Immunology

List the major steps involved in T cell receptor (a/b) formation. Start with the germline DNA and include any molecules that arrive and play a role in T cell development.

1. Progenitor T cell has no recombination until it reaches the thymus 2. D-J gene segment rearrangement of the beta gene for the T cell receptor (TCR) 3. V-DJ gene segment rearrangement of the beta gene 4. Transcription and translation of Beta gene to form a variable and constant region; recombination stops 5. CD3, CD4, CD8, pTA and beta chain expressed on cell surface. Pre TCR formed between beta chain and pTa. 6. V-J gene segment of alpha gene for the TCR is reaaranged 7. CD3, CD4, CD8, beta chain, and alpha chain expressed on T cell surface

3) What are the 4 outcomes of the formation of the LAT-SLP-76-GAD complex?

3) -PI3-K activation of AKT-- this increases metabolic activity-PLC-y-- transcription activatio-ADAP (adaptor)-- increases integrin adhesion and clustering/ helps T cell ability to mobiliz-Vav actin polymerization and cytoskeleton reorganization for cell movement

How many chains make up the TCR? Which one is inside of the cell?

4; zeta chains inside cell

5)What are two inhibitors of the JAK/STAT pathway and ways in which they inhibit?

5) SOCS- competes and inhibits JAK can do this by... -Competes for docking site on receptor by binding at Phosphorylated tyrosine and blocking STAT recruitment (CIS)-Binds directly to JAK and inhibits kinase activity (SOCS1)-Bind directly to receptor and inhibit JAK (SOCS3)-Facilitates ubiquintination of JAKs PIAS- inhibits STAT only can do this by ... -binding to DNA (PIAS 1 and 3)-recruitment of histone deactylases (PIASX, PIASY) PTPs-- dephosphorylate

The CCL21 on a lymphocyte is not working correctly. Can the T cell still enter the lymph node with this deficiency? a. No, without CCL21, CCR7 won't be signaled to bind to it and LFA-1 will not be activated to bind to ICAM-1. b. No, without CCL21, L-selectin cannot bind to GlyCAM1 on the high endothelial venules, and rolling can't be initiated. c. Yes, the T cell will still have all of the receptors, selectins, and integrins on it, so it can still enter the lymph node. d. Yes, as long as ICAM1 is on the membrane, LFA1 is not needed to allow the T cell to enter.

A

When can STATs enter into the nucleus? a) once they dimerize and are phosphorylated b) once they are phosphorylated c) they can freely enter at any time d) They never enter the nucleus

A

Which molecule is responsible for the expression of tissue-specific proteins in the thymus?

AIRE

What 4 things is signal strength dependent on?

Affinity of receptor on T cell for ligands on APC Abundance of ligand on APC Concentrations of IC signaling components Complex network of + and - feedback pathways

Compare and contrast the B cell activation signaling with T cell activation signaling (3 examples total)

Answer examples: a. Src kinases involved in phosphorylation of ITAM motifs differ between the two- T cells use Lck and Fyn while B cells use Blk, Fyn, and Lyn. b. PI3K is recruited and activated in both to phosphorylate PIP2 into PIP3 c. PIP3 recruits Akt to cell membrane for activation and eventual upregulation of mTOR in both

There is a mutation that causes cells do undergo apoptosis more frequently. Which of the following would be the most likely protein to have a mutation? a. ICAD b. B7 c. AIRE d. CXCR5

Answer: A

1. Which of the following are required for proper development of a CD4-positive T cell? (Multiple answers could be correct) a. CD28 costimulatory signal b. Ubiquitous reaction with self-antigen on cortical epithelial cell c. Stromal cells expressing MHC Class I d. Germline encoded specificity for TCR Vbeta and Valpha e. AIRE

Answer: A,D

The majority of T cells die after one week in the thymus. Explain how this is beneficial to the body, even though it appears to be a waste of energy.

Answer: Although the majority of T cells die early on during T cell selection, it is more important to your body to have extremely selective T cells than it is to have a large number of T cells. The cells that die were likely overly self-reactive to the body's own MHC.

1. What is/are the fate-specifying cytokine(s) responsible for leading to TFH cells? a. IL-4 b. IL-6 c. TGF-B & IL-2 d. None of the above

Answer: B

1. Which of the following is/are mechanism(s) by which signaling proteins are recruited to the membrane? a. Protein binding to ITAMS b. Tyrosine phosphorylation of the BCR or TCR c. Local production of modified membrane carbohydrates d. Phosphatases acting upon an associated scaffold e. All of the above

Answer: B

If there is a mutation in the Ikaros gene that made it nonfunctional, what would you expect to happen? a. Dendritic cell development would not occur b. Lymphocyte development would not take place c. B cell development would not occur d. Heavy chain rearrangement would take longer

Answer: B

While working in a lab, you notice that transcription via the MAPK pathway is being impaired. You also realize that there is a significant decrease in effector molecules produced by the immune cells. What could be the cause this to occur? a. Mutations in the MHC b. Mutations that impair the TCR c. An increase in lipopolysaccharide d. Ubiquitination of Erk

Answer: B

1. If a patient with SCID undergoes gene therapy and regains production of functional NK cells, but not their humoral immunity, which infections will the patient have more difficulty clearing/recovering from: viral or bacterial?

Answer: Bacterial infections will be more difficult to clear. NK cells are responsible for viral infection response

What is the importance of Csk and CD45 in regards to Lck?

Answer: Both Csk and CD45 regulate Lck. Csk apart of the Src family of kinases phosphorylates Lck to make it inactive by binding the SH2 domain and the linker region binding to SH3 domain. Cd45, a phosphatase, removes the phosphate on Lck to activate it so that the SH3 domain releases the linker region and allowing it to bind to CD3 to phosphorylate and activate other proteins.

Which of the following is NOT an outcome from the LAT-SLP76-gad complex pathways? a. LFA-1 integrin increases b. Cytoskeleton changes c. Pro-apoptotic signaling increases d. metabolic activity increases

Answer: C

Which of the following is not true regarding macrophage activation? a. They are activated by TH1 cells b. They require two signals to be activated c. TNFa is required to activate macrophages d. IFNg is required to activate macrophages

Answer: C

1. If a person is born with a genetic mutation making their AIRE gene non-functional, which of the following would be the most likely to occur in the body? a. More T cells become anergenic than usual b. Buildup of immature T cells in the thymic cortex c. Higher likelihood of developing autoimmune disease d. Problems in activating their T cells to perform effector functions

Answer: C. Self-reactive lymphocytes are not completely removed from the pool of naïve T cells à increased chance of autoimmune disease

1. What protein does LFA-1 bind to? a. ICAM-1 b. ICAM-2 c. CD58 d. A & B e. A & C

Answer: D

Which of the following is NOT a non-receptor tyrosine kinase? a. integrins b. selectins c. LFA-1 d. GPCR

Answer: GPCR

An individual has a mutation in the gene that codes for the MAP kinase MEK1. How will this affect the individual's immune cells?

Answer: In a normally functioning T or B cell, signaling allows for DAG to be produced from the break down of PIP2 by the enzyme PLC-y. DAG usually then recruits RasGRP and PKC-theta. RasGRP is a GEF for Ras so Ras is usually then activated. When Ras is activated, the MAPK pathway can be activated. If MEK1 is not functioning, Raf can be activated but the pathway cannot continue on any further than that. Ultimately, this means that the FOS gene cannot be transcribed to create the Jun/Fos dimer (aka AP-1). AP-1 is a transcription factor that is needed in order for IL-2 genes to be transcribed. The individual's immune cells will not be able to produce IL-2 and will not be able to proliferate.

Compare and contrast T cell and B cell signaling.

Answer: In both T cell and B cell signaling there are tyrosine kinases, adaptors and scaffold proteins, phospholipases and lipid kinases, GTPases, serine/threonine kinases and phosphatases are all used which results in transcription factors, cytoskeletal changes, adhesion, and metabolic changes. However, in T cell signaling Lck phosphorylates the ITAMs which allows Zap-70 to be recruited and also phosphorylated. From there, Zap-70 phosphorylates LAT and SLP-76 to form the LAT:Gads:SLP-76 complex. This complex can recruit PLC-y and PI3K to allow downstream effects to occur. In B cells, Fyn, Lyn, or Blk are able to phosphorylate the ITAMs and CD19. The phosphorylated ITAMs attract Syk which can be activated by Fyn, Lyn, or Blk. Syk then goes on to activate SLP-65 while phosphorylated CD19 recruits PI3K. Both of these molecules can cause downstream effects within the B cell.

How does HIV/AIDS highlight the importance of macrophage activation done by CD4 T cells?

Answer: In individuals with HIV/AIDS, they have an extremely low count of TH1 CD4 T cells. Consequently, when the affected individuals comes in contact with a bacterial pathogen their body is not able to effectively combat it. This is due to the fact that TH1 cells help to establish an immune response against extracellular bacteria and activate macrophages so they can undergo phagocytosis. Without this cell population, individuals with HIV/AIDS are extremely susceptible to uncontrolled infections which can sometimes lead to death.

1. Which two molecules in the LAT:Gads:SLP-76 complex are phosphorylated by Zap70 in T cell activation?

Answer: LAT and SLP-76

Briefly explain how PIP3 is created in the B cell?

Answer: Once phosphorylation of ITAMs occurs on the IgB/Ig-alpha and CD19 tails of the co-receptor complex, PI3K is recruited to CD19 because it has an SH2 domain. PI3K then works to generate PIP3 on the membrane.

Why does the presence or absence of MHC2 in the thymus determine if there are mature CD4 T-cells?

Answer: T-cell maturation is mediated by signals from the epithelial and stromal cells of the thymus. CD4 T-cells recognize antigens bound to MHC2 molecules, and need to be tested for their reaction to self antigens. Without MHC2 molecules in the thymus they can recognize antigens on, they will not mature and will not exit the thymus.

Why do THF cells have a CXCR5 receptor?

Answer: THF cells activate B-cells, and that happens in the follicle region of the lymphocyte. Cells are guided to the follicle region by CXCL13 chemokine, which is received by the CXCR5 receptor. Without that receptor, THF cells wouldn't be able to enter the follicle region to activate B cells.

True/False. The development of CD4 T-cell subsets can be manipulated by altering the cytokines acting during early stage of infection

Answer: TRUE

1. True or false: When T-cells encounter their cognate antigen in a lymph node, CD69 expression is upregulated and S1PR1 expression is downregulated

Answer: True

What is the role of TH1 cells?

Answer: they release IFNy and activate macrophages.

What cells can you find Zap70? a. B cells and Macrophages b. T cells and NK cells c. Neutrophils and NK cells d. Macrophages and T cells

B

1. Why is the process for B-cells to have the correct receptor so selective?

Because the B-cells produce antibodies and if the antibodies bind to the wrong antigens then the body will start an immune response against the wrong thing.

What activates the protein kinase? What happens after?

Binding of ligand to extracellular part of receptor Then, it can phosphorylate IC substrate to propagate signal

Receptor editing takes place in

Bone marrow

List two similarities and two differences in B cell and T cell development.

Both T cell and B cell precursors will develop in the bone marrow. Both undergo negative selection to get rid of any cells that bind to self-antigens. Unlike B cells, T cells will migrate to the thymus to complete their development. T cells also undergo Notch signaling to initiate T cell gene expression.

Which of the following is an INCORRECT option for turning off signaling? A. Dephosphorylation of phosphorylated substrates B. Ubiquitin-mediated degradation by proteasome with polyubiquitin chains C. Ubiquitin-mediated degradation by proteasome with individual ubiquitin molecules D. Ubiquitin-mediated degradation by lysosome with individual ubiquitin molecules

C. Degradation by the proteasome has to have polyubiquitin chains in order to be targeted for destruction.

What would happen to a mouse with a genetic disorder that decreases the expression of CTLA-4 and why?

CTLA-4 is an inhibitory molecule on T-cells, which is induced after T-cell activation to bind with B7 dimers with a stronger affinity and avidity than CD28 to cease signaling and regulate T-cell activation. With a deficiency in CTLA-4 expression, the T-cells would remain activated without regulation, risking the mice to have an autoimmune disease.

Which cytokine binds with CXCR5?

CXCL 13

Which is unique to B-cell chemokine receptor?

CXCR5

Which event leads to the dephosphorylation of NFAT and what is the result of the dephosphorylation?

Calcium channels opened by IP3 and NFAT can enter the nucleus.

2) What is not a part of the SOCS structure a) SH2 domain b) KI c) SOCS box d) SH3 domain

D

All of the following are true of double negative T cells except for Double negative t cells will not express CD4 Double negative t cell will express CD8 Developing t cells start as double negative cells before specializing Double negative means the cells have nothing on their cell membrane

Double negative t cell will express CD8

Which pathway does the immunosuppressive FTY720 affect and how?

FTY720 immunosuppressive impacts the exit pathway of inactivated naïve T-cells from the lymph node to the blood circulation. The regular pathway is when the high concentration of S1P in the bloodstream chemically attracts inactivated T-cells with S1P receptors in the lymph node where there is a lower concentration of S1P than the blood. After interaction with S1P, naïve T-cells diapedesis from the lymph node to the bloodstream. The immunosuppressive prevents the T-cells from leaving the lymph node by downregulation the expression of S1PR1, where FTY720 causes internalization. *The inhibition of the T cells to exit the lymph nodes presents them from damaging or illiciting an immune response when it is not required

JAK-STAT is a signaling pathway that is important for gene transcription relative to cell death

False

T/F. JAK-STAT is a signaling pathway that is important for gene transcription relative to cell death

False

T/F: Naïve T cells circulate the body to detect antigens at the site of infection.

False

T/F: Th2 cells tend to promote allergic responses and protect against parasites by altering barrier immunity of epithelial cells.

False

True/false All Ub tagged proteins end up degraded.

False

1. True/False: CD8, CD45, and CD4 are co-receptors associated with the TCR. a. False, CD45 is phosphatase that acts upon LCK at the TCR. It is not a co-receptor.

False, CD45 is phosphatase that acts upon Lck at the TCR. It is not a coreceptor.

True/False If someone was experiencing a massive infection, they would be able to turn on their anergic B cells in order to help respond to the infection

False, anergic B cells will eventually die. Immunological ignorant cells could be woken up from a massive infection to help.

Describe the cascade of events that occur resulting in increased metabolic activity of the cell.

Formation of the LAT:Gads:SLP-76 formation after T cell activation leads to increased metabolic activity of the cell. PDK1 is recruited to the membrane and phosphorylates Akt. Akt is now activated and phosphorylates TSC1/2 allowing it to release Rheb. Rheb then is active and activates mTOR, and this signals for the cell to increase its lipid production, protein translation, ribosome biosynthesis, and mRNA synthesis.

Which two molecules in the LAT:Gads:SLP-76 complex areNOT phosphorylated by Zap70 in T cell activation?

Gad

Activation of macrophage requires 2 signals from T cells to stimulate killing of engulfed microorganisms. The primary signal is __________ .

IFN-y

NFAT, AP-1, and NFKb are transcription factors for which gene/protein?

IL-2

In combination with antigen recognition and signaling through the TCR, CD28 costimulation causes full activation of T cells by inducing the expression of ....

IL-28

Which of the following cytokines is secreted by both CD8 T cells and TH1 cells?

INF-y

Which of the following are important for B cell development?

Ikaros and PU1

During T cell extravasation, firm adhesion to the HEV is mediated by __________ that change their conformation to a high affinity state after TCR recognizes antigen:MHC.

Integrins

Explain the role of Lck in cell signaling.

Lck is an Src-family kinase that is responsible for phosphorylating the ITAMs in the cytosol of the T cell or B cell, in order to bind proteins that have SH2 domains, Zap70 and Syk. Lck is the start to the signaling cascade, which allows for the cell to differentiate and gain effector function.

Compare and contrast how Lck and Fyn mediate signals. How would the lack of one affect the immune response as compared to the other?

Lck is permanently associated with the part of CD4 or CD8 that is inside of the cell. It is a src-family kinase that is responsible for the phosphorylation of ITAMs. Both Lck and Fyn are part of the first signal in the signaling cascade to activate T cells. Fyn is a tyrosine kinase that is weakly associated with the ITAMs on the part of the TCR that is inside the cell. It has a small role in this first signaling process. The lack of Fyn does not affect the development of normal CD4 and CD8 cells, while the lack of Lck does. However, the lack of both Lck and Fyn is more detrimental to T cell development than that lack of just Lck, so Fyn must play some role in signaling.

______ phosphorylates the ITAMs on the TCR. Then, the ITAMs recruit______. This molecule phosphorylates______ and _____ leading to the formation of the LAT:Gads:SLP-76 complex.

Lck, Zap-70, LAT and SLP-76

Describe, generally, what MAPK signaling is and why it is important (You can list in steps or give a general description).

MAPK activation in begins with a binding which leads to the dimerization of an RTK. The kinase domain auto phosphorylates Tyrosine (Y) on the receptor. This pY allows for the recruitment of other molecules that recognize each other through their domains, creating a cascading effect. Ras is then activated by a GEF which leads to a phosphorylation cascade until ERK is phosphorylated. At that point, ERK enters the nucleus and interacts with transcription factors to produce Cyclin D so that the cell cycle can occur.

What may happen to T cells if an individual had no medullary epithelial cells in the thymus?

Medullary epithelial cells prevent self-recognition and work in negative selection. If there were no medullary cells, self-recognizing T cells would most likely still be removed by AIRE genes in the thymus. However, if there were malfunctions with AIRE genes, the individual would have self-recognizing T cells which would induce autoimmunity.

Describe the Perforin/Granzyme Pathway of apoptosis. What cells utilize this particular apoptotic pathway?

NK cells and Cytotoxic T cells utilize the perforin/granzyme pathway of apoptosis. They use this particular pathway when they have been taken over by antigens, either bacterial or viral. The perforin/granzyme pathway is activated by the presence of the antigen. Perforin is a protein that is secreted by cytotoxic t cells that pokes a hole in their cell membrane. This hole causes the activation of enzyme, known as grandzyme B, which leads to protalysis in the cell. The activation of protalysis causes another protein, caspase 10, to be activated. Once caspase 10 is activated, it causes a cascade of events which eventually leads to the activation of caspase 3, the protein that assures the cell will die.

Explain what protein inhibitors of activated STATs are and the role they play in the JAK-STAT pathway. Make sure to include a description of its structure and its importance.

PIAS play a role in inhibiting STATs specifically. There are four types (PIAS1, PIAS3, PIASx, PIASy) and their mechanism of action is to bind to activated STAT dimers, moving them away from the DNA to prevent them from binding. The structure of PIAS includes a SAP domain for target binding, a RING finger domain which allows proteins to bind to DNA, and a serine-threonine rich domain. This structure prevents the dimer from interacting with DNA, which then can cause DNA to be inaccessible since its deacetylased in the process, and also a SUMO label could be attached to cause STAT to no longer be functional.

Describe the differences between positive and negative selection and what could result if this process is defected.

Positive selection is where cells either undergo apoptosis or are rescued once the TCR is engaged whereas negative selection is when the immune cells have too high of affinity for self antigens so they undergo apoptosis. Both processes involve the removal of potentially harmful cells, and if the process is defective it will result in an autoimmune disorder where your immune cells are attacking self antigens.

How are phosphate groups removed?

Protein phosphatases

What are some similarities and differences of Receptor Tyrosine Kinases (RTKs) and Non-receptor Tyrosine kinases?

RTKs have their own Tyrosine Kinase domain where auto-phosphorylation can occur, while NRTK has no enzymatic component. Instead, NRTKs associate with kinases. For both RTKs and NRTKs, ligand binding dimerizes the receptor which activates kinases (or associated kinases) that phosphorylate each other and go on to phosphorylate downstream substrates.

What are the three ways in which T and B cells convert to active cells?

Reorganization of actin cytoskeleton Activation of transcription factors Synthesizing proteins

4) What activates mTOR and what are 4 results of the activation of mTOR?

Rheb activates mTOR. It is part of the PI3-K downstream pathway. mTOR increases lipid production, increases ribosome biosynthesis, increases mRNA synthesis and increases protein translation.

The egress of lymphocytes from lymphoid tissue is mediated by _________ gradient. Tcell activated by antigen down regulates ___________, which is caused by ___________ expression.

S1P, S1PR1 and CD69

Which of the following GPCR:chemokine pair is not involved in naïve T cell migration through the lymph node?

S1P1:S1P

Which of the following is not a kinase? Lck SLP76 Akt All are

SLP76

List the steps of the JAK-STAT Pathway

Steps: 1. Cytokine binds to receptor 2. JAKs associated with cytokine receptor → Activates and cross phosphorylate each other and then phosphate tyrosine residues on the receptor 3. STAT proteins has SH2 or PTB binding domain that binds to phosphorylated tyrosine residues 4. STAT molecules then themselves have tyrosine residues → JAK and phosphates STAT 5. STAT binds with another STAT to form homodimers or heterodimers 6. Once STATs interact to form dimers, the nuclear localization signal (NLS) will be exposed due to a conformational change 7. NLS signal → STAT dimer can go into the nucleus and act as a TF

Under normal conditions, Ubiquitination is a process that is used to degrade proteins. The HER-2 gene under codes for a tyrosine kinase receptor, which is important for cell growth. When there is a mutation in the HER-2, normal ubiquitination cannot occur, and as a result the cell is able to proliferate uncontrollably, and cancer can result . Please describe the normal ubiquitination process by listing the steps, and then describe the point where a mutation, such as one in HER-2, can lead to uncontrollable cell death as a result of abnormal ubiquitination

Steps: Ubiquitin activating enzyme (E1) Harvest energy released ATP is hydrolyzed to activate ubiquitin molecule Ubiquitin with AMP → high energy molecule that is transferred to activate site of E1 Ubiquitin- conjugating enzyme (E2) The activated ubiquitin is then transferred onto the second enzyme by attached it to a cysteine residue of E2 Ubiquitin- protein ligase (E3) Transfers ubiquitin group to protein target that we actually want to break down into amino acids Ubiquitin forms a bond with lysine residue on target protein Result = protein is degraded The point where, if a mutation occurred, would cause ubiquitination to no longer act normally would be if the cysteine residue on E2 was missing. This would cause the ubiquitin to not be able to bind to E3 from E2 and the marker for degradation would not be recognized by the degrading proteins. This would allow for the proteins to continue to cause cell growth and would eventually lead to cancer.

List the 5 major subsets of CD4 effector T cells, their specific functions and cytokines secreted, what cells they recruit, and what microbes are targeted to kill.

TH1 = secrete IFNy to macrophages to kill intracellular bacteria, do not recruit other cells TH2 = secretes IL-4, IL-5 to bone marrow cells and IL-13 to goblet cells to recruit eosinophils, mast cells, and basophils TH17 = secrete IL-17 to stromal cells, IL-22 to epithelial cells to recruit neutrophils and target extracellular bacteria and fungi. TfH = Secrete IL-21 to B cells with peptide:MHC bound to enhance isotype switching and affinity maturation of B cells or plasma cells to target all types of microbes Treg = inhibits dendritic cells to stop T cell activation and suppress the T cell response

What subset of CD4 T cells targets EC bacteria

TH1 and TH17

What subset of CD4 T cells targets extracellular bacteria?

TH1 and TH17

1. What do you think would happen to a STAT if it undergoes a mutation so it can no longer bind to the phosphorylated tyrosine?

The STAT would no longer be able to bind to the phosphorylated tyrosine, this would lead to downstream events to no longer occur and the STAT transcription factor will no longer lead to the transcription of the wanted gene.

Why are T cells that encounter a lot of self-antigens bad and how does our body prevent such T cells from reaching maturation and being distributed?

The goal of our immune system, and T cells specifically, is to recognize foreign antigens and protect the cells that make up our body from such foreigners. However, self-reactive T cells are not able to distinguish which cells are foreign because they are activated by peptides on MHC molecules that are common in our bodies. This is how autoimmune diseases function; the immune system isn't able to determine what is good and what is bad. Our body prevents these kinds of T cells from circulating through negative selection. If a TCR on a developing T cell is stimulated by a self-antigen, then it is induced to go through apoptosis. This occurs mainly in the thymus, but if a self-reactive T cell does not go through apoptosis, it can be deleted in the peripheral.

SARS-CoV-2 is a virus that attacks the epithelial cells lining your respiratory tract. It binds to ACE2 receptors on these cells to gain entry, where they take over and reproduce. Two weeks after exposure, it is known that antibodies are present in the bloodstream of the previously infected patient. What immune response must have been activated to make this happen?

The immune response that was activated against SARS-CoV-2 was the humoral immune response. The humoral response involves B-cells which when activated form plasma cells which then produce massive amounts of antibodies that are specific to the antigen that the B cell interacted with. After the initial exposure and production of plasma cells, the humoral response also produces immune memory. This occurs because the activated B cells, along with producing plasma cells, produce replicas of themselves which are known as memory B cells. These cells remain circulating through the bloodstream, awaiting a secondary exposure, where they will respond more quickly against the pathogen than the initial exposure.

Why is pre-BCR transiently expressed at the surface during the large pre-B cell stage of its development?

The pre-BCR is present on the surface during this stage to determine whether the H-chain was successful and not self-protein recognizing. A successful pre-BCR mediates the transition from the pro-stage to pre via dimerization signaling, inhibiting further H-chain rearrangement. The transient expression of the pre-BCR is critical for the continuation of the B cell development.

ITAMS motifs are found on proteins on NK cells and macrophages

True

If someone was experiencing a massive infection, they would be able to turn on their anergic B cells in order to help respond to the infection

True

Negative selection takes place in the central lymphoid organs

True

T/F: SCID mice do not have a functional thymus

True

Zap70 conains SH2 doamins

True

What are two ways that protein degradation happens in ubiquitination?

Ub tagged proteins can be degraded by the lysosome or proteasome

Activated ZAP-70 phosphorylates LAT and SLP-76 and initiates which four pathways?

a) Akt leads to increased cellular metabolic pathway b) Vav leads to actin polymerization c) PLC-gamma leads to transcription factor activation d) ADAP enhances integrin adhesiveness and clustering

1. Name and explain 1 of the 4 major parallels between TCR and BCR signaling.

a. One parallel is the functions of tyrosine kinases as signal transduction initiators in the BCR and TCR. Src-family protein tyrosine kinases such as BLK, FYN, and LYN initiate signal transduction by the BCR. They initiate the signaling by binding ITAMS, which are then bound to Syk which is a kinase with a similar function to Zap-70 in TCR signaling. In TCR signaling, LCK or Fyn are also Src-family tyrosine kinases that phosphorylate the ITAMS associated with the TCR. Once the ITAMS on the TCR are phosphorylated by LCK, Zap-70 is activated. Therefore, tyrosine kinases phosphorylate ITAMS to initiate signaling in the TCR and BCR.

1. Explain the importance of the thymus and bone marrow in the context of the experiment with Nude and Scid mice.

a. Scid mice does not have B or T cells due to a deficiency in bone marrow HPC. These mice are defective in the antigen receptor gene rearrangement gene (Rag -/-). Nude mice do not have a thymus due to defective development of the cortical epithelial cells. B cells are present in Nude mice because they mature in the bone marrow, but developed T cells are not present. When the "Nude" bone marrow was transplanted into the Scid mouse, the grafted bone marrow cells (Rag +/+) were able to repopulate in the normal thymus of the Scid mouse. The functional thymus from the Scid mouse was transplanted into the nude mouse (Rag +/+), and the lymphocytes were able to repopulate in the grafted thymus. Therefore, functional bone marrow and a functional thymus must be present for lymphocyte development and proliferation in peripheral organs, but grafted versions of each can be functional in producing T cells.

What do protein kinases do?

activate receptors on the T and B cells that convert extracellular signals into intracellular biochemical events

Which portion of the B cell receptor undergoes gene rearrangement first? A. Heavy chain B. Beta chain c. Alpha chain d. Light chain

answer: A

What does SH2 domain recognize?

phosphotyrosine

Briefly explain what would happen within T cell production when the thymus is removed before and after puberty.

· The thymus is fully developed at birth at humans and the rate of T cell production by the thymus is greatest before puberty. So, if the thymus were removed before puberty, there would be little to no production of T cells and the person would most likely be immunocompromised. The thymus begins to shrink after puberty and the production of T cells is reduced. Therefore, removing the thymus after puberty would have no notable loss of T cell function or numbers and therefore immunity should be sustained throughout life.

In what circumstance does phosphorylation result in a de-activating signal?

· Usually, phosphorylation can make something be in the active state. In relation to the T cell receptor, Csk will phosphorylate Lck and cause it to be in the inactive state. Then, when CD45, a phosphatase, takes off the phosphate that is on Lck, Lck can do its function of phosphorylating the ITAMs on the TCR.

Explain the results of positive selection that is mediated by the thymic cortical epithelial cells and their importance in T cell development

· When the thymic cortical epithelial cell expresses MHC II normally, both CD8 and CD4 T cells are made. If there is a mutation where the thymic cortical epithelial cell is mutated to not have an MHC II complex, there will be no CD4 cells produced and only CD8. They also had a mutant thymic cortical epithelial cell that expressed MHC II but couldn't bind to CD4 cells, and it resulted in only CD8 T cells being produced. These experimental results indicate that not only is the expression of MHC II from the thymic cortical epithelial cells important in T cell development, but also the ability to interact with CD4 in order to allow CD4 to fully develop and mature.