Questions and Answers
What are the 3 broad classes of T cells?
Which classes of T cells are CD4?
Which classes of T cells are CD8?
How many antigen binding sites does a T cell receptor have?
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How many hypervariable regions make up the T cell antigen binding site?
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What is the function of the T cell receptor constant regions?
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What 3 processes are responsible for generating T-cell receptor diversity?
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What gene segments make up the α-chain variable region of the T cell receptor?
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What gene segments make up the β-chain variable region of the T cell receptor?
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Are the constant regions of the T cell receptor composed of gene segments?
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What type of antigen do T cells recognize and what type of molecule must the antigen be presented on?
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From what location are the presented antigens for MHC class I derived?
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From what location are the presented antigens for MHC class II derived?
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What type of T cells are activated by MHC class I?
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What type of T cells are activated by MHC class II?
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Which cell types express MHC class I molecules?
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Which cell types express MHC class II molecules?
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Which T cell co-receptor (CD4 or CD8) binds to MHC class I?
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Which T cell co-receptor (CD4 or CD8) binds to MHC class II?
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What is cross-presentation?
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Why is it necessary for dendritic cells to sometimes use cross presentation?
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How many different MHC class I and II molecules does each person have for presenting antigens?
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The MHC genes are the most polymorphic genes in the genome. What does polymorphic mean?
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Why is it beneficial for the human population to have such a large number of different MHC alleles?
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How are only 12 MHC molecules in each person able to present such a broad range of antigens from all of the many pathogens encountered by the body?
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What determines which antigens will bind to a particular MHC molecule?
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What is MHC restriction?
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What is a peptide binding motif?
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Which MHC class I molecules are involved in antigen presentation?
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Which MHC class II molecules are involved in antigen presentation?
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Study Notes
T Cell Overview
- T cells can be classified into three broad categories: Helper, Regulatory, and Cytotoxic.
- Helper and Regulatory T cells express the co-receptor CD4, while Cytotoxic T cells express CD8.
T Cell Receptor (TCR) Structure
- A T cell receptor has a single antigen-binding site.
- The antigen-binding site consists of six hypervariable regions.
- Constant regions of the TCR provide structural support and anchor the receptor to the cell membrane.
- The α-chain variable region is formed from gene segments V and J.
- The β-chain variable region is formed from gene segments V, D, and J.
- Constant regions are not composed of gene segments.
Antigen Recognition and Presentation
- T cells recognize antigens as peptides presented by Major Histocompatibility Complex (MHC) molecules.
- MHC class I presents antigens derived from the cytosol, while MHC class II presents antigens derived from the extracellular environment or endosomal system.
T Cell Activation
- CD8 T cells are activated by MHC class I molecules.
- CD4 T cells are activated by MHC class II molecules.
- MHC class I molecules are expressed by most body cells, which can be infected by intracellular pathogens.
- MHC class II molecules are primarily expressed by professional antigen-presenting cells: dendritic cells, macrophages, and B cells.
Co-receptors and Antigen Presentation
- The CD8 co-receptor binds to MHC class I.
- The CD4 co-receptor binds to MHC class II.
- Cross-presentation enables dendritic cells to present extracellular antigens on MHC class I to activate CD8 T cells even if they are not infected.
Diversity of MHC and T Cells
- Each person has 6 MHC class I molecules and 6 MHC class II molecules, inherited from both parents.
- MHC genes are the most polymorphic in the genome, meaning each gene has many different alleles.
- A large variety of MHC alleles enhances the immune system's ability to present a wide range of antigens, making it less likely for pathogens to evade detection.
MHC Functionality
- MHC molecules exhibit promiscuous binding affinity, allowing them to bind a diverse range of peptide antigens.
- Peptides must have specific anchor residues to bind to a particular MHC molecule, determining which antigens will be presented.
- MHC restriction refers to the specificity of a T cell receptor for both the antigen and the associated MHC molecule.
- The peptide binding motif is characterized by the sequence of anchor residues that interact with MHC molecules.
MHC Class Specificity
- MHC class I molecules involved in antigen presentation include A, B, and C.
- MHC class II molecules involved in antigen presentation include DP, DQ, and DR.
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Test your knowledge on T cell receptors and MHC molecules with these flashcards. Dive into the specifics of T cell classes and their functions, including the roles of CD4 and CD8 cells. Perfect for students studying immunology or related fields.
