Analysis of Biological Activities of Recombinant Rat Interleukin-5

We analyzed the biological activities of recombinant rat interleukin-5 (IL-5). Purified recombinant rat IL-5 promoted the proliferation of T88-M cells in a concentration-dependent manner, and its effect was inhibited by an anti-murine IL-5-neutralizing polyclonal antibody. When bone marrow cells from normal rats were incubated with recombinant rat IL-5 in medium containing methylcellulose, the colony formation by eosinophilic cells was induced. Furthermore, when rat peritoneal eosinophils were incubated with recombinant rat IL-5, the spontaneous decrease in eosinophil viability was inhibited in a time- and concentration-dependent manner. In addition, the recombinant rat IL-5-induced eosinophil survival was inhibited by an anti-murine IL-5-neutralizing polyclonal antibody. These findings suggest that rat IL-5 acts as B cell growth factor II, eosinophil differentiation factor, and eosinophil survival-enhancing factor.