Lecture 4: MHC & Ag Presentation to TCells Flashcards
Bare Lymphocyte Syndrome is a form of _____ caused by…
SCID
Mutations in MHC (either type 1 or type 2)
T cell recognizes antigen via ______ molecule on an APC
MHC
Major class 1 genes are…
HLA - A,B,C
Minor class 1 genes
HLA – E,F,G,H,J,X
Major Class II genes
*HLA-D*
DP – A1,A2, B1,B2
DQ – A1, A2, B1, B2, B3
DR – A, B1, B2, B3
Major Class III genes are _________ and have _______________
Diverse
Non-antigen presenting functions
Class ___ region of HLA are the farthest
Class I
BCE AGF
Class ____ region is the closest on the HLA complex
Class II
DP, DQ, DR
HLA genes that are not expressed (not funcitonal) are referred to as _______
pseudogenes
The MHC on every human chromosome 6 contains one gene for ____ and _____
DRA
DRB1
Any ____ chain can pair with the ____ chain to form a class II Molecule
DR-B
DR-a
MHC I structural domains
alpha 1 + 2 + 3
beta 2
MHC I – peptide binding site formed by _____ domains
a1 + a2
MHC I Molecule is anchored to cell membrane by ____ domain(s)
a3
B2 microglobulin is ________ but __________
invariant but essential
The alpha chain of MHC is also known as the _____ chain
heavy
MHC II is composed of one ___ chain and one ____ chain
one alpha and one beta chain
MHC II peptide binding site is composed of ______ domain(s)
a1 and b1
For MHC II, which chains are variable and which are constant?
a1 + b1 are polymorphic (variable)
a2 + b2 domains are constant
T cell structural domains:
V-alpha + V-beta
C-alpha + C-beta
T cell antigen binding region comprised of ___ and ____ domains
V a/b
The peptide binding groove of MHC molecules is made of about ____ peptides
8 - 15
Rank the top three MHC I HLA’s in terms of polymorphism.
What cells do these correspond to?
B > A > C
CD8 T-cells + NK cells
MHC class I effect on CD8+ cells and NK cells?
Activate CD8+ cells
Inhibit NK cells
Polymorphism definition…
presence of multiple alternative alleles of a gene
What is, by far, the most highly polymorphic MHC II allele?
DRB1
DMA/DMB
DOA/DOB
These genes serve what function in MHCII
Help peptide loading
O+M
DP, DQ, and DR genes provide what function for MHC II
Present antigen peptides to CD4+ Tcells
Polymorphism allows the human population to ___________
hadle a variety of pathogens
MHC genes exhibit _______.
_______ are expressed.
Co-Dominance
Both alleles are expressed
In any mating, ______ possible combinations of haplotypes can be found in the offspring (for MHC molecules)
4 combinations
(With regard to chromosome 6) A **haplotype **is a…
particular combination of MHC alleles found on a given chromosome 6
HLA -E and HLA-G are ____ and interact with ______
Oligomorphic
NK cell receptors
HLA-F function
Unknown. It remains intracellular with a SINGLE isotype.
Common function to HLA A, B, and C?
Present Antigen to CD8+ cells
Common function to HLA-DP, DQ, and DR?
Present antigen to CD4+ cells
____ is the most highly polymorphic allele for MHC-II
HLA-DRB1
MHC class II variablity is due to the ___ domain because the _____ chain is monomorphic
Beta 1 domain
The alpha domain is **monomorphic **(a1+a2)
Each MHC molecule binds a characteristic set of peptides. ________ in these peptides are important for binding to MHC
Anchor residues
What is “degenerate binding”
the property which allows each MHC molecule to handle many different peptides
MHC I molecules bind mostly _____ peptides, and positions __ and __ are the usual anchor residues.
Nonamer peptides
Positions 2 and 9
Some MHC II can have mor ethan 3 isotpes because there may be more than one _____. This means a cell will have what combination?
DR gene
DRB1 + DRA (like all cells) WITH either DRB3, DRB4, or *DRB5 *
(In both MHC I and II) which are the most polymorphic
HLA-B and HLA-DRB1
____ is most monomorphic HLA
HLA-DR-α
HLA _______ are present in only some people
HLA DRB3, DRB4, DRB5
Most people are ______ (genetically) and express ________
Heterozygotes
Two Haplotypes
A person can express _____ Class I isoforms and ______ Class II isoforms.
3-6
3-8
There are _____ MHC I isoforms and _____ MHC II isoforms in the human population
753 Class I
2406 Class II
MHC__ is expressed in all cells
MHC 1
These four cells are the only ones to express high levels of both MHC 1 and II molecules.
B cells
MQ
DC
Thymic epithelial cells
These are the three APC cells
B cells, MQ, DC
_______ do not express either MHC I or II
Erythrocytes
___ increased MHC II expression in APC’s. What is the other effect?
IFN - Gamma
it induces the expression of MHC II in non-APC’s at the sites of infection
MHC II handles ____ antigens
Extracellular
Antigen processing for MHC II (process)
- Extracellular ag endocytosed
- -> phagolysosome
- MHC II in vesicle goes and binds Ag
- MHC II presents the Ag at the surface
MHC Class I handles ____ antigens
Intracellular
MHC class I Antigen processing (steps)
Ag in cytoplasm is ubiquinated
-> Proteosome
Transport to ER
Bind MHC *in ER*
Presented at surface
Intracellular Ag’s are handled by _____ and they can originate from ___ (such as ___)
MHC I
viruses (such as HIV)
MHC I proteins are assembled in ER and associate with ___ and ___
TAP protein
Calnexin (Chaperone)
TCR’s do not bind to ___ but rather to ____
Dont bind whole antigens
instead bind to antigen peptides
Transport of peptides to ER requires
TAP
Transporter associated with Antigen Processing
What happens when you don’t have TAP protein
Bare Lymphocyte syndrome
_No TAP _ = No MHC1 = _No CD8+ _ = No Cytotoxicity
= Chronic Respiratory infection
TAP is made of
TAP1 + TAP2
_____ length polypeptides are transported via TAP
8 or more amino acids
MHC1 cant ______ without peptides being loaded
can’t leave ER
Three molecular chaperones that aid in MHC folding and loading of peptides:
Calnexin
Calreticulin
Tapasin
MHC class 1 is stabilized by ____ in ER until ____ binds
Calnexin
B2
In absence of infection, _____ are presented on MHC but these ________
self peptides
do not activate T cells
After synthesis in the ER, MHC 2 peptide binding site is protected by
CLIP region of **Ii **
(Invariant chaperone)
CLIP is removed from MHC II by _____
HLA DM protein
____, ___, and ____ guide the peptide loading of MHC II
invariant chain
CLIP
HLA-DM
What must happen after CLIP is gone?
MHC II needs to bind to peptide or it will be degraded
Where do MHC II bind to peptides?
In fused vesicles
CD8 ___ group binds to the ____ group on the MHC molecule
CD8 alpha group binds to a3 on MHC1
CD4 binds to ____ group on MHCII
B2 group
T cell receptor recognitionof antigens is _________
MHC restricted
A TCR may not recognize a particular peptide when it is bound to a different class of MHC, or a different peptide on the *same *MHC
CD8 kills virus infected cells how?
directly
CD4 T cell does what to stimulate other cells?
Makes cytokines
Activate macrophage to make its own cytokines
Activate B cells (to plasma cell) to make Antibodies
HLA typing is dome via what methods
Microcytotoxicity Assay
RFLP
PCR
Flow Cytometry/ELISA
Microtoxicity Assay uses ____ which is mixed with lymphocytes
Exogenous complement is added which results in ….
Anti-HLA serum
results in lysis of cells that have bound Antibody
During RFLP, DNa is digested and hybridized to
Radiolabeled MHC
PCR uses
MHC specific primers
ELISA uses
monoclonal antibodies to MHC alleles
Other test for HLA compatibility
What are we looking for?
Mixed Lymphocyte Reaction test
Higher response = higher the match
Disease for DR3 + DR2
SLE
Disease for DR4
Rheumatoid Arthritis
DIsease for B7 and DR2
MS
Disease for B8 + DR3 + DR4
T1DM
Disease for B27
Ankylosing Spondylitis
