The interleukin-4-inducing principle from Schistosoma mansoni eggs (IPSE/alpha-1) is a major immunogenic component of schistosomes. It potently triggers the release of interleukin-4 from basophilic granulocytes in an IgE-dependent manner, suggesting a key function in the modulation of the host’s immune response to Schistosoma mansoni infection. Here we present the near complete assignment of an IPSE/alpha-1 variant, IPSEDNLS, which comprises the core domain of the protein.