Stimulator of proliferation of spleen colony-forming cells in acute sterile inflammation

The presence and activity of a spleen colony‐forming cell (CFU‐S) proliferation stimulator was investigated in rat bone marrow after induction of sterile inflammation. Wistar rats were treated intraperitoneally with two 15 ml injections of 3.5% polyvinylpyrrolidone (PVP) at 18 h intervals, and the presence of CFU‐S proliferation stimulator determined in bone marrow 6, 20 and 24 h after the first injection. The marrow of these mice was used to condition medium which was then fractionated using Amicon Diaflo ultrafiltration membranes. The 30–50 kDa fraction, taken from 20 h post‐PVP‐bone marrow extract, was found to induce cycling of d8‐CFU‐S in normal mouse bone marrow. This activity was not related to the presence of interleukins‐1, ‐2 or ‐6 like activities in the material tested. The results demonstrate the existence of CFU‐S proliferation stimulator in the bone marrow of rats with sterile inflammation (i.e. in an in vivo tissue response to non‐specific cell stimulation), similar to that originally described as a macrophage product in mouse bone marrow after treatment with a variety of cytotoxic agents.