The switch from Th1 to Th2 is crucial for survival of the host, indicated by the findings that patients with severe hepatosplenic schistosomiasis have high levels of Th1-associated cytokines [Tumor necrosis factor α (TNFα), IFNγ], while asymptomatic patients exhibit high levels of Th2 associated cytokines (IL-4, IL-5, IL-13) and IgE (23). This evidence concerns the gene TNF and schistosomiasis.