Biology Reference
In-Depth Information
phenotypes is increasing,
85
e
87
probably because the surveys have been
expanded to include urban zones where parasitism is less endemic but
still present.
CAN HELMINTH INFECTIONS INCREASE
THE ALLERGIC RESPONSE?
In addition to the downregulation of allergic responses detected during
some nematode infections (more evident and better studied in schisto-
somiasis
88
), a strong IgE response dominates in human
Ascaris
infections,
a phenotype that, for a long time, has been interpreted as potentially pro-
allergenic and probably related to the complex life-cycle and the antigenic
composition of this nematode. Also, high total IgE levels are typical of
helminthiases, which seem to be the result of polyclonal B cell stimulation
by parasite products.
89,90
Table 2.1
shows a list of issues supporting the
hypothesis that, in some conditions, ascariasis enhances IgE responses to
environmental allergens and allergies.
After penetration of the intestinal mucosa,
Ascaris
larvae migrate to the
liver, inducing the formation of granulomas, extensive inflammation, and
tissue injury.
91
Surviving larvae reach the lungs and generate an inflam-
matory infiltrate in the airways dominated by severe peri-alveolar
eosinophilia.
92,93
Larvae induce antibody production; high levels of
polyclonal and specific IgE are a hallmark of the infection and, in humans
and pigs, immunity includes the generation of parasite-specific IgE
antibodies against larvae and adult worms.
30,31
Experiments show that in
TABLE 2.1 Experimental and epidemiological findings supporting that ascariasis may
enhance the IgE response
Findings
References
Natural infection is associated with a polarized Th2 cytokine
response and high levels of total and anti-
Ascaris
IgE
61
,
70
,
89
,
95
,
171
,
177
e
181
In some individuals, natural infection induces IgE-mediated
allergic respiratory and cutaneous symptoms
59
,
182
,
183
In experimental human and other animal models, bronchial
challenges with
Ascaris
extract induce asthma symptoms
60
,
62
,
63
Experimental ascariasis in animals enhances IgE response to
bystander antigens
96
e
99
Several epidemiological surveys have found that ascariasis is
a risk factor for asthma and atopy
66
e
72
IgE responses to
Ascaris
allergens is more frequent and
stronger in mite-sensitized asthmatic patients
73
,
110
,
162
,
171
