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Differential Antigen Processing Pathways
TAP: Transporter associated with Antigen Processingheterodimer
Black proteosome subunits alter catalysis to produce MHC I ready peptides
Assembly of “Loaded” MHC I requires chaperone proteins CalnexinTapasin associates with TAP to help load the peptideERp57 allows for release of the “loaded” MHC I after assembly.
Loading MHC II
Assembly of MHC II: Newly synthesized MHC binds invariant chain (prevents premature peptide binding and helps direct MHC to endocytic compartment via sorting signals). Invariant chain is degraded as the complex passes through the endocytic pathway. CLIP (Class I-associated Invariant Chain Peptide) stays bound in the peptide-binding groove.
A “non-classical” MHC II molecule, HLA-DM, catalyzes the exchange with peptides to be presented. HLA-DM is intracellular only.
Summary of antigen processing.
Only membrane bound—structural analysis tough… why?
Early T-Cell Studies
• Infect mice with lymphocytic choriomeningitis virus (LCMV)
• CTLs generated lysed infected cells• Did not react with free virus particles or
viral peptides• ??????????• Self-restriction of T-cells• Analyze TCRs by antibody
production/binding• TCRs have Variable regions and Constant
regions!!!!!!!!!!!• ISOLATE GENE
Subtractive Hybridization
Why?
98% of gene expression is the same in B and T cells
Rearranged DNA
In Ig superfamilyWhy?
Like Fab
Other TCRs are
Secondary structure?
MHC not required for recognition!More like innate immunity.Important against parasites and some bacteria.
Productive rearrangement for deletes !!
Gene rearrangements yield a functional TCR.
Rearranged genes
Unlike B-cells, T-cells do not undergo somatic mutations.
T-cell receptor Complex: TCR + CD3
and result fromdifferential RNA splicing
Immunoreceptor tyrosine-based activation motif
Ig domains
TCR accessory proteins
Coreceptor interactions
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