Spontaneous release of a factor with interleukin-3-like activity by human lymphocytes and monocytes.

The production of a factor with interleukin-3-like activity (IL-3-LA) by cultured human peripheral-blood mononuclear cells has been studied. Culture supernatants spontaneously derived from lymphocytes or monocytes stimulated the proliferative activity of 3 IL-3-dependent cell lines. Purification of this factor by gel filtration-high-pressure liquid chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing demonstrated the presence of a glycoprotein with a molecular weight of 25-30 kilodaltons and an isoelectric point of 7.6. The biochemical characteristics of the IL-3-LA derived from human monocytes and lymphocytes were very similar. The biological activity of the semipurified factor was tested on mononuclear cells from fetal cord blood. It was found that after 21 days 40% of the cells in the culture were mature basophils which released 15-18 ng histamine/10(6) cells.