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 an
ti-murine IL-5-neutralizing polyclonal antibody. When bone marrow cells fro
m normal rats were incubated with recombinant rat IL-5 in medium containing
methylcellulose, the colony formation by eosinophilic cells was induced. F
urthermore, when rat peritoneal eosinophils were incubated with recombinant
rat IL-5, the spontaneous decrease in eosinophil viability was inhibited i
n a time- and concentration-dependent manner. In addition, the recombinant
rat IL-5-induced eosinophil survival was inhibited by an anti-murine IL-5-n
eutralizing polyclonal antibody. These findings suggest that rat IL-5 acts
as B cell growth factor II, eosinophil differentiation factor, and eosinoph
il survival-enhancing factor.