Antigen Recognition by T Lymphocytes

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Antigen Recognition by T Lymphocytes
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Antigen Presenting Cell
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T Cell-Antigen Recognition

• Respond to contiguous short amino acid sequences
  in proteins-T Cell Epitopes
• Peptides
• Not Native Protein
• T cells do not bind free peptides
• T Cells Recognize a complex of a peptide fragment
  bound to the membrane proteins of cells- Major
  histocompatibility complex (MHC) molecules

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MHC Molecules

• MHC I
• MHC II
• Physiological function is to present peptides to
  T cells

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Major Histocompatibility Complex Proteins

• Human-HLA (human leukocyte antigen)
• Mouse H-2
• Bovines BoLA
• Equines ELA
• Swine SLA
• OLA, CLA, DLA, FLA

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MHC Class I Molecules
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MHC Class I Molecules

• Present Peptides to CD8 T Cells
• Expressed on ALL Nucleated Cells of the Body

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Recognition of Peptide/MHC I Complex By the T
Cell Antigen Receptor
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MHC Class II Molecules
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MHC Class II Molecules

• Present Peptides to CD4 T Cells
• Expressed on Dendritic Cells, B Cells,
  Macrophages-Professional Antigen Presenting Cells

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Crystal Structure of MHC Class II Molecules
Peptide
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General Characteristic of Peptide-MHC Interactions

• Each MHC class I class II molecule has a single
  peptide binding cleft that can bind many
  different peptides
• Anchor Residues

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Peptide Binding to MHC Molecules via Anchor
Residues
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• Two different Peptides bind the same MHC
• Sequence Motif

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Features of Peptide Binding to MHC Molecules
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Features of Peptide Binding to MHC Molecules
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MHC Polymorphism
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Properties of MHC Molecules and Genes
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Limited Polymorphism in the MHC Genes causes?
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Self MHC Restriction
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Both CD4 and CD8 T cells can recognize antigen
only when presented by a self-MHC molecule on the
membrane of an antigen presenting cellsCD4 T
Cells-Self MHC II-RestrictedCD8 T Cells-Self
MHC I-Restricted
Self MHC Restriction
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(non-self MHC)
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T Cell Antigen Recognition
B Cell Antigen Recognition
Antigen
APC
MHCPeptide
BCR
TCR
B Cell
T Cell
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T Cell Subsets
MHC Class II MHC Class I Peptide Peptide
Recognizes
TCR
TCR
CD4
CD8
CD3
CD3
T Helper Cell
T Cytotoxic Cell