Abstract
We used functional expression cloning in mammalian cells to identify a cDNA clone encoding a hematopoietic growth factor that is mitogenic for the factor-dependent human megakaryoblastic leukemic cell line, MO7E. Analysis of the sequence of this cDNA revealed striking similarity to that of a recently reported novel murine growth factor for helper T- cell clones designated T-cell growth factor P40. The mRNA for the human P40 protein is expressed by several different human T-cell lines and by mitogen-stimulated peripheral blood lymphocytes. The recombinant protein displays substantial size heterogeneity typical of other glycoprotein cytokines. These properties plus the observation that this cytokine may well act within both the lymphoid and myeloid lineages warrant the designation of P40 as interleukin-9.
