B-V MHC:Ag presentation Flashcards
Which cells have MHC Type I?
All cells except red blood cells
Which cells have MHC Type II?
Antigen presenting cells
Which MHC:peptide complex interacts with CD4?
MHC Type II
Which MHC:peptide complexes interacts with CD8?
MHC Type I
Describe the structure of MHC Type I
Three alpha domains; one transmembrane and two forming the peptide binding cleft. One beta-microglobulin
Describe the structure of MHC Type II
Two alpha and two beta domains, one of each transmembrane and one of each forming the peptide binding cleft
Describe the peptide binding characteristics of MHC Type I
Binds shorter peptides, by hydrogen bonds at the the ends of the groove. Causes the middle of peptide to bulge out of the MHC molecule
Describe the peptide binding characteristics of MHC Type II
Binds longer peptides, by hydrogen bonds along the entirety of the binding cleft.
Describe the endogenous pathway of antigen presentation
- Cytosolic protein gets ubiquinated
- The protein gets chopped to pieces in the proteosome
- TAP transports the small peptides from cytosol to ER lumen
- They are placed on MHC (Class I)
- MHC Class I is transported to the surface
Describe the exogenous pathway of antigen presentation
- Antigen is taken up by endocytosis
- It is degraded in the lysosome
- MHC Class II sits in ER, with invariant chain that stabilize
- CLIP removes invariant chain and epitope placed on MHC
- It’s transported to the surface and presented
What is a fundamental requirement for T-cell receptors (TCRs) to recognize antigens?
TCRs cannot recognize native antigens; the antigens need to be processed and displayed by Antigen-Presenting Cells (APCs). Furthermore, there needs to be an interaction between the TCR and the MHC molecule which is displaying the processed protein
On which cells are MHC Class I molecules found, and on which cells are MHC Class II molecules mainly expressed?
MHC Class I molecules are found on all cells except blood cells. MHC Class II molecules are mainly found on professional APCs (Antigen-Presenting Cells), but can also be found on some atypical cells.
How do MHC Class I and Class II molecules differ in the typical length of the peptides they bind?
MHC Class I typically binds shorter peptides that are 8-10 amino acids in length. MHC Class II can bind longer peptides, ranging from 13-18 amino acids.
What role do anchor residues play in the binding of peptides to MHC Class I molecules?
MHC Class I molecules bind peptides using structurally related anchor residues located at the C and N ends of the peptide. These anchor residues create tight bonds at the ends of the peptide-binding groove.
How does the binding of peptides to MHC Class II molecules differ from the binding of peptides to MHC Class I?
Peptides bound to MHC Class I are tightly bound at the ends of the groove but not tightly bound in the middle, causing the peptide to bulge out of the MHC molecule. In contrast, peptides bound to MHC Class II have interactions along the groove, resulting in no bulge.
Describe the key steps in the Class I antigen presentation pathway
The Class I antigen presentation pathway begins with cytosolic proteins or endogenous antigens, which can originate from viruses in the cytoplasm or be taken up by endocytosis and transported to the cytosol. These proteins are then ubiquitinated and degraded into peptides by the proteasome. The resulting peptides in the cytosol are then transported into the ER lumen by TAP (Transporter Associated with Antigen Processing), where they are placed on MHC Class I molecules and then transferred to the cell surface.
What is the role of the invariant chain in the Class II antigen presentation pathway?
In the Class II antigen presentation pathway, the invariant chain plays a role in stabilizing the MHC Class II molecule and preventing it from binding other peptides prematurely. It is later removed by CLIP (Class II-associated invariant chain peptide).
What is the importance of RNA processing in the context of B-cell receptor expression?
RNA processing is an important step in the co-expression of IgD and IgM on B-cells, as well as in determining whether IgM is expressed in a membrane-bound or secreted form. The pre-mRNA looks the same, and alternative RNA processing decides if the mRNA will code for IgD or IgM, and membrane bound or secreted form
True or false: T-cell receptors can recognize native antigens without them being processed and displayed by MHC molecules
False
True or false: MHC Class I molecules are found on all cell types in the body, including blood cells
False; blood cells do not exhibit any MHC receptors.
True or false: MHC Class I molecules typically bind peptides that are between 13-18 amino acids in length.
False; they bind shorter peptides (8-10 aas)
In MHC Class I, the bound peptide is tightly bound along the entire length of the peptide-binding groove.
False; they are bound tightly at the ends. In Class II MHC, this is the case.
True or false: T-cell receptor binding to the MHC:peptide complex is sufficient for T-cell activation and does not require additional co-receptors.
False; additional co-receptors such as CD4/CD8 are necessary. Furthermore, binding of second signals like CD28 to B7 are also necessary.
True or false: CD8 co-receptors are primarily found on cytotoxic T-cells that interact with MHC Class I molecules.
True
True or false. The TAP transporter is responsible for moving peptides from the ER lumen into the cytoplasm for loading onto MHC Class I molecules
False; it is the other way around
True or false: The invariant chain in the Class II antigen presentation pathway helps to stabilize the MHC Class II molecule and prevents it from binding other peptides in the ER.
True
True or false: CD1 molecules present peptide-based antigens to conventional T-cells.
False; CD1 molecules are markers on delta-gamma T-cells, and can present lipid based antigens to unconvential T-cell subsets
True or false. Cytokines are exclusively produced after the differentiation of immune cells to exert their effector functions.
False
