Biology Reference
In-Depth Information
areas the infections are usually more intense and associated with higher
degrees of immunosuppression. Also, differences in mite fauna and levels
of mite-allergen exposure may influence the type of sensitization and, in
consequence, the relevance of cross-reactivity.
TH
E ALLERGENS OF A. LUMBRICOI
DES
As already mentioned, domestic mites are the most important risk
factor for asthma in the tropics and their allergens have been extensively
characterized. To study the effects of the immune responses to
Ascaris
on
allergy, molecules that induce allergy symptoms, those that generate
a protective IgE immune response, and those that promote both effects
should be identified. Some antigenic components of
Ascaris
(e.g. As14,
As16, As24, As37, PAS-1) have been analyzed,
102
e
106
but information
about the allergenic composition and its clinical impact in humans is still
very limited. Less is known about the influence of the IgE/IgG immune
responses to other nematode molecules, such as glycoproteins and
glycolipids
107,108
on the evolution of allergy. Also, the role of chitin as
adjuvant of the Th2 responses
109
is particularly interesting since it is an
important component of
Ascaris
cuticle and could partially explain the
prominent allergenic properties of this parasite. A systematic search of
antigen identification and allergens of
Ascaris
inducing immune
responses in humans is currently ongoing in our laboratory.
Asc s 1, also known as ABA-1, and Asc l 3,
Ascaris
tropomyosin, are the
officially accepted (WHO/IUIS) allergens of this nematode. In addition,
several IgE binding components have been detected using one-
dimensional (1D) and two-dimensional polyacrylamide-gel electropho-
reses (2D-PAGE). Among the 12 allergenic components we have found,
84
there are seven that are cross-reactive with mite allergens and five that are
Ascaris
specific. This explains the high degree of cross-reactivity between
mite and
Ascaris
extracts and supports the idea that ascariasis may lead to
an enhanced IgE response to several mite allergens. Tropomyosin and
glutathione-transferase (GST) are two of these cross-reactive allergens.
Recently, the immunochemical properties of
Ascaris
tropomyosin
(Asc l 3) were revealed. Very high allergenic cross-reactivity between the
natural Asc l 3 and
Blomia tropicalis
tropomyosin, Blo t 10, was found
using sera from asthmatic patients.
84
These results were confirmed using
a recombinant
Ascaris
tropomyosin expressed in a bacterial system.
110
IgE antibodies to rAsc l 3 represented a high proportion (~50%) of the
total IgE response to an unfractionated parasite extract and there was
allergenic equivalence between rAsc l 3 and the native counterpart in
the
Ascaris
extract. Moreover, anti-tropomyosin IgE antibodies from
sensitized subjects reacted against Asc l 3 and induced mediator release
