We investigated additional cytokine signals involved in residual eosinophilia in the absence IL-4Rα signaling and defined that IL-4Rα−/−/IL-5−/− double-knockout mice displayed significant eosinophil deficiency compared with IL-4Rα−/− mice and were susceptible to chronic fecund adult filarial infections. Here, IL5 is linked to Increased total eosinophil count.