Selective growth of human mast cells induced by Steel factor, IL-6, and prostaglandin E2 from cord blood mononuclear cells.

To establish the method for generating a large number of mature human mast cells, we cultured cord blood mononuclear cells (CBMC) in several conditions in the presence of Steel factor (SF). Among several cytokines tested, IL-6 enhanced SF-dependent mast cell growth from purified CD34+ cells for more than 8 wk in culture. When CBMC were cultured instead of CD34+ cells, IL-6 enhanced the mast cell development in the presence but not in the absence of PGE2. PGE2 enhanced the SF- and IL-6-dependent development of mast cells from CBMC probably by blocking granulocyte-macrophage CSF (GM-CSF) secretion from accessory cells, because 1) PGE2, or anti-GM-CSF enhanced the mast cell development induced by SF and IL-6 from CBMC, but not from CD34+ cells; 2) GM-CSF inhibited the enhancing effect of IL-6 on the mast cell development from CD34+ cells; and 3) PGE2 inhibited GM-CSF secretion from CBMC. The mast cells cultured in the presence of SF, IL-6, and PGE2 for >10 wk were 99% pure, and seemed to be functionally mature, because 1) they contained 5.62 micrograms of histamine and 3.46 micrograms of tryptase per 10(6) cells; and 2) when sensitized with human IgE and then challenged with anti-human IgE, the cells released a variety of mediators such as histamine, and an increase in intracellular Ca2+ was found in advance of the activation of membrane movement by using a confocal laser-scanning microscope. Electron-microscopic analysis revealed that some of the cultured mast cells are morphologically mature since they filled with scroll granules and contained crystal granules.