Transcript Ronald van Ree

Mechanisms of sensitization, disease development and desensitization:
towards novel approaches for prevention and therapy
Ronald van Ree
Academic Medical Center, Amsterdam
Priorities for allergy/asthma research
Immunology: B-cells and antibodies
Immunotherapy: mechanisms and monitoring
Atopic march: eczema → asthma → rhinitis → asthma?
B-cells and antibodies
Interaction between allergen and IgE is at
the basis of allergy and (extrinsic) asthma.
Exposure to allergen results in:
no response?
protective response (“active tolerance”)?
sensitization?
+/- symptoms?
How is the process of B-cell activity towards or away from
allergic inflammation regulated?
genetic factors
exogenous factors
(environment incl. allergens
infections, diet, lifestyle)
DC
naïve
Th
Th2
IFNγ
Th1
no allergy
IL4/IL13
Th2
Th2
Th1
Ig?
B-cell
Th1
IgM
B-cell
IgE
B-cell
allergy
genetic factors
exogenous factors
(environment incl. allergens
infections, diet, lifestyle)
DC
Scheme of a simple Th1-Th2
disbalance to distinguish
between allergic and non-allergic has actually been
dismissed as being too simple.
naïve
Th
Th2
IFNγ
Th1
no allergy
IL4/IL13
Th2
Th2
Th1
Ig?
B-cell
Th1
IgM
B-cell
IgE
B-cell
allergy
genetic factors
exogenous factors
(environment incl. allergens
infections, diet, lifestyle)
DC
naïve
Th
Treg
Th1
?
no antibody
response?
IgG? IgA?
Th2
IFNγ
IL4/IL13
Th1
IL10 and/or
TGFβ Treg
IgG/A?
B-cell
no allergy
healthy non-atopic?
Th1
Th2
Th2
IgM
B-cell
IgE
B-cell
allergy
genetic
factors
Questions
and
Discrepancies
exogenous factors
• healthy immune response against allergens: Treg/IL10/TGFβ or Th1/IFNγ or both?
• do B-cells of non-atopic individuals ignore allergens or(environment
produce IgG/IgA
incl. antibodies?
allergens
• Is this different for low-exposure allergens (e.g. pollen and
mite) and
highinfections,
diet,
lifestyle)
exposure allergens (e.g. cat, bee venom and occupational allergens)?
DC
naïve
Th
Treg
Th1
?
no antibody
response?
IgG? IgA?
Th2
IFNγ
IL4/IL13
Th1
IL10 and/or
TGFβ Treg
IgG/A?
B-cell
no allergy
healthy non-atopic?
Th1
Th2
Th2
IgM
B-cell
IgE
B-cell
allergy
genetic factors
exogenous factors
timing/dose/context of
allergen exposure
DC
Th1
naïve
Th
modTh2
IgE?
B-cell
IgG4
B-cell
no allergy
IgG1
B-cell
Th1
IL4/IL13
Th2
Th2
modTh2
IL10
IgM
B-cell
IgE
B-cell
allergy
healthy atopic (or atopic treated by immunotherapy) and non-atopic?
genetic factors
exogenous factors
Questions and Discrepancies
• is a modified Th2 response in atopic individuals IgG4 without IgE
or with (little/harmless) IgE?
of Th2?
• is there an early-life window of opportunity for inducingtiming/dose/context
the protective modified
allergen
exposure
• why are IgG4 responses to allergens higher in atopics than
in non-atopics?
• atopic: predisposition to produce IgE and high IgG4?
non-atopic: no tendency to develop IgE and only low IgG4?
DC
• atopic background seems to be less important for IgE/IgG4 production in case
of high exposures: cats, bee venom, occupational allergens, parasites.
Th1
naïve
Th
modTh2
IgE?
B-cell
IgG4
B-cell
no allergy
IgG1
B-cell
Th1
IL4/IL13
Th2
Th2
modTh2
IL10
IgM
B-cell
IgE
B-cell
allergy
healthy atopic (or atopic treated by immunotherapy) and non-atopic?
High early exposure to cat allergen is protective
Allergy (sensitization)
IgG (exposure / protection)
Increased exposure to cat allergen
Lancet 2001 ; Tom Platts-Mills et al.
Why are IgE responses always so low compared to IgG responses?
Half-life of IgE is very short but this can not explain the 1000-fold
difference in serum titers.
A major cause most likely is the poor generation of memory B-cells
for IgE caused by inefficient processing of mRNA for membrane IgE.
Circulating IgE is derived from long-lived plasma cells hiding in survival
niches like the bone-marrow and inflammatory sites.
Two situations:
• low allergen exposure (e.g. pollen/mite)
i.e. a weak Th2 response that will not effectively induce a germinal
center necessary for induction of memory B-cells
• high allergen exposure (e.g. cat, bee venom)
i.e. a strong Th2 response that will a generate mature germinal center
facilitating induction of memory
From: Aalberse RC et al.
J Allergy Clin Immunol. 2004 May;113(5):983-6.
Low exposure situation: no memory only plasma cells
plasma cells
Atopics respond with all three but IgG is not protective under these conditions
Non-atopics only make a little IgG / are hypo-responsive overall compared to
atopics.
From: Aalberse RC et al.
J Allergy Clin Immunol. 2004 May;113(5):983-6.
High exposure situation: memory generation for IgG but not for IgE
plasma cells
Poor expression of membrane form of IgE
favors apoptosis resulting in poor memory
This also reflects the situation during allergen-specific immunotherapy
For primary prevention it is of the greatest importance to
investigate the dose-response relation between allergen
and (the quality) of the immune response.
The window of opportunity is of great importance.
A high-dose protective effect as observed for cat has
so far not been found for house dust mite. For food
allergens this is even more debated.
The outcome has very significant public health impact.
“Promote cats and peanut butter sandwiches early on or not?”
What is needed to study the dose-response relation
between allergen exposure and (the quality of) the
immune response?
• Analysis of (existing) birth cohort samples for IgG and IgA
responses. In most cases only IgE has been measured.
Multiple time points in first year of life are required. Multiplex
systems now allow in detailed analysis with limited sample.
• Analysis of (existing) birth cohort samples for mRNA profiling
• In vitro cellular analyses to study the process of immune
skewing, preferably in an allergen specific fashion.
• Mouse models that go beyond the ovalbumin model by
using real allergens.
Regulatory B-cells, a missing link?
exogenous factors
genetic factors
(environment incl. allergens
infections, diet, lifestyle)
immature
B-cell
Breg
CD1dhiCD5+
major source of IL10
promote Treg development
memory
B-cell
plasma
B-cell
In several mouse models of auto-immune
diseases an anti-inflammatory (protective)
role has been established for regulatory
B-cells. Do they play a protective role in
allergy/asthma. If so, how can they be
promoted?
The quality of IgE antibodies
Do they always translate into clinical allergy? No
There are several examples of IgE responses
that are without clinical relevance, i.e. the ones
observed during parasite infections, the ones
directed to plant glycans and the ones observed
during successful immunotherapy.
Tregs or Th1 cells can not explain the lack of biological activity.
The explanation can also not (always) simply be found in
a protective effect of IgG4 (“blocking antibodies”).
How is the biological activity of IgE assessed?
Stripped basophil protocol
basophils from
non-atopic donor
stripped basophils from
non-atopic donor
lactic acid treatment:
removal of IgE
basophils re-sensitized
with IgE under study
incubation with serum:
sensitization with IgE
Allergen-specific IgE from parasite-infected children lacks activity.
This is not explained by high allergen-specific IgG4 titers
specific IgE
Gabonese (pink) vs Dutch (green)
(n=16)
(n=7)
35
% histamine release (SE)
mean (SE) of anti-mite IgE in IU/ml
40
30
25
20
15
10
5
80
60
a-IgE
mite
40
a-IgE
mite
20
0
0
0.1
Gabonese
Dutch
10
ng/ml
What explains the poor biological activity?
1000
IgE antibodies against plant N-glycans have the same
poor biological activity
% histamin release
60
transgenic human
lactoferrin
40
native human
lactoferrin
20
rPhl p 5
0
0.0001
0.01
1
100
10000
concentration (ug/ml)
An explanation needs to be found why some IgE antibodies are
poor inducers of mediator release, i.e. without clinical relevance.
What is different about these type of IgE antibodies?
Lower affinity? Something else?
Is this also observed during immunotherapy where IgE antibodies
are persistent but skin reactivity clearly decreases.
Are these IgE antibodies the same as before the start of therapy
or are they (partly) newly formed IgE antibodies.
B-cells and antibodies have not received the attention
they deserve compared to T-cells. They do however
produce the antibodies that cause the disease!!
Reasons to study IgE/IgG/IgA antibody responses:
• They are a good read-out of the nature of the immune response
• It needs to be established when/why they are clinically relevant,
i.e. either disease-inducing (IgE) or protective (IgG/IgA).
• Is induction of IgG/IgA before IgE a protection against future
sensitization?
• What is the difference between IgE from direct (μ to ε) and from
indirect (μ to ε via γ4)?
Reasons for studying B-cells:
• What determines the quality of IgE antibodies?
• What is the role of Bregs in allergy/asthma?
• How could we target persistent plasma B-cells for IgE?
Immunotherapy: mechanism and monitoring
Many of the same questions need to be answered.
Blocking IgG4 antibodies?
What is the difference between IgE before and after therapy?
Th1 skewing?
Tregs?
Or perhaps Bregs?
Expression profiling / proteomics for biomarker search
Investigator-initiated trials needed. Companies are too small to
set up trials that include in depth immunological analyses. Better
insight in mechanism is a prerequisite for improvement of therapy.
Primary outcome (natural exposure) is an ill-controlled disaster!
Towards pollen chamber monitoring in season.