In the pathogenesis of sparganosis, proteases have been considered to play important roles in tissue migration and parasite feeding. Several bands of proteolysis were observed when crude extracts of Spirometra mansoni plerocercoid (sparganum) were examined using gelatin substrate gel at neutral pH, of which two proteases of 198 and 104 kDa were purified by two chromatographic steps, and a 36 kDa protease was purified by gelatin-affinity and DEAE–anion exchange chromatography. All the purified proteases exhibited optimal activity at pH 7·5 and 0·1 M Tris–HCI. Proteolytic activities at 198 and 104 kDa were inhibited specifically by serine protease inhibitors, and 4-(amidinophenyl)methansulfonyl fluoride (APMSF, 0·5 m) and N-α–p–tosyl-L-lysine chloromethyl ketone (TLCK, 1 mM), which strongly suggested that these two proteases were trypsin-like proteases. The activity of the 36 kDa protease was inhibited by N-tosyl-l-phenylalanine chloromethyl ketone (TPCK, I mM) and chymostatin (0·1 mM), and was potentiated in 10 mM Ca2+ which showed that the protease had a chymotrypsin-like property. All the proteases were Schiff(PAS) positive. Proteases of 198 and 104 kDa degraded collagen completely within 24 h. The 36 kDa enzyme cleaved human recombinant interferon-γ (rIFNγ) and bovine myelin basic protein. In addition, all the purified proteins elicited strong antibody responses in the infected patients.

Evidence for the presence of adipokinetic hormone/hypertrehalosaemic hormone (AKH/HrTH)-like peptides in the parasitic nematodes Ascaridia galli and Ascaris suum has been obtained using insect bioassays which measure hyperglycaemic responses to peptides belonging to the AKH/HrTH family of insect hormones. A peptide fraction extracted from heads and tails of Ascaridia galli evoked a dose-dependent hyperglycaemic response when injected into the cockroach, Periplaneta americana. Maximal bioactivity was obtained with material that was equivalent to 38 mg (wet weight) of nematode. Bioactivity appeared to be highest in extracts from heads and tails of both male and female worms and could be fractionated into at least three peaks of hyperglycaemic activity by reversed-phase high-performance liquid chromatography. An extract from heads and tails of A. suum also evoked a hyperglycaemic response when injected into the cockroach, Blaberus discoidalis. The bioactivity was inactivated on incubation with pure endopeptidase 24.11, confirming the peptidic nature of the bioactive material. These results provide evidence for the existence of peptides related to the insect AKH/HrTH family of peptides in parasitic nematodes.

In the article ‘Necator americanus in inbred mice: a re-evaluation of primary infection kinetics’ published in Parasitology.