T Cells: Receptors, MHC, and Antigen Recognition Flashcards
T cells are defined by _______
T cell receptors (TCRs)
What do T cell receptors primarily bind?
Polypeptides
T/F T cell receptors are secreted by T cells
False, they are expressed on the cell surface, never secreted
What are T cell receptors similar in structure to?
Immunoglobulins
What does the T cell receptors interact with?
MHC presented antigen
T/F T cell receptors are incidence detectors
True
T/F T cell receptors have an effector functioin
False, they have no effector function
T/F T cell receptors are able to recognize antigens in isolation
False, antigens not recognized in isolation, needs an MHC
What are the two classes of T cell receptor?
- alpha:beta T cells
2. gamma:delta T cells
Which t cell receptors is considered the ‘classic’ t cell?
alpha:beta T cells
Which t cell receptor is not involved in the classic adaptive immunity?
gamma:delta T cells
Which T cell receptor is part of adaptive immunity?
alpha:beta T cells
Which T cell receptor is common in circulation but not tissues?
alpha:beta T cells
Which T cell receptor is common in tissues but not circulation?
gamma:delta T cells
Which T cell receptor monitors tissue health?
gamma:delta T cells
Which T cells develop and mature in the thymus?
alpha:beta T cells
Which T cells develop but do not mature in the thymus?
gamma:delta T cells
Which T cells undergo both positive and negative selection in the thymus?
alpha:beta T cells
Which T cells undergo limited positive and negative selection?
gamma:delta T cells
Which T cells only have one class?
gamma:delta T cells
T/F T cells only express one type of receptor, never both
True
T/F Delta chain genes are embedded within the alpha chain genes
True
T/F TCR genes undergo rearrangement
True
What DNA segments are contained within the alpha chain to allow for junctional diversity?
V, J, C segments
What DNA chains are contained within the Beta chain to allow for junctional diversity?
V, J, D, C segments
Each chain has 3 what?
Hypervariable / complementarity-determing regions
Rearrangement of the TCR genes is done by what?
RAG 1/2 complexes
TCRs require what for signal transduction?
CD3 Complex
What does CD3 complex mediate?
TCR Signaling
Plasma membrane TCR expression does not occur without _________
The CD3 complex
What presents antigens to TCRs?
Major Histocompatibililty Complexes
What are the steps of MHC presenting an antigen to TCRs?
- Pathogen protein in cell
- Antigen processing by breakdown of protein
- Presentation of peptide by MHC molecule
- Recognition of antigen MHC complex by T cell receptor
What are the two classes of Major Histocompatibility complex?
MHC Class I
MHC Class II
How many cells express some form of MHC
Nearly all cells
T/F MHC class I is expressed on almost every cell of your body
True
MHC class II is used primarily it which typ of cell?
Antigen presenting cell
T/F MHC class I has alpha chain and Beta2 microglobulin
True
T/F MHC class II has alpha and beta chains
True
Which MHC does ER antigen loading?
Class I
Which MHC does Vesicular ER loading?
Class II
MHC class one has which type of Co-receptor?
CD8
MHC class 2 binds with which type of Co-receptor?
CD4
Both MHC classes bind what for TCR presentation?
peptides
MHC is also referred to as what?
Human Leukocyte Antigen Complex (HLA)
What is the general process of Antigen presentation for MHC I?
- Intracellular antigen
- Antigen Processing Peptides in a proteasome
- Peptide transport into ER
- Peptide binding by MHC class I
- MHC class I presents peptide at cell surface
What is the general process of antigen presentation for MHC Class II?
- Extracellular Antigen
- undergoes phagocytosis
- Peptide Production in phagolysosome
- Peptide Binding by MHC class II
- MHC class II presents peptide at cell surface
What major class of cells does not have MHC?
Erythrocytes
What are the steps of Antigen loading of MHC I in the ER?
- Class I heavy chain is stabilized by calnexin until Beta2-microglobulin binds
- Calnexin is released. The heterodiver of class I heavy chain and Beta2m forms the peptide-loading complex with calreticulin, tapasin, TAP, and ERp57
- A peptide Delivered by TAP binds to the class I heavy chain forming the mataure MHC class I molecule
- The class I molecule dissociates from the peptide-loading complex, and is exported from the endoplasmic reticulum
How large are the intracellular peptides that are cleaved by proteasomes and whose fragments are bound by MHC I?
8-10 residues
Prior to expression in MHC class I, what happens to the peptides?
They are trimmed
What does MHC I presentation of Intracellular peptides allow for?
Detection of an intracellular infection
Where is MHC class I produced?
He said in the Endoplasmic reticulum
What presents most endocytosed antigens?
MHC II
Cross presentation of an endocytosed antigen is particularly important in what?
Naive CD8 T cell activation
List the steps of MHC class II antigen loading into vesicles
- An antigen is taken up from the extracellular space into intracellular vesicles
- In early endosomes of neutral pH, endosomal proteases are inactive
- Acidification of the vesicles activates proteases to degrade antigen into peptide fragments
- Vesicles Containing Peptides fuse with vesicles containing MHC II molecules
What prevents MHC class II from self antigen presentation?
CLIP
List the steps of how CLIP prevents Self Antigen Presentation
- Invariant chain blocks binding of peptides to MHC II molecules in the ER
- In vesicles invariant chain is cleaved, leaving the CLIP fragment bound
- CLIP blocks binding of peptides to MHC class II in vesicles
- HLA-DM facilitates release of CLIP, allowing peptides to bind
What does CLIP stand for?
Class II-associated invariant chain peptide
What dictates MHC specificity?
Co-receptors
_____ binds the alpha3 domain of MHC class I
CD8
______ binds the Beta2 domain of MHC class II
CD4
CD8 only binds what?
MHC I
CD4 only binds _______
MHC II
What are the different types of Effector T cells?
- CD8 Cytotoxic T cells
- CD4 Th1 cells
- CH4 Th2 cells
- CD4 Th17 cells
- Tfh cells
- CD4 regulatory T cells
What are the main functions in the adaptive immune response of CD8 cytotoxic t cells?
Kill virus-infected cells
What are the Pathogens targeted by CD8 cytotoxic T cells?
- Viruses
- Influenza
- Rabies
- Vaccinia
- Some intracellular bacteria
What are the the main functions of CD4 Th1 cells within the adaptive immune response?
- Activate infected macrophages
- Provide help to B cells for antibody production
What are the pathogens targeted by CD4 Th1 cells?
- Microbes that persist in macrophage vesicles
- Mycobacteria
- Listeria
- Leishmania Donovani
- Pneumocystis carinii
- Extracellular Bacteria
What are the main functions within the adaptive immune response of CD4 Th2 cells?
-Provide help to B cells for antibody production, especially switching to IgE
What are the pathogens targeted by CD4 Th2 cells?
Helminth Parasites
What are the main functions within the adaptive immune system of CD4 Th17 cells?
- Enhance neutrophil response
- Promote Barrier Integrity
- Skin
- Intestine
What are the pathogens targeted by CD4 Th17 cells?
- Klebsiella pneumoniae
- Fungi
- Candida Albicans
What are the main functions within the adaptive immune system of Tfh cells?
- B cell help
- Isotype switching
- Antibody production
What are the pathogens targeted by Tfh cells?
All types
What are the main functions of CD4 regulatory T cells within the adaptive immune system?
Suppress T cell responses
List the Different Human MHC class I isotypes
- HLA-A
- HLA-B
- HLA-C
- HLA-E
- HLA-F
- HLA-G
List the different human MHC class II isotypes
- HLA-DM
- HLA-DO
- HLA-DP
- HLA-DQ
- HLA-DR
What cells do not express MHC Class II?
- Neutrophils
- Erythrocytes
- Liver Hepatocytes
- Kidney epithelium
- Brain