CTLA4 and infection: Conversely, in a study considering the effect of re-infection following unisexual infection (18), we were able to show that an 11-week unisexual pre-infection with female schistosomes suppresses the Th2 response upon subsequent re-infection with bisexual schistosomes and upregulates the expression of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4).