We also demonstrated that a schistosome cysteine protease, S. mansoni cathepsin B1 (SmCB1), which is secreted from the gut of the parasite, was a principal target of the IgE response [21], suggesting this worm-secreted antigen may contribute significantly to TH2 polarization of the nascent CD4+ T cell response during early infection. This evidence concerns the gene CTSB and infection.