TCRs co-expressed with co-stimulatory molecules on CD4+ T cells. (B) Endogenous antigen processing: CD8+ T cells recognise peptides generated from endogenously processed proteins, such as viruses, by the proteosome complex. These peptides are transported into the endoplasmic reticulum by the transport associated protein (TAP) complex where they associate with MHC class I heavy chains and β-2 microglobulin. Peptides capable of binding to the antigen binding cleft of class I heavy chains form stabile complexes of heavy chain, β-2-microglobulin and peptide which is then transported to the cell surface where the MHC-peptide complexes can be recognised by antigen specific TCRs on the surface of CD8+ T cells co-expressed with co-stimulatory molecules. The successful presentation of peptides in MHC molecules is dependent on the access of proteases to cleavage sites, the co-location of peptides and MHC molecules, conformational interaction of peptide and MHC to form stable complexes and then cell surface expression of MHC-peptide complexes.
Figure 2
Figure 2
MHC-peptide:TCR interactions and consequences. Peptide interactions with MHC and TCR are represented. (A) MHC binds peptide and presents it to TCR leading to recognition by the T cell and activation. (B) Peptide binds to MHC but a changed TCR contact residue results in loss of recognition by the T cell. (C) Changes in "anchor residues" prevent the peptide from occupying the MHC antigen binding cleft and so the peptide is neither presented nor recognised. (D) Antagonism. The peptide binds to the MHC molecule and engages the TCR but, because of a subtle change in a TCR contact residue, the T cell is not activated but antagonised.
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