Revisiting the identification and cDNA cloning of T cell-replacing factor/interleukin-5

This is a perspective based on the paper "Cloning of complementary DNA encoding T cell-replacing factor and identity with B cell growth factor II," by Kinashi et al. (1). We have been interested in understanding the molecular basis of T-B cell cooperation for antibody formation. Although many investigators had described a number of different soluble factors that appeared to have biological relevance to T-B cell interactions, molecular basis of such active substances remained unknown for a long period of time. In this perspective, I will briefly summarize the history of the initial discovery of T cell-replacing factor/B cell growth factor II that appeared to be involved in B cell growth and differentiation, and outline the discovery and characterization of interleukin-5. Studies of interleukin-5 have provided strong evidence that a single cytokine exerts a variety of activities on diverse target cells.