Biology Reference
In-Depth Information
in effector cells, both
in vivo
and
in vitro
. ABA-1, although present in
other nematodes, is not cross-reactive with any of the
B. tropicalis
or
D. pteronyssinus
allergens, which means that
it can be useful
for
component-resolved diagnosis of allergic diseases in the tropics.
Possible Effects of Ascaris Allergens on the Clinical Evolution
of Asthma
One potential mechanism to enhance the IgE responses to allergens in
asthmatic patients living in the tropics is cross-reactivity (reviewed in
111
).
It can act at several stages of ascariasis or asthma, and the tropical envi-
ronment provides appropriate conditions for this relationship.
First, there is the possibility of early life co-exposure to allergens from
mites and
Ascaris
. The complex interactions elicited by allergenic mole-
cules from different sources acting together on the innate and adaptive
immune responses are not yet clearly defined, but one possible outcome is
the enhancement of the allergic responses.
47
Early IgE responses to mites
and
Ascaris
have been observed in children from tropical regions and
some studies have found clinical relevance.
70,112
Second, parasited children receive anthelminthic therapy during
intermittent universal de-worming programs aimed at pre-school and
school age. Since the socioeconomic causes of the infections are not
eliminated, children become reinfected several times and modified
secondary immune responses may boost IgE reactivity against cross-
reactive allergens from other sources (e.g. mites). Repeated anthelmintic
treatments significantly increase the production of Th2 cytokines, IL-5,
and IL-13 and decrease the production of IL-10 by peripheral blood
leukocytes after stimulation with
Ascaris
antigens, although no changes
were observed when stimulating with
D. pteronyssinus
and cockroach
113
;
it has also been found that long-term periodic treatments in a community
with various helminthiases,
including ascariasis,
is associated with
increase of allergen skin reactivity.
114
In schistosomiasis, there is evidence that anthelminthic treatment
influences the evolution of several mechanisms of immunity, including
increasing the proportion of effector T cells and the switch to protective
antibody isotypes such as IgE,
115,116
probably because of higher loads of
antigens from dead parasites,
115,117
and the removal of immunosuppres-
sive parasite products.
118
Reinfections can stimulate memory cells,
119
and
the mentioned effects of anthelmintics may be also present during the
treatment of other helminthiases such as ascariasis.
Third, as it is well known, mite-allergens exposure is perennial and
very intense in the tropics; therefore, in the
Ascaris
-infected population
(current or past) susceptible to asthma, this may be another cause of
increasing IgE responses to cross-reactive allergens. It can be speculated
