Cloning and characterization of profilin (Pru du 4), a cross-reactive almond (Prunus dulcis) allergen

The identity of allergenic almond proteins
is incomplete.
Objective: Our objective was to characterize patient IgE
reactivity to a recombinant and corresponding native
almond allergen.
Methods: An almond cDNA library was screened with sera
from patients with allergy for IgE binding proteins. Two
reactive clones were sequenced, and 1 was expressed. The
expressed recombinant allergen and its native counterpart
(purified from unprocessed almond flour) were assayed by
1-dimensional and 2-dimensional gel electrophoresis,
dot blot, and ELISA, and screened for cross-reactivity
with grass profilin.
Results: The 2 selected clones encoded profilin (designated Pru
du 4) sequences that differed by 2 silent mutations. By dot-blot
analyses, 6 of 18 patient sera (33%) reacted with the
recombinant Pru du 4 protein, and 8 of 18 (44%) reacted with
the native form. ELISA results were similar. Almond and
ryegrass profilins were mutually inhibitable. Two-dimensional
immunoblotting revealed the presence of more than 1 native
almond profilin isoform. The strength of reactivity of some
patients’ serum IgE differed markedly between assays and
between native and recombinant profilins.
Conclusion: Almond nut profilin is an IgE-binding food protein
that is cross-reactive with grass pollen profilin and is
susceptible to denaturation, resulting in variable reactivity
between assay types and between patients.
Clinical implications: Serum IgE of nearly half of the tested
patients with almond allergy reacts with almond nut profilin.
Because most patients also had pollinosis, the well-known crossreactivity
between pollen and food profilins could account for
this pattern of reactivity.