Rat IL-3 stimulates the growth of rat mucosal mast cells in culture.

Rat mast cells with the properties of mucosal mast cells (MMC) proliferate in cultures of haemopoietic tissue in the presence of conditioned medium (CM) from antigen- or mitogen-activated T lymphocytes. The present study shows that recombinant rat interleukin-3 (rIL-3) both stimulated the development of MMC from bone marrow (BM) precursors and maintained the proliferation of rat MMC lines in an identical manner to that of CM. The content per cell of the MMC granule-specific proteinase RMCPII was similar in both IL-3- and CM-stimulated cultures. Passage of CM through DEAE-cellulose separated two active peaks that stimulated autologous MMC proliferation. The biochemical properties of peak 1 were similar to those of murine IL-3 and stimulated multi-potential stem cell development in soft agar cultures of BM cells from rats treated with 5-fluorouracil (which enriches for haemopoietic stem cells). RIL-3 was also active in this assay whereas peak 2 was not, demonstrating that peak 1 contained IL-3 activity. The presence of MMC in the majority of multi-potential colonies in the soft agar cultures confirmed the early stem cell origin of the MMC lineage. The cultured BM-derived mast cells in the rat are analogues of the MMC subset that is most readily observed proliferating in the gastrointestinal tract in response to helminth parasite infection. The demonstration that IL-3 is responsible for the development and proliferation of MMC should lead to a better understanding of the functional roles of these cells.