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73 Cards in this Set
- Front
- Back
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Types of antigen displayed on CLass II MHC:
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-Intravesicular
-Extracellular |
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Type of cell that responds to Class II MHC / Ag:
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Thelper CD4+
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Thelper becomes:
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either Th1 (IL12) or Th2 (IL4)
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Thelper 1 secretes:
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-IFN-y
-TNF-a |
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Cells stimulated by Th1 cytokines:
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-Macrophages
-Bcells |
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Th1 does what to macrophages:
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Activates them to increase their ability to phagocytose and kill
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Th1 does what to Bcells:
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Stimulates isotype switching to IgG1 and IgG3
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Th2 cells secrete:
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IL4, 5, and 10
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Th2 cytokines stimulate what cells?
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B cells
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What does Th2 stimulation of Bcells do?
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Stimulates isotype switching to IgG2, 4, and IgA and IgE
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Viruses are presented by what MHC
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MHCI
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what cells respond to viral antigens on MHC I?
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CD8+ Tc cells
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What do CD8+ Tc cells do?
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Kill the infected cells either independently or with Thelper help
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When is CD4+ Thelper help needed for CTL differentiation?
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When the antigen presented on MHCI is in too low of concentration.
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What are the functions of class switching to IgG1 and IgG3 stimulated by Th1 cells?
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To function as opsonins and activate complement.
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What marks a Bcell as mature?
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The presence of both IgM and IgD
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What are the 2 phases of antibody response?
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-Primary
-Secondary |
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When does a primary Ab response occur?
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Upon initial infection
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When does a secondary Ab response occur?
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Upon repeat infection
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Where do naive Bcells first see antigen in a first infection?
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In lymph nodes, out near the cortex.
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What happens to Bcells upon initial recognition of antigen?
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They become activated if sufficient costimulatory molecule is expressed on the APC
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What happens to activated Bcells?
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They secrete antibody in peripheral lymphoid tissues.
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How many days usually follow the initial infection before antibody secretion begins?
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5-10 days
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What is the prominent antibody that is secreted in a primary response?
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IgM > IgG
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What is the antibody affinity like in a primary response?
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Lower than average, and more variable.
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How many days usually follow a repeat infection before antibody secretion begins?
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only 1-3 days
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What is the peak response in a secondary response compared to primary?
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Much greater
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What is the predominant antibody made during a secondary response?
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IgG, or IgA/IgE in certain situations.
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What is the antibody affinity like in a 2ndary response?
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Higher than average affinity.
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Why is affinity higher in a secondary response?
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Because of affinity maturation.
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Are cell-surface associated immunoglobulins capable of signal transduction?
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No
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What molecules transduce the signal into Bcells?
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Ig-alpha and Ig-beta
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What happens when Ig-a and Ig-B transduce a signal into the Bcell?
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Tyrosine phosphorylation cascades which cause enzyme upregulation and transcription factor stimulations.
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What are the steps in Bcell activation?
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1. C3d binds microbe
2. BCR (Ig) binds microbe 3. Bcell CR2 binds complement coating the microbe |
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What is the purpose of the complement protein C3d coating microbe and binding to the Bcell's CR2 receptor?
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It serves as the 2nd signal for Bcell activation.
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What are the main consequences of Bcell activation during a primary infection?
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1. Clonal expansion
2. Increased expression of B7 and cytokine receptors 3. Migration out of lymphoid follicles to interact w/ Th 4. Secretion of low amts IgM |
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Why would you want activated Bcells to express more B7?
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So they can stimulate Thelper cells more effectively - remember Bcells act as APCs too
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What does T:B interaction during a primary infection consist of?
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1. Activated Bcells migrate from follicle to paracortex
2. Present Ag to Thelper cells, along w/ B7 to CD28 |
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What is the Thelper response to antigen presentation by Bcells?
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Proliferation, differentiation, and depending on the cytokine environment C' activation/inflammation or IgE class switching.
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What do activated Bcells do after interacting with Tcells near the paracortex?
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They migrate back into the follicle.
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How can Bcells act as APCs?
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They swallow up the microbes that crosslink the surface Ig's by receptor mediated endocytosis.
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What MHC do Bcells present antigen on?
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MHCII
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What is needed for Bcells to properly activate Tcells?
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1. Antigen presentation
2. B7 binding to CD28 |
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Can B:T interaction occur during a primary antibody response?
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No; there are not enough B clones proliferated yet to present sufficient amt of Ag to Tcells to activate them.
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What do we call the space between a T and Bcell during interaction?
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Immunological synapse
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What is the key molecule that is expressed by activated Tcells in response to Bcell antigen presentation?
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CD40L
-cytokines secreted |
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What happens when the CD40L on Tcells engages with the CD40 on Bcells?
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Cytokines from the Thelper cell cause Bcell proliferation and differentiation
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What is the principal effector function of IgM?
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Complement activation
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What are the 3 functions of IgG1 and IgG3?
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1. FcR-dependent phagocytosis
2. Complement activation 3. Neonatal immunity |
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What are the 2 principal functions of IgE?
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1. Immunity against helminths
2. Mast cell degranulation |
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So the hypersensitivity that IgE is involved in is:
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Immediate Hypersensitivity Type I
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What is the principal effector function of IgA?
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Mucosal immunity
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What are the 3 changes that can occur to an antibody's structure during its lifetime?
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1. Affinity maturation
2. Switching from membrane to secreted form 3. Isotype switching |
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Where does affinity maturation occur?
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In Bcell germinal centers
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What is the basis of affinity maturation?
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In germinal centers, only the b-cells with high affinity for the Ig antigen survive
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What cells present Ag to activated Bcell clones in germinal centers following an antigen stimulation?
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Follicular dendritic cells
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Toward the end of antibody production when lots of Ab-Ag complexes are around, how does the Ab reaction stop?
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By binding of Ab-Ag complex Fc regions to FcR's on Bcells
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Is T:B interaction required for antibody secretion?
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No
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How can Bcell production be stimulated in the absence of Tcells?
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By Thymic-Independent antigens
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What are the types of Thymus-Independent antigens?
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TI-1: polyclonal activators of Bcells at high concentrations
TI-2: polysaccharide activators with repeating subunits (epitopes) |
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What do Polyclonal Bcell activators stimulate at LOW concentrations?
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Specific antibody
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What types of Bcells are stimulated by polyclonal activators?
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Both immature and mature Bcells
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What is the best example of a TI-1 polyclonal activator?
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LPS
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What type of antibody is secreted in response to a TI-1?
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IgM
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What type of activation results from polysaccharide epitopes?
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Monoclonal
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What is the best example of a TI-2 epitope?
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Baccterial capsular polysaccharide
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What type of antibody is secreted in response to a TI-2 stimulation?
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IgM
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Does isotype switching of antibody occur in response to TI-1 antigens? TI-2?
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TI-1: yes
TI-2: NO |
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Does affinity maturation occur for TI-1 antigens or TI-2?
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TI-1 only
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Is there a 2ndary response upon repeated exposure to TI-1 or TI-2 antigens?
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TI1: yes
TI2: only with certain epitopes |
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Where are isotypic differences on antibodies found?
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In the Fc regions of the heavy chain
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Where are allotypic differences on an antibody found?
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In the Fc region, but these are only single AA differences
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Where are idiotypic differences found?
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At the variable regions of both heavy and light chains.
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