Diagnostic markers of clinical allergy versus sensitisation to peanut

Peanut allergy (PA) is particularly problematic since it is increasingly common in infants and
children, may be life-threatening, frequently persists through adulthood and has a significant impact
on children?s quality of life.
The diagnosis of PA is based on a combination of a history of allergic reaction(s) to peanut and
positive allergy tests. However, this is not reliable because many patients have positive allergy tests
and tolerate peanut whilst others have positive allergy tests and are peanut allergic. The only way to
clarify this is by giving the child peanuts in oral food challenges (OFC). However, OFC are expensive,
laborious and potentially dangerous, as they may induce allergic reactions.
Our proposed research project aims to provide fundamental insights into the mechanisms of
allergy and tolerance and also to distinguish between peanut allergic children and those who have
positive allergy tests but tolerate peanut without the need for OFC.
This project will improve allergy diagnosis, allowing for a more accurate distinction of allergic
children among children with positive allergy tests, not only to peanut but also to other allergens. By
understanding why some children with positive allergy tests react and others do not, we may
develop new definitive treatments for PA

Background: In the United Kingdom, 2% of primary school children will develop peanut allergy but
10% will develop serum specific IgE to peanut. This poses diagnostic difficulties and dangerous oral
food challenges(OFC) are required. Why is it that some patients have high serum specific IgE levels
to peanut and tolerate it and others have low specific IgE levels and react violently?
Hypotheses:
Two separate hypotheses will be addressed:
1. Peanut specific IgE is functionally different in allergic and tolerant children;
2. The functionality of peanut specific IgE is similar and sensitized but tolerant children have an
inhibitor that blocks IgE function.
Objectives:
1) To understand the immunological differences that underpin sensitization and allergy;
2) To improve the diagnosis of peanut allergy while reducing the need for OFC.
Study design:
Four groups of children will be compared:
- Peanut allergic(PA) ? peanut IgE positive and peanut allergic(n=25);
- Peanut sensitized(PS) ? peanut IgE positive, never reacted to peanut and eat peanut(n=25);
- Peanut allergy resolved(PR) ? peanut IgE positive and have outgrown peanut allergy(n=25);
- Non-allergic(NA) ? peanut IgE negative and eat peanut(n=25).
PA, PS and PR groups will be matched for serum peanut specific IgE levels.
Methodology:
To test the first hypothesis, we will:
- perform basophil mediator release assays(histamine, IL-4 and IL-13), following pre-incubation
with sera and subsequent stimulation with peanut extract;
- purify IgE from sensitised but tolerant children(PS and PR) and assess whether it induces
basophil histamine release;
- analyse peanut specific IgE for specificity and clonality(peanut peptide and epitope recognition
of IgE, using ImmunoCAPTM and microarray immunoassays) and for affinity and avidity(using
surface plasmon resonance).
To test the second hypothesis, we will:
- pool sera from sensitised but tolerant with sera from allergic children and assess whether
basophil mediator release is inhibited;
- purify antibody isotypes other than IgE(e.g IgG4) from sensitised but tolerant children and
assess whether basophil mediator release is inhibited;
- assess basophil intracellular signalling protein activities, excitatory(Syk and p38-MAPK) and
inhibitory(SHIP), on western blotting, in case an inhibition is observed.
Scientific and medical opportunities:
This study will extend our knowledge about the mechanisms that determine clinical reactivity to
peanut in sensitized patients and define superior diagnostic markers for peanut allergy. The results
may be extended to other food and respiratory allergens. By understanding why some IgE react and
other do not, we may target therapeutical strategies to induce tolerance and provide definitive
treatment for allergy.