Concanavalin A-stimulated rat spleen cells produce a soluble factor that supports growth of the mouse IL-3-dependent cell line Ea3.123, but not three other IL-3-dependent lines.

Several cloned, non-leukaemic mouse haemopoietic cell lines are believed to be uniquely dependent on interleukin-3 (IL-3) for their survival. All of these lines require the addition of WEHI-3B cell-conditioned medium for their growth. We have examined the growth requirements of four IL-3-dependent cell lines and found that only one, Ea3.123, is able to grow in medium conditioned by concanavalin A-stimulated rat spleen cells (rat ConACM), whereas the other three, AC2, 32D cl-23 and FDC-P2, are not. Medium conditioned by the growth of concanavalin A-stimulated mouse spleen cells (mouse ConACM) supports the growth of all four cell lines. The Ea3.123-supporting activity in rat ConACM appears to be of smaller size (approximately 27,000) than the activity in mouse ConACM and WEHI-3BCM (approximately 38,000). The activity is unlikely to be due to GM-CSF, since post-endotoxin serum containing GM-CSF does not support growth of Ea3.123, nor is it likely to be IL-2, since we were able to remove IL-2 by absorption with CTLL-16 cells without affecting the ability of rat ConACM to support Ea3.123 cells. Our findings have important implications for the assay of IL-3, and mechanisms by which dependent cells respond to IL-3.