Stimulation of myeloid colony growth from peripheral blood by medium with an initially low osmolality

The clonal growth of myeloid colonies from peripheral blood was maximal when cultures were established with an initial osmolality of 220 mosmol/kg which increased during incubation as a result of partial drying. When osmolality was stabilized by secondary humidification, the optimum osmolality was 270 mosmol/kg, but growth was always two- to fivefold less than similar cultures established at low osmolality and incubated on an open shelf. Cultures established at 270 mosmol/kg or above were statistically similar whether or not drying was eliminated. Maximum colonies were apparent after 14 days incubation under both conditions; addition of conditioned medium did not alter the pattern of growth. The greater sensitivity of cultures established at 220 mosmol/kg is advantageous when assaying circulating progenitors in pathological conditions where a low number of granulocyte/macrophage colony-forming units is common.