Repertoire Selection

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Repertoire Selection

• February 28, 2007
• Penny Morel
• 4-0343, morel_at_pitt.edu

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Figure 7-14
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TCR Overlay MHC
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Nature of positive selecting ligands

• Antagonist peptides
• Low affinity peptides
• Low density peptides
• ?common structural features
• Many experimental approaches have been tried
  Synthetic altered peptide ligands and FTOC,
  isolation of naturally occurring peptides

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SIINFEKL peptide OT1 Tg
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Identification of naturally presented peptides
for positive selection OT1 TCR Tg T cells
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Nat Immunol. 2005 6143-51
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SH Stationary, hi Ca SL Stationary, lo
Ca ML Motile, lo Ca
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Summary of results
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Experimental methods to study negative selection

• Anti-CD3 in vivo kills DP thymocytes
• Endogenous superantigen deletes T cells with
  specific Vb usage
• TCR Tg mouse treated with peptide in vivo or in
  vitro (Mature T cells stimulated at high
  frequency produce cytokines that induce
  nonspecific death of DP thymocytes)
• TCR Tg with endogenous ligand - many different
  models

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TCR b transgenic specific for MCC peptide
J Immunol. 1999 163689-98.
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Mice express fusion protein HEL/MCC
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Negative Selection TCR tg mouse expressing HY
recognizing TCR. In male mice this T cell is
deleted. In absence of Bim there is no
deletion. Apoptosis of negatively selected T
cells requires this pro-apoptotic Bcl-2
family member.
CD4
Nature 415922, 2002
CD8
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CD4 CD25 CD45RBlo CD62L suppressor T cells

• Thymus dependent
• 5-10 of peripheral CD4 T cells
• Suppress activation of CD4 CD25- cells in vitro
  by inhibiting IL-2 production
• Suppression requires cell/cell contact

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Thymectomized mice develop autoimmunity
J Exp Med. 1996 184387-96
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Development of CD25 T cells
J Exp Med. 1996 184387-96
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Develop in Thymus
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Regulatory T cells
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FoxP3

• Forkhead family of transcription factors
• Mice with FoxP3 mutation (scurfy mouse) develop
  fatal autoimmune syndrome
• Human disease IPEX - fatal autoimmune syndrome -
  FoxP3 mutation (X-linked)
• Specific for reg T cells
• Gene targets and function unknown

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FoxP3 and Treg
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Foxp3 -/- mice have no suppressor cells Nature
Immunol. 4330, 2003
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FoxP3 reporter mice - GFP inserted into FoxP3
gene Used to follow development of Treg - mainly
in medulla Treg development requires MHC/TCR
engagement
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Development of Treg over time JEM
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DBA/2 mice express sAg in thymus that result in
deletion of V?3, V?5 and V?6 In MHC0 - DBA/2 only
thymic epithelium expresses sAg (no deletion
expanded Treg) In B10D2 - DBA/2 both DC and TE
express sAg (deletion no Treg expansion
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Other Factors necessary for Treg development

• IL-2 - IL2 -/-, IL2R -/- mice all develop
  autoimmunity
• TGF-?
• CD28
• Some of these factors are necessary for
  maintenance also