Immunomodulation in helminth infections shows two common modes of action [154]: (i) certain groups of proteins play key roles in bringing about changes in the host immune response; and (ii) T regulatory (Treg) cells and the induction of IL-10 play central roles in helminth-induced host immune modulation, by means of classical Foxp3+ CD4 cells or IL-10-secreting populations of CD4+ or CD8+ cells. The gene discussed is FOXP3; the disease is helminthiasis.