In contrast, extracellular infections with metazoan parasites, such as nematodes and trematodes, can trigger a cell-mediated T helper 2 (Th2)-type immune response [13,14], which favours the secretion of interleukin 4 (IL-4), interleukin 6 and interleukin 13 cytokines that, in turn, mediate the recruitment of eosinophils, mast cells and basophils. The gene discussed is IL4; the disease is infection.