Signaling of Naive T & B Cells Flashcards
Quiz 4
When are transmembrane receptors needed during signaling
Needed when signals can’t cross the membrane on their own
Describe the function of receptor tyrosine kinase (RTK)
-upon binding, activates a kinase (separate protein)
-upon binding of ligand, it will dimerize and then autophosphorylates
What are two examples of proteins that propagate signal
-kinases
-scaffold proteins
What domain in RTK’s play a key role in propagating signal
SH2 (how it phosphorylates tyrosine)
What does a scaffold protein do
-Activation of a protein kinase results in phosphorylation of a scaffold
-phosphorylated scaffold requires signaling proteins and brings them closer together
-also brings them to the membrane
What changes do most signaling pathways end
-Changes to transcription factors
-Rewires the cells trancriptome/proteome
-can range from simple (few genes) to complex
What are two ways signaling pathways are turned off
-phosphatases (dephosphorylate)
-ubiquitin (degradation of receptor)
What are three components of the T cell Receptor (TCR)
-alpha beta receptor (insufficient for signaling)
-CD3 complex
-gamma domain (completely intracellular)
-Positive, transmembrane pieces
Where are ITAM (Immunoreceptor Tyrosine-based Activation Motifs) found
-Found in signaling proteins for
-Tcells
-B cells
-NK
-Phagocytes
-Ab sensing (Fc receptor)
Explain the activation of the TCR
-Requires co-receptor (CD4: MHC II Th and CD8: MHC I cytotoxic)
-Binding leads to ITAM phosphorylation
-Recruite downstream proteins
What is Lck
-SCR-family kinase
-boudn to CD4 or CD8
-Phosphorylates ITAMs
-Kept inhibited until activated
What is PIP3
membrane bound and forms both a soluble and membrane-bound signals after PLC cleavage
What are the 2 outcomes of PLC cleavage of PIP3
-Ras signaling
-Induces CA2+ release
What is an immune synapse
-TCR-MHCII complex
-Integrins
What are BCR (B-cell Receptor)
-antibodies are screted (need to become receptors)
-Antibody is generated with a transmembrane domain
-Interacts with Igalpha and Igbeta (help in trafficking and contains ITAMS
Explain how BCR binding activates SRC-family kinases
-free antigen binds with multivalency (multiple epitopes on antigen: CROSSLINKING)
-leads to phosphorylation of ITAMs on B-cell receptor tails by SRC-family kinase
-Sky binds to double phosphorylated ITAMs and is activaed on binding
What is an alternative method of B-Cell activation
-using co-receptor
-CD21 (CR2) binds a C3 freagment
-Antigen + complement= activation
What are two receptors that regulate antigen receptor signaling
-APCs can express co-stimulatory molecules (induced by PRR/ cytokine signaling)
-Robust T cell receptor activation requires (antigen presentation on MHC and co-stimulatory signal)
What is the role of CD28
-on naive T cell, recognizes B7.1 or B7.2
-B7 is expressed only on ‘activated’ APC
-Recognition by CD28 leads to high PIP3 (PIP3 is also induced by TCR)
-The two activated lead to max PIP3
What are two things required for T-cell activation
-TCR
-CD28
What is CD40
-TNF-superfamily receptor
-very different from RTK’s
-When not activated (TRAF molecules UB-ate NIK and NIK degraded)
What happens upon activation of CD40
-TRAF is degraded
-NIK phosphorylates the IKK
-IKK activates NFkB
What happens when NFkB is activated by CD40
-Non-canonical NFkB activation pathway
Why do activated T cells start expressing inhibitory receptors
Prevents over-activation (can even inhibit other T cells)
What happens when you inhibit inhibitors
-checkpoint blockade
-cancer treatment
-leads to autoimmune diseases
What is positive selection
signal for survival only if receptor WEAKLY binds self (T cells)
What is negative selection
eliminate lymphocytes with receptors that STRONGLY bind self (B and T cells)
What is the generaly process of lymphocyte development
-stem cells made w/ bone marrow
-stem cells differentiate based on signals
-develop in central lymphoid tissues (B cells stay in bone marrow and T cells move to thymus)
-migrate to peripheral lymphoid tissues (lymph nodes, spleen, and mucosal lining)
What is the main role of stromal cells
-secrete chemokines
-retain pre-C cells
-if pre-B cell unbinds stromal cells, will migrate back to stromal cells by sensing CSCL12 (follows chemokines back to cell to prevent pre-B cell from hurting cell)
Describe the phases of B cell development
-stem cell
-early pro-B cell (D-J rearranging ‘H-chain’)
-late pro-B cell (V-DJ rearranging ‘H-chain’)
-Large pre-B cell (VDJ rearranged ‘H-chain’)
-small pre-B cell (VDJ rearranged ‘H-cahin’ V-J rearranging ‘L-chain’)
-Immature B-cell (VJ rearranged ‘L-chain’)
-Mature B cell (VJ rearranged ‘L-chain’)
How can a B cell Test that a heavy-chain protein is ‘functional’
-V(D)J recomb. can lead to non-functional proteins
-Express the recombined heavy chain + a surrogate light chain
-The surrogate light chain is non-rearranging
What is a surrogate light chain
-look like ligh cahin w/ no recomb.
-just a test of heavy chain
What is surrogate light chain testing
-can heavy chain bind light chain
-does it signal correctly
-if yes: goes from Pro-B to Pre-B
How does surrogate light chain test
-regions of gamma 5 _VpreB interact between neighbors
-activates ITAMs
What happens if the BCR fails surrogate lgith chain test
-first, try again
-if fails again, goes to apoptosis
What is allelic exclusion
-one antibody goes to one specific B cell
-one T-cell goes to one specific TCR
What happens after the transition to large pro-B cell
-cells undergo multiple divisions (therefore there is a same exact H-chain with different lgiht chains for each B-cell)
-then start light-chain rearrangement
-one pro-B to many B cell Ab’s
How often can the light chain rearranging
-can reoccur if leads to an unproductive version
-as long as there are V- and J-regions to use
-can even switch to other chromosome
-allelic exclusion
-if fail, apoptosis
What is tolerance
removal of autoreactive B cells/ T cells
What is ideal for a mature B-cell
-has central tolerance (can’t bind itself
-no self reaction
What happens if the B cell becomes multivalent self molecule
-receptor editing
-sense a self-antigen (arrest development, start VJ rearrangement again)
-once a new one is formed, test again
what is anergy
a state of ‘permanent’ non-responsiveness to antigen
what is ignorance
B-cell never encounters antigen (or usually too weak of binding)
How do T cells keep B cells alive
Survival signals, B cells need these signals or they die rapidly
Describe role of B-1 in innate immunity
-recognize carbohydrates (bacterial capsule)
-don’t adapt after infection (always make constitutive Ab)
-Don’t need Th activation
What signaling in thymus commits progenitor to T cell development
Notch signaling
What are the two components of thymus anatomy
-outer: cortex (thymocytes)
-inner: medulla (epithelial cells)
What T cells express CD4
helper T cells (MHC II)
What T cells express CD8
cytotoxic T cells (MHC I)
Explain process of alpha:beta T cell developmet
-thymocytes start DN and CD3- (double-negative)
-Become CD3+ and double positive (CD3 is the TCR co-receptor)
-eventually differentiate and express only CD4 or CD8
Explain Tcell development during double negative stage
-move throughout the thymus
-moves cortically at the beginning
-during DN4, proliferates
-then moves to the medulla
Which chain of the T cell rearranges first
-the beta chain
How is the beta chain protein tested
-it uses an alpha chain surrogate
-beta chain can rearrange if needed
-successful signaling leads to proliferation and shuts down beta chain rearrangement (Now T cell transition to double-positive)
Describe T cell development during double-positive stage
-after proliferation in DN4 Tcell expressed CD4 AND CD8 and starts alpha chain rearrangement
How is the testing of TCR different from testing of BCR
-for the TCR you want to see binding if there is no signaling it wants to die
What happens if the TCR can’t bind MHC:peptide
rearrange the alpha-chain until it works (as long as you have V- and J-)
explain negative selection for TCR
-don’t want T cells to attack host
-if TCR bind MHC:peptide too well (apoptosis)
-just like B cells (Central tolerance)
What is AIRE
-Transcription factor
-makes a bunch of proteins
-These proteins present on MHC’s as peptides
How do thymus cells express all self peptides
-first, they can’t (hence peripheral tolerance)
-uses AIRE
What is peripheral tolerance
-removal of lymphocytes that recognize self in peripheral lymphoid tissue
-either induce cell death OR energy
How does a CD8+ T cell know whether an epithelial cell is displaying a MHC-I with a peptide from self vs. virus
inflammatory signal: tight ninding w/ no signal recognize as self
