Antigenic cross-reactivity between Necator americanus and Ascaris lumbricoides in a community in Papua New Guinea infected predominantly with hookworm.

Sero-epidemiological data are presented in which antigenic cross-reactivity between Necator americanus and Ascaris lumbricoides has been investigated in a community in Papua New Guinea infected predominantly with N. americanus. It is our contention that the antigenic cross-reactivity which undoubtedly exists between these species accounted for (i) a peak in antibody levels against N. americanus in 10-13 years old children (driven by infection with A. lumbricoides), and (ii) the maintenance of apparent antibody levels against A. lumbricoides in older age groups (driven by infection with N. americanus in the absence of overt infection with A. lumbricoides). Cross-reactivity was analysed further, and apparently N. americanus-specific epitopes identified, by immunoblotting. These observations could have considerable bearing on the interpretation of data from sero-epidemiological studies which failed to take account of concurrent infection with these parasites.

Necator americanus secretory acetylcholinesterase and its purification from excretory-secretory products by affinity chromatography.

Acetylcholinesterase (AChE) secretion by adult N. americanus was enhanced in vitro by incorporating insoluble collagen rafts into culture dishes. Enzyme produced in this way had preferential substrate specificity for acetylthiocholine iodide (ATC), and its activity was inhibited by eserine (1.1 x 10(-8) M). Ancylostoma ceylanicum, another hookworm species, failed to produce comparable amounts of AChE in culture. AChE was efficiently purified from culture medium by affinity chromatography on edrophonium sepharose; 81% of the AChE activity was retained by the affinity matrix, although this fraction contained only 4.3% of the protein loaded. Antisera raised against purified AChE in rabbits immunohistochemically stained the oesophageal glands of the parasite, and reacted with molecules of 32, 60, 80, 140 and 220 kDa in reduced adult ES products on Western blotting, although differential activity was observed against worm homogenates and earlier developmental stages. On IEF, purified AChE resolved predominantly with a pl of 3.55; proteins with a similar pl were recognized by rabbit anti-AChE. IgG preparations of this antiserum inhibited AChE activity in ES products, and inhibited AChE secretion by adult worms in culture. The availability of this immunological probe will allow definitive experiments to be conducted on the role of this enigmatic enzyme in the host-parasite relationship.