Characterization of mast cell precursors by physical means: dissociation from T cells and T cell precursors.

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Abstract
Murine bone marrow precursors (MCP) differentiate into mast cells and proliferate in response to mast cell growth factor (MCGF). An assay system based on the incorporation of [3']thymidine by proliferating mast cells in response to substantially purified MCGF was used to titrate MCP. Murine bone marrow was separated into fractions by Percoll density gradient centrifugation or velocity sedimentation at unit gravity. Individual fractions were analyzed to determine the relative concentrations of MCP. To determine if mast cells were derived from precursors different from those for T lymphocytes and granulocytes and macrophages, separated cells were also analyzed for responsiveness to interleukin 2 (IL 2) in standard [3H] thymidine incorporation assays and to granulocyte-macrophage colony stimulating factors (CSF) in agar cloning (CFU-GM) assays. Cultured marrow cells from Dexter type long-term marrow cultures (LMC) were included as a source of marrow cells devoid of mature T cells, so as to dissociate MCP from pre-T cells. MCP were readily dissociable from T cells and/or pre-T cells present in fresh, as well as cultured, marrow cells by either density or velocity of sedimentation separation techniques. MCP were, however, not readily separable from CFU-GM. Nevertheless, MCP appeared not to share a common precursor with pure macrophage type colony-forming cells (CFU-M phi). The implications of the findings on the lineage origin of mast cells were discussed.