Midterm 2 Concepts Flashcards
MHC Class 1 Loading Pathway
MHC1 is unstable w/o a bound peptide, thus managed by chaperone proteins in the ER
1) Degradation of proteins in cytosol by proteasome
2) Transportation of peptides fr cytosol into ER by TAP proteins
3) Peptides load into ER, which undergoes conformational change to become folded / stabilized
4) MHC1 is released from ER to go to surface for expression
TAP KO still allows MHC to leave ER but bc will be in unfolded / unstable conformation, will most likely degraded by proteasome before it reaches the surface (unless it encounters an exogenous peptide)
MHC Class 2 Loading Pathway
MHC2 molecule in ER will be stabilized with the Invariant chain, which mimics a peptide to allow proper folding but also prevents other peptides from binding
1) Degradation of proteins occurs in the same vesicle as the MHC by endosomes ;; this process also degrades the Ii and leaves behind CLIP (which prevents other peptides from loading)
2) HLA-DM will bind to MHC2 and release CLIP
3) Antigen peptides will bind to MHC2 and then will travel to the cell surface
Steps of signal transduction
1) TCR + CD4/8 will bind peptide:MHC complex
2) Lck will phosphorylate ITAMs on CD3 complex
3) ZAP-70 binds to P-ITAMs on CD3-zeta chains
4) Lck phosphorylate and activate ZAP-70
5) ZAP-70 phosphorylates SLP-76 and LAT, forming a complex
- LAT is more involved with the PLC-gamma pathway
- SLP-76 is more involved with the RAS/MAP pathway
6A) PLC-GAMMA PATHWAY: PLC-gamma will cleave PIP2 into DAG and IP3
- IP3 is more involved with the Ca2+ mediated pathway → will bind to and open calcium channels, which will activate calmodulin, which will bind to the Ca2+, which will activate calcineurin, which will dephosphorylate NF-ATp, which will activate transcription factor NF-AT to enter the nucleus and activate transcription
- DAG is more involved with the PKC mediated pathway → will interact with calmodulin (resulting from IP3 pathway) and trigger protein kinase C, which will activate IkB kinases, which will cleave off the inhibitory IkB off of NF-kB, which will activate NF-kB to enter the nucleus and activate transcription
6B) RAS/MAP PATHWAY: GTPase dependent pathway bc dephosphorylates Ras, which will activate it, which will activate the MAP kinase pathway, which ultimately generates the transcription factor AP-1 which will enter the nucleus and activate transcription
7) Transcription leads to alterations in gene expression, especially through the IL-2 gene promoter
Immunosuppressive drugs (eg FK506 and cyclosporin) block NF-AT activation by inhibiting calcineurin; used in preventing transplant rejection.
What’s the importance of Nude v Scid mice?
Mutations of the Thymocyte, specifically SCID: loss of DNA-PK = no VDJ gene rearrangement = no B or T cell development
Mutations of the Stromal Cells, specifically NUDE: loss of FoxN1 trans.factor = defective thymic stroma = no T cell development
Bone marrow from Nude mouse injected into Scid recipients → THYMIC RECONSTITUTION (recovery of T cells) bc T cells originate in the bone marrow, which will still have DNA-PK
Graft of thymic rudiment from Scid mice into Nude recipients → THYMIC RECONSTITUTION bc while Nude mice don’t have the structure to develop T cells, they still have all the machinery, so when the graft is done, they can begin making T cells again
Explain the Fas/L pathway
Both Fas and Fas ligand (FasL) are slowly upregulated on activated T cells
Binding of Fas to FasL induces a conformational change in Fas, which then binds death domain-containing adaptor proteins, which will then recruit and active caspase 8, which will cleave caspase 3, which will cleave I-CAD (the inhibitor of CAD), which allows CAD to enter the nucleus and cleave DNA, which triggers apoptosis
Mutations of this pathway lead to lymphoproliferative and autoimmune disorders
WHAT HAPPENS IF YOU CROSS THE TCR TRANSGENE ONTO A DIFFERENT MHC HAPLOTYPE?
If Tg and MHC are not the same haplotype, no maturation of SP T cells mature
If Tg and MHC are the same haplotype, then only one type of SP T cell matures
- Types of SP maturation is dependent on what type of T cell the Tg is specific for (ie OT1 is specific for MHC Class 1, thus will generate CD8 ;; versus AND is specific for MHC Class 2, thus will generate CD4)
The 4 Steps of Killing by Inducing Apoptosis for NK Cells and CTLs
1) Conjugate formation: done with any inter-cell interaction and used to determine whether a stronger response is necessary → prolonged contact leads to polarization of MTOC / golgi apparatus / and secretory granules towards the target cell ;; also leads to formation of an immunological synapse
- Immunological synapse: helps promote focused release of effector molecules onto the target cell
2) Membrane attack: upon contact with the target cell membrane, perforin monomers undergo conformational change, insert themselves into the membrane, and polymerize with other monomers to form a pore that pokes holes into the target cell membrane
3) Dissociation: once granule exocytosis occurs, the CTL/NK Cell will dissociate from the target cell and search for more target cells
- Granule exocytosis: introduction of granules into the target cell via the pore formed during membrane attack
4) Target cell destruction via Apoptosis: granzymes will cleave caspases to trigger apoptosis
Sequence of events in T-B collaboration
Antigen binding to BCR provides Signal 1 to Naive B cell → antigen is then internalized, processed, and displayed on MHC for T cell recognition
CD4 T cells recognize peptide:MHC complex on B cells and provide Signal 1 to T cell
interaction between B7/CD28 provide signal 2 to fully activate T cell
T cell activation leads to upregulation of CD40/L interactions, which provide Signal 2 to B cells
Cytokine production by CD4 also helps to activate B cell and direct class switching
B cell proliferates and differentiates into Ab secreting B cell (aka plasma cell) ;; now an Activated B cell → Cells w/in a single B cell clone can produce Ab with the same Ag binding site but diff constant regions
