Brugia malayi and Ancylostoma ceylanicum express homologues of the mammalian cytokine macrophage migration inhibitory factor (MIF) [95], and in a Th2 environment, such as that activated by helminth infection, Brugia MIF synergises with IL-4 to induce the development of regulatory M2 macrophages [96]. The gene discussed is MIF; the disease is helminthiasis.