Major Histocompatibility Complex/ Antigen Presentation Flashcards
What cells only recognize antigens presented on the surface of other cells?
T-cells
How are antigens presented on the surface of cells?
MHC molecule
Do BCRs/ antibodies need antigen presented on MHC to be recognized?
no- can interact with free-floating antigen
- unlike T-cells, need bound
How are T-cells presented with antigens?
MHC
What binds to the MHC molecule inside cell?
antigen
How is antigen presented on MHC cell surface?
digestion/ complex transported
What are professional APC’s?
Dendritic cells
Macrophages
What act as “cell surface vessels”?
MHC molecules
Where is antigen binding to MHC molecules generated?
inside cell
What hold/ display fragments of antigen so T-cells can interact with their TCRs?
MHC (cell surface vessel)
How are MHC genes spread within the population?
alleles inherited
-contribute to individual response to infection/ disease susceptibility/ autoimmunity development
How do MHC molecules attach to cell membrane?
transmembrane segment- stability
What are the 2 classes of MHC molecules?
MHC I
MHC II
Where on the MHC does the antigen bind?
Peptide-binding groove
How many transmembrane domains does MHC class I molecule have?
1
How many transmembrane domains does MHC class II domain have?
2
What MHC molecule has 3 alpha domains and
1 B-microglobulin domain?
MHC I
What MHC molecule has a narrow/ shallow peptide binding groove?
MHC I
What MHC molecule is involved in self-peptide recognition?
MHC I
What MHC molecule is constitutively expressed?
(always expressed- screening)
MHC I
What MHC molecule is associated with 2 globulin structures (1 alpha/ 1 beta side) ?
MHC II
B1+B2 / a1+a2
What MHC molecule has a deep peptide binding groove (goes all way through)?
MHC II
What term describes peptide/ antigen binding?
variable
How many different peptides can an MHC molecule bind?
numerous
What makes up the MHC I peptide-binding domain?
a1/a2
What makes up the MHC II peptide-binding domain?
a1/B1
What MHC molecule is closed at both ends (shorter)?
MHC I
What MHC molecule is open at both ends?
MHC II
What MHC molecule do larger peptides bind to?
MHC II
What T cell does MHC class I present peptides to?
CD8+
Why does MHC I bind peptides from intracellular sources?
recognizes self-antigens/ peptides
How long are the peptides bound to MHC I?
8-10 AA
What are the specific amino acids at key locations in MHC I bound peptide?
Anchor residues
What T cell does MHC class II present peptides to?
CD4+
What peptides does MHC II bind?
extracellular/ variety
How long are the peptides bound to MHC II?
13-18 AA
Peptides bound to which MHC class are less conserved?- greater variability (sequence/ length)
MHC II
What are other names for MHC?
HLA = human leukocyte antigen
H2 =mice
What AA are the same/ specific between all MHC class I proteins?
anchor point = anchor residues
What is a common problem for antigens/ receptors?
bind wide variety antigens with strong affinity
What 2 combinations allow MHC molecules to bind an antigen?
Peptide-binding promiscuity
expression of different MHC variants on each cell
Why are MHC variants/ peptide-binding promiscuity important?
maximize recognition of different epitopes of antigen
What are parts of antigen that are recognized?
Epitopes
What are the 3 classes MHC genes are organized into?
I/ II/ III
What are the 2 kinds of MHC genes?
Classical
Non-classical
What MHC classes are classical?
I/ II
What MHC classes are non-classical?
III
Why are MHC class III genes non-classical?
no direct role in presenting antigens to T cells
- indirect immune functions
What MHC molecule is associated with cytotoxic T cells?
MHC I = CD8 = cytotoxic T
What MHC molecule is associated with helper T cells?
MHC II = CD4 = T helper
Where are the glycoproteins of MHC I expressed?
surface of nucleated cells
(neutrophils/ platelets)
Where are the glycoproteins of MHC II expressed?
surface of APCs
= dendritic cells/ macrophages
What MHC molecule is primarily present on exogenous/ extracellular peptides/ antigens?
MHC II
What MHC classes are glycoproteins?
I/ II = glycoproteins
III = diverse set proteins
What are immune functions of MHC class III?
encode complement proteins- C4/C2/ factor B
inflammatory cytokines - TNF
What are 2 consequences of disruption to MHC III?
susceptibility to infectious diseases
autoimmune diseases (chrohns/ MS)
- constant/overproduction inflammatory cytokines
What is the term when many alternate forms of each gene are in a population?
Polymorphic
What is the term for alternate forms of genes?
Alleles
What is the inherited set of linked alleles termed?
Haplotype
How is a set of MHC genes inherited?
set alleles inherited as 1 unit, from each parent
= Haplotype
Why is there not a lot of MHC gene recombination?
tightly linked
What 2 terms describes MHC genes?
highly polymorphic
tightly linked
How are MHC molecules expressed?
Co-dominantly
What is it when both maternal/ paternal haplotypes are expressed at same time?
Co-dominance
What allows a cell to present a large # of different peptides?
expression of different MHC I molecules
- each different binding affinities
How many MHC I molecules are there?
6
How many MHC II molecules are there?
12
What is the term for containing multiple genes with the same function but slightly different structures?
Polygenic
How are host cells displayed as healthy?
self MHC I/ self-peptide display
How can a foreign protein show host cell is infected? MHC I
MHC I peptide display- activate T-cytotoxic cells
How can a foreign protein show host cell is infected? MHC II
MHC II peptide display- activate T-helper cells
How are T cells tested?
MHC I/ II display self-peptides
- test for autoreactivity
Where are t-cells tested for autoreactivity?
(positive/ negative selection)
primary lymphoid organ = thymus
How is tolerance to self-proteins done in secondary lymphoid tissues?
display self peptide MHC I/ II
What MHC molecule is constitutively expressed?
MHC I
How/ where is MHC II expressed?
variable/ on limited cells (APC)
What is MHC II expression controlled by?
genetic regulatory components
viral interference
cytokine-mediated signalling
What effect does cytokine binding to receptors have on MHC II expression on APCs?
increases
What effect do genetic regulatory components have on MHC expression?
induce signal transduction cascades
What effect does viral interference have on antigen presentation via MHC I?
inhibit
When can CD4+/ CD8+ recognize an antigen?
only when presented in groove of MHC
What must match for recognition? (APC/ T cell)
MHC haplotype
What happens if you fix/ block MHC molecule on APC?
antigen can not bind/ no t cell recognition
What MHC is associated with endogenous antigens?
MHC I
How are endogenous antigens processed?
cytosolic/ endogenous pathway
How are exogenous antigens processed?
exogenous pathway
How are exogenous antigens presented on APC membrane?
MHC II
Where are endogenous antigens generated?
within cell
Where are exogenous cells generated/ taken up?
taken up from extracellular environment
- via endocytosis
What is an example of MHC II antigen?
bacteria/ fungus
How are intracellular proteins degraded into peptides?
by proteosome
How are proteins tagged for degradation? (protein-peptide)
ibiquitin
What can activated infected cells temporarily express?
immunoproteosome
What proteins in the cytosolic protein pool are degraded by proteosomes?
those tagged by ibiquitin
What are the 3 steps in the endogenous pathway?
- proteolytic cleavage by proteasome
- peptide transport to cytosol to RER
- chaperones aid peptide- assembly with MHC
What does MHC I present on?
nucleated cells- includes APCs
What are the steps in exogenous pathway?
- receptor-mediated endocytosis
- degradation to peptides
- interaction between MHC II/ peptide
- antigen presentation
- interaction peptide/ MHC II
What is the term when an antigen acquired by exogenous pathway is redirected to endogenous pathway so peptides presented on MHC I?
cross-presentation
What are some non-peptide antigens?
small lipid containing antigens
small molecules/metabolites
What is different in MHC I for non-peptide antigens?
peptide-binding groove
CD1 protein class ex- MR1