Increased eosinophil colony formation in agar by haemopoietic cells from patients with the hypereosinophilic syndrome.

Colony formation by granulocyte/macrophage and eosinophilic progenitor cells in the blood and/or bone marrow of four patients with "hypereosinophilic syndrome' (HES) was studied in agar culture. Colony-stimulating activity (CSA) was derived from leucocyte feeder layers (LFL) or from medium conditioned by phytohaemagglutinin-stimulated lymphocytes (LCM). The total numbers of colonies in the patients' blood and marrow were normal. When patients' marrow cells were cultured over LFL, the proportion of colonies that were eosinophilic was greater than normal (mean 21% vs 6%, P less 0.001) and this difference was accentuated when CSA was derived from LCM (mean 53% vs 15%, P less than 0.001). LCM derived from normal subjects and LCM prepared from HES patients had similar effects. In the blood the total number of colonies and the proportion of eosinophilic colonies were similar in patients and controls. The overall pattern of colony formation HES differed distinctly from that observed in a patient with eosinophilic leukaemia reported previously. We conclude that the proportion of eosinophil-committed progenitor cells in the marrow of patients with HES is increased, but we have failed to demonstrate a role for the patient's own lymphocytes in augmenting eosinophil production.