Purification of MEA, a mast cell growth-enhancing activity, to apparent homogeneity and its partial amino acid sequencing

A novel growth factor for bone marrow derived murine mucosal type mast cells has been isolated from the conditioned medium of the Mlsa-reactive mouse Th cell line MLS-4.2. In proliferation assays this growth factor synergizes, like IL-4, with IL-3 on established mast cell lines and was therefore termed MEA: mast cell growth enhancing activity. MEA was characterized as a glycoprotein with a Mr range between 37,000 and 43,000. Apparent homogeneity was obtained by using a four-step purification scheme including cation exchange chromatography, Procion red affinity chromatography, IEF, and gel filtration. Inasmuch as MEA was N-terminally blocked during automated Edman-degradation, peptide fragments after digestion with trypsin were used for partial amino acid sequence determination. All evaluable MEA peptide fragments showed complete sequence homology to a recently purified and cloned novel T cell growth factor (P40/TCGF III), the mouse homologue of human IL-9.