Cultured human cord blood cells spontaneously produce a factor with basophil-promoting activity

Cord blood is a source for pluripotential stem cells capable of differentiating into various hemopoietic cell lines in the presence of suitable specific growth factors. Without additional growth factors, cultured cord blood cells give rise to large numbers of basophils. We have recently defined a human basophil growth promoting factor, designated as interleukin-3-like activity (IL-3-LA), produced spontaneously by human monocytes and lymphocytes. In order to explain the phenomenon of spontaneous basophil development in cord blood cultures, we studied the relationship between basophil production and IL-3-LA release in these cultures. IL-3-LA produced by cord blood mononuclear cells increased from day 3 to day 14 and then decreased gradually by day 35. Basophil development was observed from day 14 on (33% +/- 6.4) and peaked on day 21 (51% +/- 7.4). Histamine release followed the same pattern i.e., 10 +/- 3.4 ng/ml on day 14, and 23 +/- 6.5 ng/ml on day 21. It is suggested that IL-3-LA spontaneously released by cord blood mononuclear cells induces basophil development in these cultures.