MDSC 321 Final Exam With
Complete Solution
What is MHC? - Answer Major histocompatibility complex
What was MHC first recognized for? - Answer Self/non-self discrimination in transplant
rejection
What is MHC absolutely essential for? - Answer Displaying an antigen to T-cells
What is the only way T-cells can see antigens? - Answer In the context of self MHC
How many classes of MHC are there? Define them and their function. - Answer I -
presentations of antigens inside the cell to killer T-cells
II - presentation of extracellular antigens to helper T-cells
III - secreted proteins not involved in antigen presentation
Where is MHC II expressed? - Answer Only in membranes of antigen presenting cells
(macrophages and dendritic cells and B-cells)
What are the names of the 3 genes MHC II has? - Answer HLA-DP, HLA-DQ, HLA-DR
How many chains does each MHC II gene have? - Answer 2 chains - alpha and beta
Where is MHC I NOT expressed? - Answer Red blood cells
How many chains do MHC I genes have? - Answer 1 chain - alpha
What are the names of the genes MHC I has? - Answer HLA-A, HLA-B, HLA-C
What does polygenic mean? How many genes does MHC have? - Answer more than 1
gene; MHC has 6
True or False: not all MHC molecules within an individual are the same. - Answer False.
MHC molecules differ between individuals, but are the same within one.
What is MHC a result of? - Answer Polymorphism
What is a polymorphism? How do they arise? - Answer multiples alleles in a gene loci;
arise due to mutations
How many MHC are expressed on an antigen presenting cell? Explain where they come
from. - Answer (3 MHC I + 3 MHC II from mom) + (3 MHC I + 3 MHC II from dad) = 12
Where does the diversity in an MHC molecule occur? - Answer Peptide binding cleft
,What is/are the difference(s) between the peptide binding cleft of MHC I and II? What do
these differences mean? - Answer Class I has cleft that is closed at the end - peptide
must be completely contained
Class II has cleft that is open at the end - peptide is exposed flat across the surface like
a hot dog in a bun
What is antigen processing? - Answer Degradation of the antigen into peptides
What is antigen presentation? - Answer Binding of peptide to MHC and displaying it to
interact with T-cells
What is TAP? - Answer Transporter of antigenic peptides
Explain the 5 steps of antigen processing for MHC I. - Answer 1. Identify antigens
2. Cleavage of the protein done by proteasome
3. Transport to ER done by TAP
4. Peptides loaded into binding cleft
5. Whole complex transported to surface within vesicles
What stabilizes MHC while it waits for a peptide to be loaded? - Answer Chaperone
proteins
Explain the 6 steps of antigen processing for MHC II. - Answer 1. Internalization of target
into phagosome/endosome
2. Digest the antigen in the endocytic pathway
3. Make MHC II in the ER
4. Vesicles with MHC II are moved to the Golgi and fuse with endolysosomes
5. Peptide loaded into binding cleft
6. Transport whole complex to surface within vesicles
How many chains does a TCR have? - Answer 2
What are the chains of a TCR held together by? - Answer Disulfide linkage
What is TCR antigen recognition mediated by? - Answer V domain of both peptide chains
How many hypervariable loops contact the antigen in a TCR? Name them. - Answer 1 -
CDR3
Is there anything else that contributes to antigen recognition? - Answer An extended
looping structure called HV4
, True or False: TCR contacts both MHC and the antigen simultaneously. - Answer True
Which hypervariable domain does most of the antigen recognition? - Answer CDR3
What do the remaining hypervariable domains recognize? Name them. - Answer CDR1
and CDR2 recognize the MHC
What is self-restriction? - Answer TCR repertoire is generated through the
positive/negative selection of immature T-cells in the thymus - if it doesn't recognize
MHC, it is killed
What are the 2 co-receptors that engage the MHC-antigen complex? What do they bind
to? - Answer CD8 (killer) - binds to MHC I
CD4 (helper) - binds to MHC II
What does the binding of co-receptors to MHC result in? - Answer Lowers activation
threshold of T-cells - T-cells can recognize much smaller infections
What is CD3? - Answer Signalling molecule
True or False: the cytoplasmic tail of the TCR can mediate intracellular signalling on its
own. - Answer False. Does all signalling with ITAM motifs
Explain the twist on the 12/23 rule that occurs with TCR. - Answer With B-cells, it is
impossible to have 2 D's join together.
T-cells have alternative joining of D segments (can have VJ, VDJ, VDDJ)
How is additional variation created within the T-cell repertoire? - Answer Junctional
diversity - P and N nucleotides added between each TCD segments
Which hypervariable loops do NOT have diversity? Why? - Answer CDR1 and CDR2 -
must recognize MHC every time
Does allelic exclusion occur in TCR? Is it as strict? - Answer Yes and no
Why is allelic exclusion with TCR not as strict? - Answer T cells without allelic exclusion
will still always produce cytokines and kill the target as long as it sees the target
B cells without allelic exclusion will produce antibodies that bind the antigen AND
potentially self molecules (autoimmunity)
What is immunodiffusion? - Answer The ability of an antigen and an antibody to
precipitate together.
What is the area of precipitate proportional to in an immunodiffusion? - Answer Area of
precipitate is proportional to antigen concentration
Explain the process of immunoelectrophoresis. What is this process similar to? - Answer
1. Antigen mix is separated via electrophoresis
Complete Solution
What is MHC? - Answer Major histocompatibility complex
What was MHC first recognized for? - Answer Self/non-self discrimination in transplant
rejection
What is MHC absolutely essential for? - Answer Displaying an antigen to T-cells
What is the only way T-cells can see antigens? - Answer In the context of self MHC
How many classes of MHC are there? Define them and their function. - Answer I -
presentations of antigens inside the cell to killer T-cells
II - presentation of extracellular antigens to helper T-cells
III - secreted proteins not involved in antigen presentation
Where is MHC II expressed? - Answer Only in membranes of antigen presenting cells
(macrophages and dendritic cells and B-cells)
What are the names of the 3 genes MHC II has? - Answer HLA-DP, HLA-DQ, HLA-DR
How many chains does each MHC II gene have? - Answer 2 chains - alpha and beta
Where is MHC I NOT expressed? - Answer Red blood cells
How many chains do MHC I genes have? - Answer 1 chain - alpha
What are the names of the genes MHC I has? - Answer HLA-A, HLA-B, HLA-C
What does polygenic mean? How many genes does MHC have? - Answer more than 1
gene; MHC has 6
True or False: not all MHC molecules within an individual are the same. - Answer False.
MHC molecules differ between individuals, but are the same within one.
What is MHC a result of? - Answer Polymorphism
What is a polymorphism? How do they arise? - Answer multiples alleles in a gene loci;
arise due to mutations
How many MHC are expressed on an antigen presenting cell? Explain where they come
from. - Answer (3 MHC I + 3 MHC II from mom) + (3 MHC I + 3 MHC II from dad) = 12
Where does the diversity in an MHC molecule occur? - Answer Peptide binding cleft
,What is/are the difference(s) between the peptide binding cleft of MHC I and II? What do
these differences mean? - Answer Class I has cleft that is closed at the end - peptide
must be completely contained
Class II has cleft that is open at the end - peptide is exposed flat across the surface like
a hot dog in a bun
What is antigen processing? - Answer Degradation of the antigen into peptides
What is antigen presentation? - Answer Binding of peptide to MHC and displaying it to
interact with T-cells
What is TAP? - Answer Transporter of antigenic peptides
Explain the 5 steps of antigen processing for MHC I. - Answer 1. Identify antigens
2. Cleavage of the protein done by proteasome
3. Transport to ER done by TAP
4. Peptides loaded into binding cleft
5. Whole complex transported to surface within vesicles
What stabilizes MHC while it waits for a peptide to be loaded? - Answer Chaperone
proteins
Explain the 6 steps of antigen processing for MHC II. - Answer 1. Internalization of target
into phagosome/endosome
2. Digest the antigen in the endocytic pathway
3. Make MHC II in the ER
4. Vesicles with MHC II are moved to the Golgi and fuse with endolysosomes
5. Peptide loaded into binding cleft
6. Transport whole complex to surface within vesicles
How many chains does a TCR have? - Answer 2
What are the chains of a TCR held together by? - Answer Disulfide linkage
What is TCR antigen recognition mediated by? - Answer V domain of both peptide chains
How many hypervariable loops contact the antigen in a TCR? Name them. - Answer 1 -
CDR3
Is there anything else that contributes to antigen recognition? - Answer An extended
looping structure called HV4
, True or False: TCR contacts both MHC and the antigen simultaneously. - Answer True
Which hypervariable domain does most of the antigen recognition? - Answer CDR3
What do the remaining hypervariable domains recognize? Name them. - Answer CDR1
and CDR2 recognize the MHC
What is self-restriction? - Answer TCR repertoire is generated through the
positive/negative selection of immature T-cells in the thymus - if it doesn't recognize
MHC, it is killed
What are the 2 co-receptors that engage the MHC-antigen complex? What do they bind
to? - Answer CD8 (killer) - binds to MHC I
CD4 (helper) - binds to MHC II
What does the binding of co-receptors to MHC result in? - Answer Lowers activation
threshold of T-cells - T-cells can recognize much smaller infections
What is CD3? - Answer Signalling molecule
True or False: the cytoplasmic tail of the TCR can mediate intracellular signalling on its
own. - Answer False. Does all signalling with ITAM motifs
Explain the twist on the 12/23 rule that occurs with TCR. - Answer With B-cells, it is
impossible to have 2 D's join together.
T-cells have alternative joining of D segments (can have VJ, VDJ, VDDJ)
How is additional variation created within the T-cell repertoire? - Answer Junctional
diversity - P and N nucleotides added between each TCD segments
Which hypervariable loops do NOT have diversity? Why? - Answer CDR1 and CDR2 -
must recognize MHC every time
Does allelic exclusion occur in TCR? Is it as strict? - Answer Yes and no
Why is allelic exclusion with TCR not as strict? - Answer T cells without allelic exclusion
will still always produce cytokines and kill the target as long as it sees the target
B cells without allelic exclusion will produce antibodies that bind the antigen AND
potentially self molecules (autoimmunity)
What is immunodiffusion? - Answer The ability of an antigen and an antibody to
precipitate together.
What is the area of precipitate proportional to in an immunodiffusion? - Answer Area of
precipitate is proportional to antigen concentration
Explain the process of immunoelectrophoresis. What is this process similar to? - Answer
1. Antigen mix is separated via electrophoresis
