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possible that such a “sticky finger” could also be involved in its interac-
tion with other proteins.
nemFABPs probably have functions in nematodes beyond merely
being exported from the cell to transport lipids. It is clearly tempting to
suppose that the existence of the loop at the opposite side of the molecule
from the portal pertains to a previously unknown function of nemFABPs,
and that As-p18 and other nemFABPs are present in perivitelline fluid of
the egg (though seemingly also present elsewhere 90 ) to perform an
important role in nematode reproduction. That may be of more than
general interest given that it is the reproductive stages of many nematode
infections that cause the major part of associated pathologies (as in
onchocerciasis). It would be interesting to know whether inactivation or
deletion of nemFABP genes produce abnormal or reproduction-disabled
phenotypes, C. elegans being the obvious system within which to test
the idea.
CONCLUDING REMARKS
This chapter concentrated on proteins produced by both species of
Ascaris, and how immune responses to them, and direct structural anal-
ysis of the proteins themselves, have illuminated principles that apply
both to ascariasis and other nematodiases. The concentration on proteins
is partly because they are the easiest products to investigate in relation to
biochemistry, immune responses, and immunogenetics. But other types of
molecule may be important in immunological phenomena, such as the
modulation of responses by T cells, B cells, and other immune-associated
cells that have been found with crude preparations from the worms, the
active principles of which remain to be identified. 104 e 108 Compounds
such as glycolipids and other entities could trigger specific toll-like
receptors and other innate responses because their chemistries are of
types that do not occur in mammals, so could therefore act as generic
signals. Equally, it is clear from examples, such as ABA-1 and other NPAs,
that nematodes produce proteins of types unique to them, the structures
of which could also act as generic signals of nematode infection. 107 Given
that NPAs are binding proteins for a range of hydrophobic ligands, some
of which may be unique to nematodes, then they may yet provide
important clues. It is conceivable that NPAs are not allergenic by dint of
their amino acid sequences or overall tertiary structure, but only in
association with the lipid ligands that accompany them. For the moment,
we have good information on the ligand binding propensities of NPAs
arising from simple binding assays using lipids that are of known rele-
vance to mammalian physiology and immune signaling, but not what
compounds the parasites themselves actually use them to transport.
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