The macrofilaricidal efficacy of both OXF and FBZ was reduced in all tested immunodeficient strains, and treatment efficacy was lowest in strains with more severe immunodeficiency, i.e., IL-4r/IL-5−/− vs. ΔdblGata1 mice, or completely abrogated in Rag2/IL-2rγ−/− mice. The gene discussed is IL4R; the disease is immune system disorder.