Biological properties of partially purified granulocyte extract (chalone) assayed in soft agar culture

The inhibitory effects of partly purified low molecular weight granulocyte extracts (GE) from human peripheral blood were investigated on mouse myelopoietic cells in agar cultures. By repeated freezing and thawing the inhibitory effect of the extract was lost, and instead a stimulatory effect was seen. The stimulation was seen mainly as an increase of colonies and clusters from the sixth day of culture. The degree of inhibition depended on the length of the preincubation time. After half an hour a stable and lasting inhibition was found. The biological effects of the extracts were temperature dependent. Inhibition or stimulation was seen when the target cells were exposed to GE at 37 degrees C and not at 4 degrees C. Colony formation in agar showed circannual variation with maxima in spring and autumn and minima in summer and winter. The data indicated that the inhibitory effect of GE did not show circannual variations.