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humans and infected animals Ascaris brings sensitization and IgE-
mediated asthma, including immediate-type cutaneous reactivity and
airway responses after aerosol challenge with parasite extract. 59,60,62,63,70
For example, Hagel et al. found that specific IgE levels to Ascaris and
positivity of skin test with the nematode extract were associated with
bronchial hyper-reactivity in children from a rural area of Venezuela.
Also, the percentage of forced expiratory volume in 1 second (FEV1)
predictive values correlated inversely with anti- Ascaris IgE levels. In
contrast, in urban children the same associations were with specific IgE to
Dermatophagoides pteronyssinus . 70
It has therefore been proposed that the systemic enhancement of the
Th2 response during helminth infection induces an allergic polarization
to bystander antigens, such as aeroallergens. 61,94,95 There is some exper-
imental evidence supporting this contention. Earlier studies described
that antigens of A. suum potentiate IgE response to ovalbumin in guinea-
pigs. 96,97 Also, Ascaris pseudocelomic body fluid and the purified allergen
ABA-1 prolonged the response to ovoalbumin as third-party allergen but
they did not enhance the IgE levels to OVA. 98 In another investigation,
co-administration of hen egg lysozyme with the excretory/secretory
products of Nippostrongylus brasiliensis results in generation of egg
lysozyme-specific lymphocyte proliferation, IL-4 release, and IgG 1 anti-
body responses, supporting the role of some nematode products as
adjuvants for third-party antigens. 99 Furthermore, it has been shown that
unidentified components in the body fluid of Ascaris promote a Th2
response and are adjuvants for specific IgE synthesis to some parasitic
allergens like ABA-1. 100 Since, in addition to this allergen, Ascaris extract
has at least 11 human-IgE binding components, the potentiating effect
may be more generalized, 84 and because of co-exposure, this could
happen for cross-reactive and non-cross-reactive mite allergens.
Based on their findings from early epidemiological studies, Lynch
et al. 82 suggested that the prevalence of allergies may be lower in indi-
viduals with high parasite burdens of geohelminths compared to those
with low burdens. This idea is now widely accepted and has been related
to the acute and chronic clinical phenotypes observed in helminth-infected
humans. 101 In addition, intermittent universal de-worming programs in
pre-school and school-aged children reduce parasite burdens and boost
the immune response to the soil-transmitted helminthes, because rein-
fections may elicit immune responses different in nature from the original
primary infections. Therefore, it is theoretically possible that, in the pres-
ence of intermittent infections with lowworm burdens, exposure to Ascaris
promotes allergic sensitization and asthmatic symptoms by increasing the
synthesis of parasite-specific, mite-specific, and mite e parasite
cross-reacting IgE antibodies. The clinical impact may be particularly
important in urban zones of underdeveloped countries, because in rural
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