Mast cells induced in vitro by interleukin 3 from native murine thymus cells

To shed further light on the induction and characterization of thymus-derived mast cells, we cultured a variety of cell populations from murine thymus tissues (Balb/c) in the presence or absence of interleukin 3 (IL-3). The whole cell population and the non-adherent T cell-depleted population developed mast cells. The morphological studies revealed granulated cells; the granules were stained with toluidine blue, alcian blue (pH 3.0), and metachromatic dyes. Electron microscopy revealed altered mast cell granules. These cells contained relatively low amounts of histamine (approximately 1700 ng/10(6) cells), were IL-3 (but not IL-2)-dependent, and did not possess T-cell, B-cell, or macrophage markers. No phagocytosis was observed. The cells also had 20 alpha-hydroxysteroid dehydrogenase, and both IL-3 and IgE (145,600/cell) high affinity receptors. The frequency analysis showed 17 precursor cells per 10(6) thymic cells. The results indicate that the thymus indeed contains progenitors of mast cells responsive to IL-3, and that the mast cells are derived from non-T, non-phagocytic, and non-adherent cells of the thymus. Their T-lymphocyte product (IL-3) dependency, ultrastructural appearance, granular stainability, and low content of histamine may support the view that the mast cells originating from the thymus probably belong to a mucosal mast cell lineage.