Screening for granulopoiesis inhibitors (chalones) by different assays.

The suitability of various granulocyte chalone sources was examined; for this purpose rat ascites fluid and the conditioned media of ascites and bone marrow cells were fractionated by ultrafiltration and Sephadex gel filtration. To evaluate different assay systems, the ability of the fractions to inhibit the growth of granulocytic and T-lymphocytic colonies in agar capillaries, as well as to inhibit the uptake of [3H]thymidine in bone-marrow cells, T- and B-lymphocytes, was tested and compared. Three granulocyte colony inhibiting fractions were obtained that contained apparent chalone activities, but showed different elution parameters with molecular weights well below 10 000. Comparison of the test systems revealed that the granulocyte colony assay may detect inhibitors different from those found by the [3H]thymidine bone-marrow assay; the validity of the latter test is seriously questioned, however. The need for precisely defined assays to screen for the apparently various inhibitors is emphasized by these studies.