MAST-CELL GROWTH-ENHANCING ACTIVITY (MEA) IS STRUCTURALLY RELATED AND FUNCTIONALLY IDENTICAL TO THE NOVEL MOUSE T-CELL GROWTH FACTOR-P40 TCGFIII (INTERLEUKIN-9)

We have previously shown that certain bone marrow‐derived mast cell (BMMC) lines proliferate in response to a mast cell growth‐enhancing activity (MEA) that is distinct from interleukin (IL) 3 and IL 4. Here we provide evidence that MEA is identical with the recently cloned mouse T cell growth factor P40. The evidence is as follows: (a) recombinant P40 displayed all the biological activities ascribed to MEA: it supported the growth of MEA‐sensitive BMMC lines, it induced IL 6 secretion by these cells, and it enhanced survival of primary mast cell cultures; (b) highly purified MEA stimulated the growth of P40‐dependent cell lines; (c) a rabbit monospecific antiserum directed against P40 specifically inhibited the action of MEA on BMMC; (d) specific binding sites for P40 were detected on BMMC and (e) MEA competed with P40 for binding to P40‐dependent T cells, indicating that the two molecules interact with the same receptor. These observations further extend the range of biological activities ascribed to P40 and warrant its proposed designation as IL 9. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim