IL9 and infection: It was also observed that treatment of BALB/c mice with a neutralizing antibody against IL-4, a key mediator of the TH2 type, could suppress IL-9 synthesis and a correlation of IL-9 production with the proliferation of antigen specific TH2 cells in BALB/c mice that were detected after four weeks of infection, suggesting its association with a TH2 phenotype [35].