Eosinophil production in human bone‐marrow cultures induced by 80–85 kDa serum component(s) of patients with eosinophilia

Eosinophil production from normal human bonemarrow cells was induced by plasma or serum of patients with eosinophilia. After 10–12 d of liquid suspension culture, 14–42% of bone‐marrow cells were identified as maturing eosinophil granulocytes. Upon molecular sieve chromatography, the activity eluted in a single peak corresponding to a substance of 80–85 kDa molecular weight. The activity did not stimulate colony formation in semi‐solid agar media, but was detected in liquid suspension cultures only. Furthermore, addition of exogenous colony‐stimulating factor (CSF) had a differential effect depending on the culture system used. In semi‐solid media, predominance of eosinophil colonies was only observed when CSF was added at a low concentration. In liquid suspension cultures, however, 30–40% of cultured cells were eosinophils independent of the CSF concentration used. These findings extend recent studies in an animal model and support the hypothesis that a differentiation factor is involved in the regulation of eosinophil production in man.