Biochemical characterization of the human basophil-promoting activity

Human T cells produce a factor that induces growth of metachromatically staining cells in human bone marrow cultures. These cultured cells contain metachromatically staining granules and release histamine upon triggering with IgE and anti-IgE antibody. Based on morphological criteria, these cultured cells were termed basophil-like cells. We have generated a human T hybridoma which produces this basophil-like cell-promoting activity (BaPA). BaPA has a molecular weight of approximately 20 kilodaltons and isoelectric points between pH 5.8 and 7.5, with a major peak at pH 7. BaPA is of protein nature and can be clearly separated from interleukin-1 (IL-1), IL-2, interferons, GM-CSF and M-CSF. BaPA is also clearly different from a human IL-3-like activity which by itself can induce growth of metachromatically staining cells containing lower histamine levels than the cells cultured in the presence of BaPA. The growth of human basophil/mast cell-like cells can furthermore be enhanced if human bone marrow cells are cultured in the presence of fibroblast feeder cells.