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responses to cross-reactive and non-cross-reactive epitopes on the allergic
response and resistance to Ascaris needs to be evaluated empirically.
ASCARIASIS INFLUENCING THE DIAGNOSIS
OF ALLERGY
High total IgE levels are strongly associated with asthma; 126,127 and this
biological marker has been used to assess the allergy component in
asthma diagnosis, even though a causal effect has not been demonstrated
and there are other conditions associated with elevated total IgE. In
tropical regions, where helminthiases are still public health problems and
are frequent inducers of high serum total IgE, 128 this test is not useful for
diagnosing asthma or other allergic diseases in individual subjects.
Probably because of its unspecific nature, 129,130 total IgE is being replaced
by specific IgE to allergens as a good marker of both atopy and allergic
diseases. But in the tropics there is an additional problem: the impact of
cross-reactivity in the diagnosis of mite allergy, the most important risk
factor for asthma. Ascaris cross-reactive allergens, such as tropomyosin
and GST, may influence mite allergy diagnosis when using the whole mite
extracts, as is routinely done in vitro and for skin testing. Therefore, in the
tropics the use of complete mite extracts for diagnosis could lead to false
positive results. Component-resolved diagnosis, including mite and
Ascaris purified allergens, could help to resolve this problem.
Another limitation of serologic allergy diagnostics in patients with asca-
riasis and other helminthiases is the presence of the carbohydrate epitope
galactose-
-Gal), expressed in nonprimate mammalian
proteins, suchas the cat allergenFel d5 (cat IgA). It has been reported that the
serologic diagnosis of cat allergy may be impaired among parasited
patients. 131 However, since patients of this study had several helminthiases,
it is difficult to define the particular importance in Ascaris -infected subjects.
There are other reports suggesting that intestinal helminths have
a
1,3-galactose (
a
-Gal, 132
but immunochemical studies on Ascaris extract show that deglycosilation
treatment does not significantly affect the specific IgE antibody binding to
the extract. 84 Further research is needed to confirmthe presence of this cross-
reactive carbohydrate in Ascaris .
It has been reported that skin test reactivity to clinically relevant
allergens is low among children with chronic severe helminthiases,
including ascariasis, 65 though the IgE response to allergens can be
demonstrated in those patients using serological methods. Several
mechanisms, among them the effects of total unspecific IgE competing
with specific IgE for FcER1 binding, and the anti-inflammatory action of
cytokines, mainly IL-10, may underlie this phenomenon. Also, parasite-
derived immunomodulators, such as ES-62 from filarial nematodes,
a
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