Corticosteroids and granulopoiesis: effects upon in vitro colony formation

6 alpha Methylprednisolone (MP) and prednisone treatment of mice and man causes reduced in vitro colony formation in soft agar in the presence of added colony stimulating activity (CSA). MP or prednisone administration sharply reduces the amount of CSA released from white blood cell feeder layers and the CSA released into the serum of mice given endotoxin. The reduction in colony formation by the marrow of MP treated subjects is explained by the diminished endogenous CSA elaboration by CSA producing cells over the seven day assay period; the colony forming cells (CFC) are capable of responding to increased added CSA. There is no evidence for diminished in vivo granulopoiesis following MP treatment; hence in vitro colony formation is not a valid corollary of in vivo granulopoiesis in the presence of high dose corticosteroid treatment.