immunology12 - Immunology 12-Endogenous Pathway of Antigen...

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Immunology 12-Endogenous Pathway of Antigen Processing and Presentation Variable region of Ab is similar to variable region of CR; both use the variable regions to form an antigen binding site TCR does not have a Fc region TCR is similar to an Fab fragment of antibody Y:δ T cell receptors have different antigen recognition properties from the a:B T cell receptors Stalk segment has a cysteine residue that forms the interchain disulfide bond; short stalk is homologous to the Ig hinge region; alpha chain has 2 positive residues in the hydrophobic domain, the B chain only has 1 In the C alpha domain the intramolecular disulfide bond joins a B strand to this segment of alpha helix Interface between the C and V domains of both T-cell receptor chains is more extensive than in most Abs The C alpha domain doesn’t fold into a typical Ig domain; the face of the domain away from the C beta domain is mainly composed of irregular strands of polypeptide rather than B sheet; sugar groups on C alpha make hydrogen bonds with C beta domain Differ from B cell receptor: has only ONE Ag binding site and TCRs are never secreted 1 type of T-cell receptor on each T-cell TCR: alpha chain and beta chain joined by disulfide bridge; extremely short cytoplasmic tail so it must use co-receptors; variable and constant regions; variable region has surface that recognizes 3D conformation of antigen but is different from B- cell recognition TCR antigen recognition T cells (via T cell receptors) only recognize foreign antigens displayed on the surface of the body’s own cells Respond to short continuous amino acid sequences; often buried within the native structure T cell interacts with the ligand by making contacts with both the MHC molecule and the antigen peptide Antigen is displayed as peptide fragments bound to MHC molecules Peptides can stimulate T cells only when bound by MHC—the phenomenom is called MHC restriction (limiting) Different MHC molecules (encoded by different genes as well as by different alleles of genes) have specific differences in what subset of peptides they are able to present to T cells Only linear peptides! No globular proteins, phenols etc MHC restriction T cell recognizes a specific peptide and MHC combination; it won’t recognize the same peptide on a different MHC molecule or a different peptide on hte same MHC molecule Recognizes surface of peptide/MHC molecule MHCI/MHCII
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MHC molecules have peptide binding clefts Class I: binding cleft formed by alpha1/alpha2 subunits; floor formed by B2- microglobulin; alpha chain is noncovalently associated with the B2 unit; alpha 3 and B2 closely resemble Ig like domains in their folded structure; the sides of the cleft are formed by the inner faces of the 2 alpha helices; the B pleated sheet formed by the pairing of alpha 1 and alpha 2 creates the floor of the celft Class II: bigger opening on binding cleft that MHC I; important for binding
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immunology12 - Immunology 12-Endogenous Pathway of Antigen...

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