Osteoblast-like cell line maintains in vitro rat peritoneal mast cell viability and functional activity

We studied the ability of the rat osteosarcoma derived cell-line with osteoblastic properties ROS-17/2.8 (ROS) to maintain in vitro rat peritoneal mast cells (MC) in a functional state. Highly purified (> 95%) MC were seeded on confluent ROS cells. The MC adhered tightly to the monolayers within a few hours and remained viable for at least 2 weeks, but did not proliferate. The MC retained their typical appearance, exhibiting highly granulated resting morphology when stained with alcian blue followed by safranin or with acidic toluidine blue. Futhermore, after 2 weeks, the MC were fully responsive to activation with compound 48/80 (3 μg/ml), releasing 75% of their histamine content, as compared to 3% in the absence of the secretagogue. Utilizing metabolically inactive ROS cells and prevention of contact between ROS and MC, we found that both release of factor(s) and cell-cell contact were required by ROS to exhibit their MC supporting activity. Various other cells and cell lines were unable to support MC viability. On the other hand, as demonstrated before, 3T3 fibroblasts were capable of promoting MC viability. Thus, MC viability and functional activity are specifically maintained by fibroblastic and osteoblastic cells. The abundance of MC in bone, and their participation in bone remodelling raise the possibility of physiological and pathological significance to interactions between MC and osteoblasts.