 Furthermore, non-cytotoxic innate lymphoid cells (ILC) as well as mucosal epithelial cells, macrophages and B cells secrete IFN-γ.The presence of IFN-γ in T helper cells makes that undifferentiated CD4+ cells (Th0 cells) to differentiated into Th1 cells.Therefore, there is a positive feedback loop which suppress Th2 cell differentiation.