Fibroblast precursors in normal and irradiated mouse hematopoietic organs.

Using the in vitro colony assay, clonogenic fibroblast precursor cells (CFU-F) were detected in the bone marrow, spleen and thymus from adult mice. The survival curve for CFU-F of mouse bone marrow irradiated in vitro has a D0 of 220 r. Regeneration of bone marrow CFU-F after whole-body irradiation with 150 r is characterized by a marked secondary loss and post-irradiation lag and dip, lasting 6 days, followed by return to normal values by about the 25th day. This pattern of post-radiation recovery of CFU-F is similar to that of the CFU-s. In addition, during the first 6 hours following irradiation the number of CFU-F increased approximately twofold.