Biology Reference
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the GI tract. Immunoregulatory cytokines IL-10 and transforming growth
factor (TGF)- b can be measured systemically in Ascaris-infected individ-
uals 18,19 although the particular cellular source(s) of these cytokines has
not been fully characterized. Ascaris body extracts contain several
potent immunosuppressive antigens, some of which are decorated with
phosphorylcholine, a well-characterized inducer of immunosuppres-
sive immune responses. 20 It has been demonstrated by Silva et al. 21 that the
function of antigen presenting cells (such as dendritic cells) exposed to
Ascaris antigens is suppressed in an IL-10-dependentmanner. The protein
fromAscaris suum (PAS-1) has been shown to have the ability to suppress
the immune response to an unrelated protein in mice, a phenomenon
that was associated with increases in IL-10 production 22 demonstrating
the potential strength and systemic nature of this response. However, IL-
10 production may not be strictly necessary to mediate this effect.
Mucosal inflammatory immune responses stemming from induced
allergy in mice was suppressed by administration of Ascaris suum body
extracts in an IL-10 independent manner suggesting that other factors
such as TGF-
can mediate this effect. 23 This immunoregulatory immune
responsemay help to facilitate the longevity of Ascaris adult nematodes in
the intestine.
After hatching, Ascaris larvae undergo migratory phases from the GI
tract through the liver and lungs before being re-swallowed and estab-
lishing infection in the GI tract as adult nematodes. Not much is known
regarding the immune responses generated by migrating Ascaris larvae in
humans, but porcine models of ascariasis using A. suum infection suggest
that migration is accompanied by an inflammatory immune response in
the liver and lungs (see also Chapters 1 and 14). In the porcine liver this
response manifests itself as “white spots” of cellular infiltrates, similar to
granulomatous lesions, which are initially composed of eosinophils and
neutrophils with the subsequent infiltration of macrophages, T and B
cells, and fibroblasts. 24,25 Larval debris can also be found in mature white
spots and white spot formation is associated with resistance to the
establishment of A. suum infection in pigs. 26
White spot formation has also been observed in the lungs, and the
most prominent syndrome caused by larvae migrating through the
lungs is a respiratory syndrome known as Loeffler's syndrome. This
syndrome results in eosinophilic pneumonia whereby the eosinophil
granule release alters the normal air spaces leading to breathing diffi-
culties. 27 Eosinophil responses are hallmarks of Th2 responses, in
particular IL-5 production, 28 suggesting that larval migration can be
a strong inducer of Th2 responses and white spots are the result of type 2
inflammatory immune responses. Th2 responses may be induced by
innate lymphoid cells, a recently described immune cell type that is
thought to maintain epithelial barriers, such as those found in the lungs
b
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