Non-specific and specific effects of a granulocytic bio-inhibitor on different haematopoietic cell populations

The effect of a leucocyte conditioned medium derivative on the 5-125iodo-2'-deoxyuridine (125I-UdR) uptake by 6 haematopoietic cell populations with a simple in vitro assay system was tested. The low doses of the test substance--a putative granulocytic chalone--inhibited significantly the uptake of 125I-UdR only in predominantly granulocytic cell cultures. This inhibition was achieved using micrograms/ml concentrations, which have previously been shown to be inhibitory to normal and malignant granulocytic cells in vivo. The test preparations inhibited the uptake of 125I-UdR in all cell populations (nongranulocytic included) when doses exceeding 10 micrograms/ml were used. The prerequisite for an adequate demonstration of the specificity of a bio-inhibitor is discussed.