Biology Reference
In-Depth Information
in industrialized countries
11
e
14
and also urbanizing populations in non-
industrialized countries.
This chapter will review what is known of the immune response to
Ascaris in pigs and humans and how infections may modify the immune
and inflammatory response of the host. We will also discuss the potential
clinical effects of this immune modulation.
IMMUNOLOGY OF ASCARIASIS
Immunology of
in Pigs
Great progress has been made over the past 20 years in our under-
standing of the immune response to A. suum in pigs. Earlier studies
showed that the inoculation of pigs with infective eggs was associated
with the development of specific systemic IgG1, IgA, and IgM antibody
responses,
5,15
but that the predominant antibody secreting cells (ASC) in
the mucosa of the proximal jejunum,
5
duodenum,
16
and bronchi
16
were of
the IgA isotype.
5
That the immune response to A. suum in the pig is
predominantly Th2 is reflected by an elevated peripheral blood eosino-
philia,
17,18
elevated frequencies of parasite-specific monocytes secreting
IL-4 in peripheral blood and intestinal lymph nodes,
18
and the increased
expression of IL-4 in plasma and Th2 cytokines (e.g. IL-4 and IL-13) in the
intestine
19,20
and liver.
21
An increased expression of IL-10 has been
observed in the intestine and other tissues during infection
19
where it may
have a role in the regulation of inflammation.
22
Resistance toA. suum inpigs has beenobserved followingmultiple oral
infections with A. suum eggs,
17,23,24
with radiation-attenuated A. suum
eggs,
25,26
and following immunization with parasite-derived products.
27
Partial protection has also been achieved by giving colostrum from
immunized sows
28
and by passive transfer of hyperimmune sera.
28
Protective immunity toA. suum in swinemay occur in the liver, lungs, and
in the intestine. Different infection or immunization strategies may have
stronger effects on immunity generated in a particular tissue. A strong
liver white-spot reaction, reflecting the host inflammatory response to the
presence of the larvae in the liver, is a typical consequence of a secon-
dary challenge exposure to infective eggs,
29
Ascaris suum
although this reaction
diminishes over time with trickle infections.
24
Chronic natural and multiple inoculations with eggs has been associ-
ated with the development of pre-hepatic intestinal immunity
29,30
while
immunization with irradiated eggs or with A. suum antigens
27,31
is
associatedwith post-hepatic protective immunity. Relatively little is known
of the specific immunological mechanisms bywhich protection is achieved.
The intestinal expulsion of larvae that have migrated through the lungs has
