Biology Reference
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Cameroon were divided into those who persistently presented with no or
few worms, and those persistently presenting with high-level infections,
and screened for antibody responses to a crude mixture of antigens of
Ascaris, no good correlations could be found for either IgG or IgE antibody
responses with either phenotype. 28,29 But when only those that responded
to ABA-1 were taken, then a relationship did emerge between higher IgE
antibody responses to the protein and relative resistance to the infection
( Figure 3.2 ). This remains only an association, though there are reports
that immune responses to ABA-1-like proteins in other species of nema-
tode parasites may be protective. 30 A now widely-accepted interpretation
of this would be that T helper type 2 (Th2)-mediated inflammatory
responses (e.g. IgE, eosinophil, and/or mast cell-mediated) are operative
in ascariasis. 29,31,32 The Nigerian study also found that elevated levels of
serum proteins associated with inflammatory responses correlated with
natural resistance. 28 It could therefore be that the protective mechanism
involves direct attack by IgE and eosinophils, and/or local allergic
Low
Putative immune
Category 1
High
Intermediate
Category 2
Highly susceptible
Category 3
0
25
50
75
100
Percent of subjects
FIGURE 3.2 Association between relative resistance to Ascaris lumbricoides infection
and IgE antibody against ABA-1. Infected patients (ages 5
15 years) in Nigeria were
categorized as positive for IgG antibody to ABA-1 by radioimmunoassay and then sub-
divided into those responding with high, intermediate or low levels of IgE antibody to the
recombinant form of the protein produced by A. lumbricoides. The proportion of individuals
with the higher levels of IgE antibody to ABA-1 within the three infection classes showed
pronounced differences (66.7% in category 1, 37.5% in category 2, and only 10% in category
3), with more individuals in the putatively immune group having higher levels. For full
details including statistical analysis see. 28 A similar effect was observed in a study carried
out in Cameroon. 29 Figure taken from 28 with permission.
e
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