Recent epidemiological data suggest that the allergic manifestations in
industrialised countries have increased enormously in the last years,
with
a percentage between 20 and 30% of the population. Among the allergenic
causes, pollens are one of the main responsible factors. The most
allergenic species belong to important families such as: fagacee,
urticacee, oliacee, composite and graminacee. The Parietaria belongs to
the Urticaceae family and is considered to be the most common group of
allergenic plants in the Mediterranean area. The genus includes: P
judaica (Pj), P. officinalis, P. lusitanica, and P. cretica e P.
mauritanica. In Italy, P. officinalis is largely common in the Central-northern regions, meanwhile the P. judaica is spread all over the national
territory and on the coast. DNA recombinant technology has been used to
isolate and characterize the Parietaria judaica allergens. Thanks to this
strategy, we have been able to isolate two major allergens, called Par j1
and Par j2 and some other isoforms.
The Parj1 is a protein of 139 aa and a molecular weight of 14.726 Da; it
is a major allergen because it reacts with 95% of the sera from Pj
allergic patients. The Par j2 allergen consists of 102 aa and a molecular
weight of 11344 Da. It shows a homology of 45% at amminoacid level with
the Parj1 and reacts with the 82% of the sera of allergic subjects.
Furthermore, an experiment of cross-inhibition with increasing amount of
rParj2 and rParj1 has shown that the two molecules have a different IgE
repertoire. In addition, when a pool of sera from Pj allergic patients is
pre-incubated with a large excess of the rParj1 and rParj2, the IgE
binding activity towards the Pj pollen is almost inhibited suggesting
that
those two allergens are the most important actors of this allergic
reaction. Homology search at the EMBL s data bank has shown that the Par
j1 and the Parj 2 belong to a family of proteins known as non specific
lipid transfer protein (LTP). These proteins consist of a alpha-alpha-alpha-alpha-beta conserved secondary structure containing 8 cysteine
residues to form four disulphide bridges compacting the four alpha
helices. The Par j 1 and Parj2 allergens present all the characteristics
of the ns-LTP, and it has been possible to determine the structural model
of the molecules by homology. While the allergy symptoms can be cured
pharmacologically, the only preventive therapy is the specific
immunotherapy (SIT). However, most of the crude extracts used in commerce
are a mixture of many components difficult to standardize. This strategy
might lead to the injection of allergenic components to which the patient
is not sensitive causing new sensitations. In addition, the injection of
the wild type allergen presents the possibility of dangerous side effects.
A large body of evidence has clearly shown that recombinant allergens
present an immunological behaviour similar to their native counterpart
when analysed by Western blot, Skin Prick Test and Histamine release
assay. For these reasons, the use of recombinant allergens (RA) may
represent an improvement for the:
a)diagnosis of the allergic disease,
b)to monitore the antibody production during the specific immunotherapy;
c)to design hypoallergenic derivatives of the wild type allergen to use in novel therapeutic approaches.
Focus