changes in antibodies class switch recombination membrane vs secreted mutation, selection low...
TRANSCRIPT
Changes in Antibodies• Class switch recombination
• Membrane vs secreted
mutation, selection
Low affinity
Highaffinity
• Affinity maturation
IgEConstant region(function)
Variable region(antigen-binding)
Transmembrane& IntracellularDomains
B cell Plasma cell
IgG1
IgEIgM
IgAAID
B Cell Differentiation Pathways
Germinal Center
Activated B Cell
Short-LivedPlasma Cell
Affinity MaturationHypermutation, Selection
Long-LivedPlasma Cell
Memory B Cell
Normal Functions of AntibodiesNeutralization
toxins
viruses
Mast cell
Parasiticworm
inflammation
bacteria
Complement activation
Macrophagebacteria
Opsonization
Toxic granulesForeign/ infected cell
Antibody-dependent cytotoxicity
IgG1
IgE
IgM
IgA
Questions
• Why do IgE and IgG1 differ in abundance?• How do IgE vs IgG1 B cells behave in germinal
centers?• What are possible models leading to the loss
of IgE germinal center B cells?
Questions
• Why do IgE and IgG1 differ in abundance?• How do IgE vs IgG1 B cells behave in germinal
centers?• What are possible models leading to the loss
of IgE germinal center B cells?
Helminth parasite model:Nippostrongylus brasiliensis infection
Serum IgG1 vs IgEInfectionN. brasiliensisL3 larvae
Erazo A. et al. Immunity 2007, 26:191-203.
Cheng L.E. et al. J Immunol 2010, 185:5040-5047.
Questions
• Why do IgE and IgG1 differ in abundance?• How do IgE vs IgG1 B cells behave in germinal
centers?• What are possible models leading to the loss
of IgE germinal center B cells?
IgE vs IgG1 B cells
GFP (IgE)
GFP (IgE)Ig
G1
NP-KLHAlum adjuvantTNP-OVA
Alum adjuvant
N. brasiliensisinfection
Talay O. et al. Nat Immunol 2012, 13:396-404. Yang Z. et al. Immunity 2012, 36:857-872.
Kinetics of IgE vs IgG1 B cells in GCs
N. brasiliensisinfection
Talay O. et al. Nat Immunol 2012, 13:396-404.
Yang Z. et al. Immunity 2012, 36:857-872.
He J.S. et al. J Exp Med 2013, 210:2755-2771.
Questions
• Why do IgE and IgG1 differ in abundance?• How do IgE vs IgG1 B cells behave in germinal
centers?• What are possible models leading to the loss
of IgE germinal center B cells?– BCR signaling
BCR expression in IgE vs IgG1 Germinal Center B Cells
He J.S. et al. J Exp Med 2013, 210:2755-2771.
HA-specific B cells
Questions
• Why do IgE and IgG1 differ in abundance?• How do IgE vs IgG1 B cells behave in germinal
centers?• What are possible models leading to the loss
of IgE germinal center B cells?– BCR signaling– Plasma cell differentiation
IgE+ B cells are Biased Toward Plasma Cell Differentiation
in vivo
NP-KLHAlum adjuvant
subQ 8 days
in vitro
NaïveB cells
Anti-CD40
IL-4&spleen+
4 days
Draining LNs (FACS)
Yang Z. et al. Immunity 2012, 36:857-872.
Cell-Intrinsic Increase in IgE+ GC B Cells Caused by Blimp-1 Deficiency
CD45.2 GC B / CD45.1 GC B
CD45.2 naive B / CD45.1 naive B
Yang Z. et al. Immunity 2012, 36:857-872.
Blimp-1 is a transcription factor needed for plasma cell differentiation
Shorter LifespanReduced Affinity
Yang Z. et al. Immunity 2012, 36:857-872.
Why IgE B cell lifespan and affinity may be limited
Neutralization
toxins
viruses
Mast cell
Parasiticworm
inflammation
IgG1IgE IgA
Systemic IgE activation
IgA Background
• IgA is secreted in mucosal tissue and is transported across mucosal epithelial barriers by the poly-Ig receptor
• In the gut, class switch to IgA occurs in Peyer’s patches and Isolated Lymphoid Follicles
• IgA plasma cells traffic via the blood back to mucosal sites
• IgA deficiency is very common (~1 in 500) but is asymptomatic in a majority of individuals
IgA: Questions
1. What about gut bacteria induces an IgA response?
2. Are IgA-secreting plasma cells long-lived or short-lived?
3. Do IgA responses exhibit immunological memory?
4. What effect does IgA have on bacteria in the gut?
Question 1: What about gut bacteria induces an IgA response?
Question 1: What about gut bacteria induces an IgA response?
Approach 1: Controlled antigen delivery to the mucosal immune system
HA107 is an E coli auxotroph for m-diaminopimelic acid (DAP) and for D-alanine (required for peptidoglycan biosynthesis and not made by host)
Reversible microbial colonization of germ-free mice
Hapfelmeier et al. Science 328: 1705-9, 2010
Most IgA plasma cells in gut are dependent on gut bacteria
HA107 gavaged 6 times over 14 days; IgA plasma cells (green) evaluated after 4 weeks total (blue: DAPI staining of nuclei)(ASF: altered Schaedler flora, a mixture of 8 mouse gut bacteria that creates a relatively stable community)
Hapfelmeier et al. Science 328: 1705-9, 2010
Threshold for IgA response to E coli K-12
Hapfelmeier et al. Science 328: 1705-9, 2010
Question 1: What about gut bacteria induces an IgA response?
Hapfelmeier et al. Science 328: 1705-9, 2010
Live bugs induce IgA >10X better than heat-killed bugs
Question 2: Are IgA-secreting plasma cells short-lived or long-lived?
Hapfelmeier et al. Science 328: 1705-9, 2010
Question 2: Are IgA-secreting plasma cells short-lived or long-lived?
What does this result imply for the longevity of IgA plasma cells?
Hapfelmeier et al. Science 328: 1705-9, 2010
Question 2: Are IgA-secreting plasma cells short-lived or long-lived?
What does this result imply for the longevity of IgA plasma cells?
Question 3: Do IgA responses exhibit immunological memory?
Approach 2: Deep sequencing of gut IgA+ plasma cells
Deep sequencing of gut IgA+ plasma cells
Lindner et al. J Exp Med 209: 365-77, 2012
-Gut IgA plasma cells are highly polyclonal with a subset of highly expanded clones-The frequency of somatic mutations goes up with age
Question 3: Do IgA responses exhibit immunological memory?
What can be done to look at a memory response in this system?
Question 3: Do IgA responses exhibit immunological memory?
Lindner et al. J Exp Med 209: 365-77, 2012
Lindner et al. J Exp Med 209: 365-77, 2012
Plasma cells are killed off with Bortezomib, a proteasome inhibitor (used in multiple myeloma patients)
Question 3: Do IgA responses exhibit immunological memory?
Lindner et al. J Exp Med 209: 365-77, 2012
Gut IgA plasma cells show considerable clonal overlap before and after killing plasma cells with Bortezomib
Lindner et al. J Exp Med 209: 365-77, 2012
Question 4: What effect does IgA have on bacteria in the gut?
Approach 3: Genetic defect in the IgA response
(Activation-induced cytidine deaminase, AID, is required for somatic mutation AND class switch)
AID-/- mice exhibit a dramatic expansion of Peyer’s patches and ILFsAID+/- AID-/-
3 wksof age
20 wksof age
Fagarasan et al. Science 298: 1424-1427, 2002.
AID-/- mice exhibit a dramatic expansion of Peyer’s patches and ILFsAID+/- AID-/-
3 wksof age
20 wksof age
Fagarasan et al. Science 298: 1424-1427, 2002.
Why is there a large expansion of germinal centers in the mucosal lymphoid tissues?
Changes in representation of different gut bacteria in AID-/- mice
Fagarasan et al. Science 298: 1424-1427, 2002.
Somatically mutated IgA restricts the numbers of bacteria in the gut
Wei et al. Nature Immunology, 2011
AID G23S: 9-15x lower somatic mutation; equivalent fraction of plasma cells that are IgA
IgA restricts the numbers of Segmented Filamentous Bacteria in the small intestine
Suzuki et al. PNAS 101: 1981-1986, 2004
Upper Small Intestine
Lower Small Intestine
Question 1: What about gut bacteria induces an IgA response?
Segmented filamentous bacterium
Ivanov et al. Cell 139: 485-498, 2009
Question 1: What about gut bacteria induces an IgA response?
Different components of the gut microbiome may differ greatly in their localization within gut, invasiveness, ability to induce inflammation, etc. (“pathobionts”)
Question 1: What about gut bacteria induces an IgA response?
Approach 4: Separate bacteria that are coated with IgA from those that are not by flow cytometry
Sorting IgA-coated bacteria
Palm et al. Cell 158: 1000-10, 2014
MICE
Sorting IgA-coated bacteria
Palm et al. Cell 158: 1000-10, 2014
ICI: relative abundance IgA+/ relative abundance IgA-
Sorting IgA-coated bacteria from people with Inflammatory Bowel Disease
Palm et al. Cell 158: 1000-10, 2014
Consortia of IgA+ vs. IgA- microbes
Palm et al. Cell 158: 1000-10, 2014
Consortia of IgA+ vs. IgA- microbes: stable short-term colonization of mice
Palm et al. Cell 158: 1000-10, 2014
Consortia of IgA+ vs. IgA- microbes: different degrees of IgA induction
Palm et al. Cell 158: 1000-10, 2014
Consortia of IgA+ vs. IgA- microbes: invasion of the mucus layer by the IgA+ bugs
Palm et al. Cell 158: 1000-10, 2014
Consortia of IgA+ vs. IgA- microbes: inflammatory action
Palm et al. Cell 158: 1000-10, 2014
Somatically mutated IgA limits number of pathogenic bacteria that reach MLN
Wei et al. Nature Immunology, 2011
Yersinia enterocolitica numbers detected in mesenteric LN