Use of PZQ will increase in the foreseeable future, whether given alone or coadministered with other anthelminthics in integrated control programmes. PZQ resistance remains a threat and its prevention requires adequate monitoring of current mass drug administration programmes and development of new schistosomicides.

Soluble egg antigens of the parasitic helminth Schistosoma mansoni (S. mansoni egg antigen [SEA]) induce strong Th2 responses both in vitro and in vivo. However, the specific molecules that prime the development of Th2 responses have not been identified. We report that omega-1, a glycoprotein which is secreted from S. mansoni eggs and present in SEA, is capable of conditioning human monocyte-derived dendritic cells in vitro to drive T helper 2 (Th2) polarization with similar characteristics as whole SEA. Furthermore, using IL-4 dual reporter mice, we show that both natural and recombinant omega-1 alone are sufficient to generate Th2 responses in vivo, even in the absence of IL-4R signaling. Finally, omega-1–depleted SEA displays an impaired capacity for Th2 priming in vitro, but not in vivo, suggesting the existence of additional factors within SEA that can compensate for the omega-1–mediated effects. Collectively, we identify omega-1, a single component of SEA, as a potent inducer of Th2 responses.

Schistosoma mansoni infections in mice were treated with subcurative multiple doses of either praziquantel (PZQ) or oxamniquine (OX). With an early exception, the drug treatments commenced when the worms were adult, but before the infections had become fully patent, and the eggs subsequently produced by worms that had survived the drug treatments were used to infect snails. Six or seven drug-treated passages of S. mansoni in mice were completed for each of the drugs, with the amount of drug administered to the infected mice generally being increased with each passage. Eighty percent of the worms of the sixth passage selected for PZQ resistance survived three doses of 300 mg/kg of PZQ given between days 28 and 37 after infection, and 93% of those of the seventh passage survived the same drug dose. In contrast, only 13% of worms of the sixth PZQ-selected passage survived three doses of 200mg/kg of OX given during the same period after infection. Only 11% or fewer worms derived from S. mansoni infections that had not been subjected to any drug pressure survived the 3 x 300 mg/kg PZQ treatments. Worms selected for OX resistance over six passages were completely resistant to three doses of 200 mg/kg, but only 26% survived three doses of 300 mg/kg of PZQ. Therefore, the results indicate that S. mansoni subjected to drug pressure may develop resistance to schistosomicidal drugs over the course of relatively few passages, but that cross-resistance between PZQ and OX does not occur. This is the first demonstration of drug resistance to PZQ, the current drug of choice for human schistosomiasis.

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